91-EM-045-HN04_REVA © ConsuLab Educatech Inc, 2026. All rights reserved. Answer Keys for EM-045-HN04_053401 Student-built 1-cylinder engine Teacher Only 91-EM-045-HN04 Table of contents 400-6330 Zéphirin-Paquet St. Québec QC G2C 0M3 Canada consulab.com info@consulab.com Toll-free: +1 (800) 567-0791 USA: +1 (810) 222-4525 Canada: +1 (418) 688-9067 Fax: +1 (418) 843-3444 2 Table of Contents Student Assignments Instructor Notes and Answer Keys About This Manual 5 SA-1 - Level I — Engine Familiarization and Component Identification 6 Instructor Notes 6 Answers 7 SA-2 - Level I — Engine Teardown and Component Relationships 10 Instructor Notes 10 Answers 11 SA-3 - Level II — Understanding Engine Timing 13 Instructor Notes 13 Answers 14 SA-4 - Level II — Ignition Coil Positioning and Adjustment 18 Instructor Notes 18 Answers 19 SA-5 - Level II — Valve Clearance Adjustment 23 Instructor Notes 23 Answers 24 SA-6 - Level I — Spark Plug Adjustment 28 Instructor Notes 28 Answers 29 SA-7 - Level III — Piston Ring End Gap Adjustment 33 Instructor Notes 33 Answers 34 91-EM-045-HN04 Table of contents 400-6330 Zéphirin-Paquet St. Québec QC G2C 0M3 Canada consulab.com info@consulab.com Toll-free: +1 (800) 567-0791 USA: +1 (810) 222-4525 Canada: +1 (418) 688-9067 Fax: +1 (418) 843-3444 3 © ConsuLab Educatech Inc, 2026. All rights reserved. No part of this work may be reproduced or transmitted in any form by any means, electronic, mechanical, including photocopying and recording, or by any information storage or retrieval system, without written permission from the publisher. Printed in Canada. The content of this manual is applicable to models 053401 and above. SA-8 Level I Engine Reassembly 38 Instructor Notes 38 Answers 39 Engine Fundamentals Assessment 42 Glossary 45 Manufacturer Specifications Torque Specifications 50 Honda GX35 Specifications 51 consulab.com info@consulab.com 4 91-EM-045-HN04 Student Assignments — Instructor Notes and Answer Keys Student Assignments Instructor Notes and Answer Keys consulab.com info@consulab.com 5 91-EM-045-HN04 About This Manual About This Manual Welcome to the ConsuLab Student Manual! This manual is designed to support your learning as you use this training aid. The information below will help you under- stand how the manual is organized and how to use it effectively. Glossary A Glossary is provided at the back of this manual. It contains definitions for key technical terms and core vocabulary used throughout the manual. • Words shown in bold text are core vocabulary terms • All bold terms are defined in the Glossary Text Formatting Different text styles are used to highlight important information: • Bold text Indicates important terms or concepts. These words are defined in the Glossary. • Italic text Indicates helpful hints, notes, or additional explanations intended to support understanding. • Red text Indicates warnings or cautions. Pay close attention to this information to avoid potential errors, damage, or safety risks. Diagrams and Schematics Detailed diagrams, schematics, and visual references are located in the back of this manual. These resources support the material presented in each section and may be referenced throughout the text. consulab.com info@consulab.com 6 91-EM-045-HN04 SA-1 - Level I — Engine Familiarization and Component Identification SA-1 - Level I — Engine Familiarization and Component Identi- fication Instructor Notes Teaching Suggestions • Use one fully assembled and running engine to walk students through component locations and briefly relate each part to its role in engine operation as the engine is operating. • Before the sequencing activity, show a short video or animation of a four-stroke overhead cam engine to help stu- dents visualize piston, valve, and crankshaft motion. • After Parts 1 and 2, students may benefit from sorting glossary terms into engine systems (intake, ignition, exhaust, mechanical) to strengthen understanding of how components work together. Practical Applications • Relate engine components and operation to routine vehicle experiences, such as starting a car, hearing exhaust noise, or noticing rough idle, to help students connect theory to everyday observation • Reinforce glossary and system concepts by discussing basic maintenance tasks students may already be familiar with, such as checking an air filter, adding fuel, or noticing warning signs of poor engine performance. • Connect the overhead cam design to modern vehicles and small equipment students may use or see, such as com- pact cars, motorcycles, lawn mowers, or generators. consulab.com info@consulab.com 7 91-EM-045-HN04 SA-1 - Level I — Engine Familiarization and Component Identification Answers Objective: Identify engine components and classify each by function and system. Material Required: EM-045-HN04 Part 1 – Component Identification Examine the assembled engine and locate each component listed in the table below. For each component, identify its physical location on the engine and describe its primary function. Reference the glossary, as needed. Component Location on Engine Primary Function Air Filter On intake side of engine Cleans incoming air before it enters the engine Carburetor Side of engine, under air filter Mixes air and fuel so the engine can run Spark Plug Threaded into top of cylinder head Creates a spark to ignite the fuel mixture Rocker Cover Top of engine above valves Protects rocker arms and valve parts Muffler Exhaust side of engine Reduces engine noise during exhaust Recoil Starter Front of engine Spins the engine to start it Fuel Tank Mounted beside engine Stores fuel for engine operation Ignition Coil Near flywheel on engine side Creates high voltage for the spark plug Flywheel Side of engine behind cover Stores rotation and helps smooth engine speed PCV Vent Tube Hose from crankcase to intake Releases pressure from inside the engine Fuel Supply Line Hose from fuel tank to carburetor Carries fuel to the carburetor consulab.com info@consulab.com 8 91-EM-045-HN04 SA-1 - Level I — Engine Familiarization and Component Identification Part 2 – Engine Operation The engine used in this trainer is a single-cylinder, four-stroke, overhead cam (OHC) engine. In an overhead cam engine, the camshaft is located in the cylinder head above the valves. This design allows the camshaft to open and close the intake and exhaust valves more directly and accurately. Overhead cam engines are commonly used in modern vehicles because they improve engine efficiency, performance, and precision compared to older cam-in-block designs. Examples of vehicles that commonly use overhead cam engines include a Honda Civic, Toyota Corolla, Ford Focus, and many modern motorcycles and lawn equipment. An internal combustion engine operates through a series of events that occur repeatedly while the engine is running. The steps below describe how an overhead cam, four-stroke engine begins operating starting from engine start-up, but the steps are listed out of order. Read all steps carefully and number them 1 through 10 to show the correct sequence of events from pulling the recoil starter through exhaust. 6 The piston moves upward and compresses the air-fuel mixture inside the cylinder. 1 Pulling the recoil starter turns the crankshaft and flywheel. 3 The timing belt keeps the camshaft and crankshaft synchronized. 10 The exhaust valve opens and the piston pushes burned exhaust gases out of the cylinder. 4 The camshaft rotates inside the cylinder head to control valve movement. 7 The spark plug fires, igniting the compressed air-fuel mixture. 8 Combustion forces the piston downward during the power stroke. 5 The intake valve opens as the piston moves downward, drawing air and fuel into the cylinder. 9 The crankshaft rotates as piston force is transferred through the connecting rod. 2 Engine rotation continues as the flywheel stores and smooths rotational energy. consulab.com info@consulab.com 9 91-EM-045-HN04 SA-1 - Level I — Engine Familiarization and Component Identification Part 3 – Engine Systems Thinking 1. Which components are directly involved in allowing air and fuel to enter the engine? Select all that apply. Air filter Carburetor Intake valve ☐ Spark plug ☐ Muffler 2. Why is it important for the timing belt to keep the camshaft and crankshaft synchronized in an overhead cam en- gine? What could happen if they are not synchronized? It is important because the camshaft controls the valves and the crankshaft controls the piston. If they are not syn- chronized, the valves could open at the wrong time, causing poor engine operation or engine damage. 3. The engine is running at idle and suddenly begins to run rough. Which system would be checked first based on how the engine operates: air intake, ignition, or exhaust? Justify your choice in a complete sentence. The air intake system should be checked first because the engine needs clean air and the correct air-fuel mixture to run smoothly. If airflow is restricted, combustion will not happen properly. consulab.com info@consulab.com 10 91-EM-045-HN04 SA-2 - Level I — Engine Teardown and Component Relationships SA-2 - Level I — Engine Teardown and Component Relation- ships Instructor Notes Teaching Suggestions • Before students touch the engine, briefly review how to use the specialized tools used in this assignment, particu- larly the flywheel puller and puller adapter. Emphasize why certain tools exist (for example, adapters that protect crankshaft threads) to reinforce that proper tools prevent damage, not just make work easier. • Demonstrate correct flywheel handling and explicitly warn against prying on fins. Explain how the flywheel’s tapered fit requires even, controlled pressure and why the puller must be tightened evenly. Reinforce that cracked fins or damaged tapers are common real-world mistakes caused by rushing or improper leverage. • Before removing the timing belt, stop students and visually identify timing marks on the flywheel and engine casing, as well as belt orientation lettering. Reinforce that these marks exist to make reassembly possible and that missing them during teardown creates major problems later. • When students reach the crankshaft, piston, and internal rotating components, explain that some assemblies are not intended to be dismantled further. Use this moment to teach decision-making: knowing when to stop disassembling is a key professional skill that prevents unnecessary damage and wasted time. • The short-handled wrench provided with this product doesn’t easily generate a lot of hand torque, if you have larger tools of the same size consider using them, particularly for tight components, like the flywheel and sparkplug. Practical Applications • Explain that modern vehicle engines commonly use aluminum housings where incorrect bolt placement or length can crack components or distort sealing surfaces. The organization skills practiced here directly apply to oil pans, timing covers, cylinder heads, and valve covers on full-size engines. • Point out that most passenger vehicles today use overhead cam or dual overhead cam designs. The camshaft-over- valve layout the students observed is the same principle used in automotive engines, even though those systems may include multiple camshafts and more complex timing drives. • Explain that multi-cylinder engines repeat the same mechanical system students disassembled here. What they ob- served, like piston movement, valve timing, and crankshaft rotation, occurs multiple times in four-, six-, or eight-cylinder engines. consulab.com info@consulab.com 11 91-EM-045-HN04 SA-2 - Level I — Engine Teardown and Component Relationships Answers Objective: Disassemble the engine and analyze how components interact to perform mechanical work. Material Required: EM-045-HN04, tool bag Part 1 – Pre-Disassembly Confirmation Before beginning any disassembly, confirm the following: ☐ Fuel has been drained from the engine and fuel tank has been removed ☐ Engine oil has been drained using the drain port ☐ Work area is clean and organized for disassembly Instructor Initials: Part 2 – Engine Disassembly Use the Disassembly Instructions found in the EM-045 Assembly Manual to disassemble the engine.. As you disassemble, complete the sections below. For each disassembly section, write 2–3 key takeaways to remember when disassembling this portion of an engine again. Takeaways may include: NOTE: Answers will vary, samples are provided below. • fastener placement or length • order of removal • tools required • cautions or “do not do this” notes • questions you still have • tips to remember next time A. Intake and Exhaust Components 1. The black plastic air filter housing is opened using a pinch-type tab; no tools or prying needed 2. Phillips-head screws around choke and throttle area do not need to be removed 3. Three 4mm hex bolts of same length, One 4mm hex bolt that is slightly longer goes in bottom middle under air filter consulab.com info@consulab.com 12 91-EM-045-HN04 SA-2 - Level I — Engine Teardown and Component Relationships For each disassembly section, write 2–3 key takeaways to remember when disassembling this portion of an engine again. B. Removing the Flywheel 1. The flywheel fins are fragile and easily bent. Do not pry on them; could damage and/or impact engine cooling 2. The flywheel must be held securely to loosen the retaining nut. Using the puller and/or a secondary tool for lever- age makes removal easier 3. The puller must be mounted square and tightened evenly using all mounting bolts. Leave a gap between tool and flywheel for the puller to have room to pull C. Internal Engine Components 1. When the timing belt was removed, the bottom of the HONDA lettering on the belt is closest to the piston 2. The intake valve has a larger head (15.5mm), while the exhaust valve is smaller (14.0mm), use calipers if can’t tell the difference. 3. The crankshaft assembly should not be disassembled further; it is replaced as a unit. Part 3 – Engine Teardown Observations 1. What does it mean that this engine is a single-cylinder engine, and how did you observe this during disassembly? This engine is a single-cylinder engine because it has only one cylinder and one piston that produces power. During disassembly, I observed one piston, one combustion chamber, and one set of intake and exhaust valves, which con- firms it is a single-cylinder engine. 2. Choose two components that interact directly during engine operation. NOTE: Answers will vary. (example: piston and crankshaft, camshaft and valves, timing belt and cam gear). Component 1: Camshaft Component 2: Valves Describe how these two components work together to produce or control mechanical motion. The camshaft and valves work together to control airflow in the engine. As the camshaft rotates, it pushes on the rocker arms, which open and close the intake and exhaust valves at the correct time. consulab.com info@consulab.com 13 91-EM-045-HN04 SA-3 - Level II — Understanding Engine Timing SA-3 - Level II — Understanding Engine Timing Instructor Notes Teaching Suggestions • Begin with a quick demonstration of cam and crank gear rotation to visually show the 2:1 relationship. Have stu- dents count rotations to reinforce the concept. • Emphasize the difference between Top Dead Center (TDC) on compression vs. exhaust, students often confuse these. Use slow rotation and point out valve position to clarify. • During belt inspection, prompt students to explain why each condition (cracks, wear, damage) matters rather than just checking boxes. • Reinforce correct belt installation by having students verbally explain their steps before performing the task. • Circulate during the reinstall task and check for common errors: - Misaligned timing marks - Belt skipping a tooth - Incorrect belt orientation (lettering direction) Practical Applications • Relate improper timing to common customer concerns: - No-start condition - Rough running or misfire - Loss of power • Discuss how small errors (off by one tooth) can lead to major performance issues or engine damage, especially in interference engines. • Reinforce how technicians use timing marks and service information to ensure accuracy, not guesswork. • Link belt inspection to real shop decisions, students should understand when a belt is safe to reuse vs. requiring replacement. Bonus show worn timing belts as non-examples if you have them. • Highlight the importance of verifying work by manually rotating the engine after installation to confirm proper timing before start-up. consulab.com info@consulab.com 14 91-EM-045-HN04 SA-3 - Level II — Understanding Engine Timing Answers Objective: Perform cam-to-crank timing alignment and justify its importance to engine function. Material Required: EM-045-HN04, tool bag Part 1 – Engine Timing Explained Cam-to-crank timing refers to the precise synchronization between the crankshaft and camshaft(s) in an internal com- bustion engine, ensuring that the pistons and valves operate in exact relation to one another throughout the four-stroke cycle. The crankshaft converts the up-and-down movement of the pistons into rotational force, while the camshaft controls the opening and closing of the intake and exhaust valves. This timing relationship, typically maintained by a timing belt, chain, or gear set, ensures valves open at the correct moment for air-fuel intake, compression, combustion, and exhaust gas removal. Proper cam-crank timing is critical for engine performance, fuel efficiency, emissions control, smooth operation, and preventing severe engine damage. If timing is incorrect by even a few teeth, the engine may run poorly, misfire, lose power, fail to start, or in interference engines, allow pistons to contact open valves, causing cata- strophic mechanical failure. The EM-045 engine trainer includes two main components for cam–crank timing: the cam gear and the crank gear. These gears synchronize the rotation of the crankshaft and camshaft(s), ensuring the valves and pistons operate in the correct sequence. The crank gear, mounted to the crankshaft, is the driving gear. It transfers rotation from the crankshaft (moved by the pistons) to the camshaft through a timing belt, chain, or gear set. In a four-stroke engine, it maintains a 2:1 ratio, meaning the crankshaft turns twice for every one turn of the camshaft. The cam gear, mounted to the camshaft, is the driven gear. It controls when the intake and exhaust valves open and close so the engine can take in air/fuel, produce power, and expel exhaust. consulab.com info@consulab.com 15 91-EM-045-HN04 SA-3 - Level II — Understanding Engine Timing 1. Count the number of teeth that are on each of the gears. Cam – Larger gear : 30 Crank – Smaller gear : 15 2. Complete the summary below using the word bank. Word Bank: crankshaft, camshaft, valves, pistons, timing belt, 2:1, power, timing Cam-to-crank timing keeps the crankshaft and camshaft working together. The crankshaft moves up and down, while the camshaft controls when the valves open and close. The timing belt or gears connect these components and keep them in sync. In a four-stroke engine, the crankshaft turns in a 2:1 ratio compared to the camshaft. This timing allows the engine to run properly and produce power. Part 2 – Piston Position and Timing When timing an engine it’s important to understand the differences of top dead center and bottom dead center. Top dead center (TDC) is the exact position where the piston reaches the highest point of travel inside the cylinder, closest to the cylinder head. This position occurs twice during a four-stroke engine cycle, once at the end of the compression stroke (when the air-fuel mixture is ready for ignition) and again at the end of the exhaust stroke (when exhaust gases have been expelled). TDC is a critical reference point used for engine timing, ignition timing, camshaft alignment, valve timing, and many service procedures, like timing belt replacement. Bottom dead center (BDC) is the exact position where the piston reaches the lowest point of travel inside the cylinder, farthest from the cylinder head. This also occurs twice during the four-stroke cycle, once at the end of the intake stroke and again at the end of the power stroke. BDC serves as an important reference for understanding piston movement, crankshaft rotation, engine displacement, and valve timing events. consulab.com info@consulab.com 16 91-EM-045-HN04 SA-3 - Level II — Understanding Engine Timing 3. Locate the timing arrow (sometimes called an alignment mark) on the cam gear, then locate the timing arrow for the crankshaft on your engine. Completed? Yes/No 4. Inspect the timing belt. Place a ✓ if the belt passes inspection (no issues found): ☐ No cracks present ☐ No visible damage ☐ No signs of wear 5. Examine the timing belt to complete the service information below: A. Name of belt Manufacturer: Honda B. Manufacturer Part Number: 1440-Z3F-801 C. Number of teeth on belt: 76 6. Based on the image, describe how to properly reinstall the timing belt. Use the words “Honda” and “piston” in your explanation. When reinstalling the timing belt, it is important to make sure the cam gear and crank gear timing marks are properly aligned so the piston and valves stay in the correct position. The piston should be set to top dead center before installing the belt. Place the belt so the HONDA lettering on the belt is parallel to the piston. 8-2 GX35 • CAM PULLEY 3) Push the cam pulley shaft out from the valve spring side using a pin approximately 2 mm in diameter. 4) Remove the timing belt from the cam pulley, and remove the cam pulley. CAM PULLEY CAM PULLEY SHAFT CAM PULLEY SHAFT FAN COVER BOLT HOLE TIMING BELT CAM PULLEY ALIGNMENT MARKS HEAD COVER MATING SURFACE FLYWHEEL 8 REMOVAL: 1) Remove the spark plug, and head cover (P. 3-3, P. 8-1). 2) Set the piston at top dead center (TDC) of the compression stroke. When the piston is at TDC of the compression stroke, the f lyw heel al ignm ent m ark “ ” w i l l al ign w ith the fan cover bolt hole. Also, the cam pulley alignment marks will be positioned as shown. ALIGNMENT MARK TIMING BELT *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 8-2 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. 9-4 GX35 CYLINDER BLOCK • CRANKSHAFT INSPECTION: Check the o i l sl inger o f the crankshaf t for dam age and deform at ion. Replace the crankshaf t i f i t is dam aged or deformed. REASSEMBLY: 1) Install the timing belt on the timing gear crankshaft. When installing, pay attention to the direction of the letter on the timing belt as shown in the picture. • Replace worn or cracked tim ing belt. Do not bend or twist the timing belt. 2) Install the crankshaft in the cylinder block. 3) Apply a bead of l iqu id gasket to the cy l inder b lock; specifically to the mating surface of the crankcase cover. Install the crankcase cover on the cylinder block (P. 8-5). 4) Install the cam pulley and timing belt in the cam pulley and cylinder block (P. 8-2). • 10 x 20 x 5 mm OIL SEAL REASSEMBLY: 1) Set the oil seal on the crankshaft. 2) Install by aligning the oil seal projection with the groove in the cylinder block. 3) Install the lower crankcase (P. 8-5). OIL SLINGER OIL SLINGER CAM PULLEY TIMING BELT PISTON CRANKSHAFT 10 x 20 x 5 mm OIL SEAL CRANK SHAFT PROJECTION GROOVECYLINDER BLOCK *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 9-4 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. INSPECTION: P. 9-6 and 7 REASSEMBLY: • Install the second ring w ith the “ • ” or “ R” mark facing up. • Do not interchange the top ring and the second ring. • After assembly, check for smooth movement of the piston ring. • Stagger the piston ring end gaps 120° apart, Do not align with the piston pin. • Space the side rail end gaps at least 10 mm (0.4 in) apart. Coat the rings with oil after assembly. PISTON RING 9-1 GX35 9 9. CRANKSHAFT/PISTON/CYLINDER BLOCK/VALVES 1. CRANKSHAFT/PISTON 2. CYLINDER BLOCK/VALVES 3. INSPECTION 1. CRANKSHAFT/PISTON a. DISASSEMBLY/REASSEMBLY Remove the lower crankcase (P. 8-5). TOP RING 10 mm (0.4 in) SECOND RING “ • ” or “ R” MARK OIL RINGS (COMBINATION RINGS) 12 x 24 x 5 mm OIL SEAL PISTON INSPECTION: P. 9-6 and 7 REASSEMBLY: Install w ith the “ ” mark on the piston head facing the carburetor side. PISTON PIN DISASSEMBLY/ REASSEMBLY: P. 9-2 INSPECTION: P. 9-7 CRANKSHAFT INSPECTION: P. 9-4 REASSEMBLY: P. 9-4 10 x 20 x 5 mm OIL SEAL REASSEMBLY: P. 9-4 CARBURETOR SIDE TIMING BELT INSTALLATION: P. 9-4 Check that the belt is not worn or cracked. Do not bend or tw ist the belt. SECOND RING (BLACK CIRCUMFERENCE) OIL RINGS (COMBINATION RINGS) SIDE RAIL SPACER SIDE RAIL 10 mm (0.4 in) 120° 120° 120° “ ” MARK TOP RING (WHITE CIRCUMFERENCE) *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 9-1 Date of Issue: April 2006 © Honda Motor Co., Ltd. 4. ROCKER ARM/VALVE LIFTER © Honda Motor Co. consulab.com info@consulab.com 17 91-EM-045-HN04 SA-3 - Level II — Understanding Engine Timing 7. Based on how the timing belt is designed and installed, explain whether a timing belt can slip. In your answer, con- sider: A. How the belt connects to the gears B. What condition the belt and gears are in A timing belt normally does not slip because it has teeth that match with the gears on the crankshaft and camshaft. These teeth lock into place and keep both parts turning together. However, a timing belt can slip if it is damaged or worn. If the teeth on the belt or gears are missing or worn down, the belt may not stay in place and can lose timing. 8. Using the information from this assignment, properly reinstall the timing belt. Ensure all timing marks are aligned and the belt is installed correctly. Show your completed work to the instructor for verification. Instructor Initials: consulab.com info@consulab.com 18 91-EM-045-HN04 SA-4 - Level II — Ignition Coil Positioning and Adjustment SA-4 - Level II — Ignition Coil Positioning and Adjustment Instructor Notes Teaching Suggestions • Begin with a quick demo: manually rotate the flywheel and show how magnet position aligns with the ignition coil to introduce the concept of timing, then use a visual or diagram to reinforce the relationship between primary winding → magnetic field → collapse → secondary voltage → spark plug. Using one of the feeler gauges (not brass) see if the students can find the embedded magnets in the flywheel. • Have students predict what will happen before adjusting the air gap (too large vs too small) to build cause-and-effect reasoning. Ask guiding questions during the lab (e.g., “What happens to the magnetic field if the gap increases?”) to connect hands-on work to theory. • Emphasize vocabulary during instruction: primary winding, secondary winding, magnetic field, spark plug gap, timing, flywheel magnets. • Circulate during air gap adjustment to ensure proper feeler gauge technique and reinforce measuring at two points for consistency. • Emphasize the difference between magneto and 12-volt ignition systems. In a 12-volt automotive system, the crank- shaft position sensor air gap affects signal generation not spark energy directly. The sensor detects a reluctor or tone ring on the crankshaft and generates a signal as the teeth disturb its magnetic field. This signal is sent to the ECM/PCM, which then determines the correct timing to trigger the ignition coil and fuel injectors. Contrast this with the EM-045 magneto system, where coil positioning and air gap directly affect magnetic field strength and spark energy. Practical Applications • Reinforce that technicians must always verify air gap using feeler gauges and manufacturer specifications, not visual estimation. Highlight the importance of checking air gap at multiple points to ensure even spacing and consistent ignition timing. • Connect improper air gap to potential component damage, including flywheel-to-coil contact and long-term reli- ability issues. Discuss how correct ignition coil positioning directly affects spark timing, engine starting, and overall combustion efficiency. Optional Extension Use a digital multimeter to measure the primary and secondary winding resistance of the ignition coil and compare the values to manufacturer specifications; if available, use worn ignition coils for comparison to help students identify open circuits, shorted windings, and failing coils. consulab.com info@consulab.com 19 91-EM-045-HN04 SA-4 - Level II — Ignition Coil Positioning and Adjustment Answers Objective: Adjust ignition coil positioning and explain how crankshaft position determines spark timing. Material Required: EM-045-HN04, feeler gauges, manufacturer specifications Part 1 – The Purpose of the Ignition Coil In a gasoline engine, the ignition coil and spark plug work together to initiate combustion at precisely the right moment. When the ignition system signals the coil, current flows through the coil’s primary winding, creating a magnetic field. When this current is sud- denly interrupted, the magnetic field collapses rapidly across the secondary winding, inducing a high voltage surge. This voltage travels through the ignition lead or directly through a coil-on-plug design to the spark plug. The spark plug receives this electrical energy at its center electrode. When the voltage becomes high enough to overcome the resistance of the air-fuel mixture in the spark plug gap, an electrical arc jumps between the center and ground electrode. This spark generates intense heat, often exceeding 6,000°C, igniting the compressed air-fuel mixture inside the combustion chamber. The resulting combustion rapidly ex- pands gases that force the piston downward on the power stroke, producing usable engine power. Precise engine timing is critical, if the spark happens too early or too late, it can reduce engine performance, waste fuel, increase emissions, and damage engine parts. The ignition coil of the EM-045 operates using a magneto ignition system, meaning it generates spark energy inde- pendently without relying on a traditional 12-volt battery ignition system. As the engine’s flywheel rotates, embedded permanent magnets pass by the ignition coil (also called the ignition armature). This movement creates a changing magnetic field around the coil’s primary winding, generating electrical current. As the flywheel continues rotating and the magnet passes the coil at a precise crankshaft position, the ignition module rapidly interrupts the primary current flow. This sudden collapse of the magnetic field induces a much higher voltage in the coil’s secondary winding through electromagnetic induction. This high voltage, often several thousand volts, is then sent through the spark plug lead to the spark plug. At the spark plug, the voltage builds until it overcomes the resistance of the spark plug gap and the com- pressed air-fuel mixture inside the combustion chamber. A spark jumps across the electrodes, igniting the mixture near the end of the compression stroke. This combustion forces the piston downward, producing the power stroke. Because the GX35 is a four-stroke overhead cam engine, this ignition event must occur at the correct point in relation to piston position and valve timing. The ignition coil is mounted ad- jacent to the flywheel with a small air gap, making flywheel magnet position and coil condition critical for reliable spark production, smooth engine operation, and easy starting. Did You Know? The ignition coil acts as a high voltage transformer, boosting a vehicle’s 12 volts up to 20,000–60,000 volts or more to create the spark needed for ignition. 1-4 GX35 Black ICM IGNITION COIL SPARK PLUG Ignition switch on the equipment powered by the engine 4. WIRING DIAGRAM *GX35(E)_SEC.01-06 9/14/04 4:32 PM Page 6 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. consulab.com info@consulab.com 20 91-EM-045-HN04 SA-4 - Level II — Ignition Coil Positioning and Adjustment Part 2 – Understanding the Ignition Coil 1. Label the parts of the ignition pictured below. Word Bank: Ignition coil, high voltage ignition, primary wire, spark plug boot Ignition coil Spark plug boot High voltage Ignition wire Primary wire 2. What causes the ignition coil to produce high voltage in the secondary winding? A. A steady magnetic field in the coil B. The rapid collapse of the magnetic field in the primary winding C. Continuous current flow through the secondary winding D. Heat generated at the spark plug 3. Place the ignition events in the correct order: 2 Magnetic field collapses 4 Spark jumps across the spark plug gap 1 Current flows through the primary winding 3 High voltage is induced in the secondary winding 4. What happens when the spark jumps across the spark plug gap? When the spark jumps across the spark plug gap during the compression stroke, it creates intense heat that ignites the air-fuel mixture, starting combustion in the engine. consulab.com info@consulab.com 21 91-EM-045-HN04 SA-4 - Level II — Ignition Coil Positioning and Adjustment Part 3 - Adjusting Ignition Coil Air Gap © Honda Motor Co. 7-5 GX35 Adjustment is required only when the ignition coil or the fly- wheel has been removed. 1) Loosen the ignition coil bolts. Insert a feeler gauge between the ignition coil and the mag- netic part of the flywheel. 2) Push the ignit ion coi l f i rm ly tow ard the f lyw heel and tighten the bolts. • Adjust the clearance at the magnetic part of the flywheel. • Adjust both gaps at the right and left sides of the ignition coil simultaneously so they are equal. c. ADJUSTMENT • IGNITION COIL AIR GAP Specified clearance 0.2 – 0.4 mm (0.008 – 0.016 in) FEELER GAUGE 0.2 – 0.4 mm (0.008 – 0.016 in) MAGNETIC PARTS 0.2 – 0.4 mm (0.008 – 0.016 in) *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 7-5 Date of Issue: April 2006 © Honda Motor Co., Ltd. The air gap between the ignition coil and the flywheel magnets is critical as it directly affects the strength of the magnetic field used to generate spark energy. In a magneto ignition system, such as on a small gasoline engine, the flywheel magnets pass close to the ignition coil to create a changing magnetic field. The correct air gap ensures the coil receives the strongest possible magnetic field without physical contact, allowing the ignition system to generate reliable high voltage at the proper time. Proper adjustment is especially important for small engines where spark energy is entirely dependent on magnetic induction rather than battery power. Even a small change in air gap can significantly affect engine starting, combus- tion efficiency, and overall performance. If the air gap is too large, the magnetic field becomes weaker, reducing the amount of electrical energy produced. This can result in a weak spark, hard starting, engine misfires, poor performance, or even a complete no-start condition. If the air gap is too small, the flywheel may physically contact the ignition coil as the engine rotates, causing damage to the coil, magnets, or flywheel. A gap that is too tight can also create inconsistent spark timing due to mechanical interfer- ence. 5. Refer to the manufacturer specifications, what are the specifications for the air gap on the EM-045 engine? Specification: 0.2 – 0.4 mm (0.008 – 0.016 in) Use a non-magnetic feeler gauge to measure the air gap between the ignition coil and the flywheel. Position the gauge between the coil and flywheel at two different points to check that the gap is even. If needed, loosen the coil mounting bolts and adjust the coil until the correct air gap is set, then re-tighten the bolts to specifica- tion and recheck the gap. 6. A small engine is hard to start and has a weak spark. Tech A says the ignition coil air gap may be too large, reducing the strength of the magnetic field. Tech B says the ignition coil air gap may be too large, allowing more voltage to be produced. A. Technician A B. Technician B C. Both Technician A and B D. Neither Technician A nor B 7. A customer reports their engine makes scraping noise and is difficult to start. You measure the ignition coil air gap and find it is smaller than the manufacturer specification. Explain how this air gap condition is causing the customer concern. A small air gap can cause the flywheel to contact the ignition coil, leading to damage and inconsistent spark timing, which results in hard starting and poor engine operation. © Honda Motor Co. 7-5 GX35 Adjustment is required only when the ignition coil or the fly- wheel has been removed. 1) Loosen the ignition coil bolts. Insert a feeler gauge between the ignition coil and the mag- netic part of the flywheel. 2) Push the ignit ion coi l f i rm ly tow ard the f lyw heel and tighten the bolts. • Adjust the clearance at the magnetic part of the flywheel. • Adjust both gaps at the right and left sides of the ignition coil simultaneously so they are equal. c. ADJUSTMENT • IGNITION COIL AIR GAP Specified clearance 0.2 – 0.4 mm (0.008 – 0.016 in) FEELER GAUGE 0.2 – 0.4 mm (0.008 – 0.016 in) MAGNETIC PARTS 0.2 – 0.4 mm (0.008 – 0.016 in) *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 7-5 Date of Issue: April 2006 © Honda Motor Co., Ltd. consulab.com info@consulab.com 22 91-EM-045-HN04 SA-4 - Level II — Ignition Coil Positioning and Adjustment Optional Extension – Ignition Coil Electrical Testing Materials: Digital multimeter or ohmmeter 1-4 GX35 Black ICM IGNITION COIL SPARK PLUG Ignition switch on the equipment powered by the engine 4. WIRING DIAGRAM *GX35(E)_SEC.01-06 9/14/04 4:32 PM Page 6 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. Secondary winding Primary winding Testing the primary and secondary winding resistance of an ignition coil is important because it helps determine the electrical health and internal condition of the coil. Compar- ing measured resistance values to manufacturer specifica- tions allows technicians to quickly identify open circuits, shorted windings, or failing coils before complete failure occurs. Testing the primary winding resistance checks the condition of the low-voltage winding that receives power from the ig- nition system or engine control module. If resistance is too high, current flow is restricted, resulting in a weak magnetic field and poor spark energy. If resistance is too low, it may indicate an internal short, causing excessive current draw, overheating, or damage to the ignition module or ECM. Testing the secondary resistance evaluates the high-voltage wind- ing that delivers spark energy to the spark plug. Excessive resistance may indicate broken windings, corrosion, or internal deterioration, leading to weak spark, misfires, poor performance, or hard starting. Very low resistance can suggest an internal short within the coil. Use the manufacturer specifications below to test the primary and secondary windings of the EM-045. Testing the Primary Winding Testing the Secondary Winding Primary Specification: 0.75 – 0.92 Ω Secondary Specification: 6.1 – 9.3 kΩ 7-4 GX35 • IGNITION COIL REASSEMBLY: Clean the tapered part of dirt, oil, grease and other foreign material before installation. 1) Be sure that the woodruff key is set in the key groove properly. 2) Holding the flywheel with a commercially available strap wrench, tighten the 8 mm flange nut to the specified torque. TORQUE: 22.6 N·m (2.3 kgf·m, 16.6 lbf·ft) STRAP WRENCH (Commercially available) Attach one lead of the tester to the lead terminal and another tester lead to the iron core, and measure the primary resistance of the ignition coil. b. INSPECTION Resistance 0.75 – 0.92 Ω Attach one lead of the tester to the terminal inside the spark plug cap and another lead to the iron core, and measure the secondary resistance of the ignition coil. Resistance 6.1 – 9.3 kΩ • CLUTCH ASSEMBLY Measure the thickness at the center of the clutch lining. Standard Service limit 2.0 mm (0.08 in) 1.0 mm (0.04 in) 8 mm FLANGE NUT *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 7-4 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. 7-4 GX35 • IGNITION COIL REASSEMBLY: Clean the tapered part of dirt, oil, grease and other foreign material before installation. 1) Be sure that the woodruff key is set in the key groove properly. 2) Holding the flywheel with a commercially available strap wrench, tighten the 8 mm flange nut to the specified torque. TORQUE: 22.6 N·m (2.3 kgf·m, 16.6 lbf·ft) STRAP WRENCH (Commercially available) Attach one lead of the tester to the lead terminal and another tester lead to the iron core, and measure the primary resistance of the ignition coil. b. INSPECTION Resistance 0.75 – 0.92 Ω Attach one lead of the tester to the terminal inside the spark plug cap and another lead to the iron core, and measure the secondary resistance of the ignition coil. Resistance 6.1 – 9.3 kΩ • CLUTCH ASSEMBLY Measure the thickness at the center of the clutch lining. Standard Service limit 2.0 mm (0.08 in) 1.0 mm (0.04 in) 8 mm FLANGE NUT *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 7-4 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. consulab.com info@consulab.com 23 91-EM-045-HN04 SA-5 - Level II — Valve Clearance Adjustment SA-5 - Level II — Valve Clearance Adjustment Instructor Notes Teaching Suggestions • Use hot vs. cold examples: Emphasize how thermal expansion affects valve clearance. Help students understand that a clearance set too tight when cold can prevent valves from fully closing at operating temperature. • Connect symptoms to causes: Have students relate: - Tight lash → loss of compression, misfires, burnt valves - Excessive lash → noise, reduced lift, poor airflow, increased wear • Relate lash to timing and airflow: Reinforce that valve clearance affects valve opening/closing timing, lift, and dura- tion, not just noise. • Frame it as durability protection: Present valve lash as a controlled safety gap. Too loose causes impact loading and wear, while too tight leads to overheating and valve damage. • Model proper measurement technique: Demonstrate correct feeler gauge use (slight drag feel, correct blade selec- tion, measuring at proper cam position). • Reinforce TDC accuracy: Ensure students understand why measurements must be taken at the correct TDC position to avoid incorrect readings. Practical Applications • Real-world service: Connect valve clearance checks to maintenance on small engines, motorcycles, and Honda en- gines where periodic adjustment is required. • Customer complaints: Relate valve clearance conditions to common issues: - Ticking noise → excessive clearance - Hard start/no-start → tight clearance - Low power/rough running → incorrect lash • Diagnostic thinking: Encourage students to differentiate between timing issues vs. valve clearance issues when diag- nosing engine problems. • Use of service data: Stress that technicians rely on manufacturer specifications and procedures, not estimation. • Verification of work: Highlight the importance of rechecking clearance after adjustment and confirming proper torque on locknuts. Why Modern Engines Still Use Adjustable Valve Lash • Improved high RPM stability (no hydraulic lifter pump-up) • More precise control of valve timing events • Better durability under high load and high temperature conditions • Reduced design complexity in certain engine applications consulab.com info@consulab.com 24 91-EM-045-HN04 SA-5 - Level II — Valve Clearance Adjustment Answers Objective: Measure and adjust valve clearance and evaluate its effect on engine performance Material Required: EM-045-HN04, Honda manufacturer specifications, feeler gauges, torque wrench Part 1 – Valve Component Identification Match each component name to the numbered identifier on the diagram. Use the glossary as needed. Word Bank : Exhaust valve spring retainer, Intake rocker arm, Intake Camshaft, Spark plug, Exhaust Valve spring, Intake Valve spring, Valve seal, Exhaust Rocker arm, Exhaust port, Locking nut, Cylinder Head, Intake valve spring retainer, Adjuster, Exhaust Camshaft © Honda Motor Co. 2. CYLINDER BLOCK/VALVES a. DISASSEMBLY/REASSEMBLY 1. Remove the head cover and cam pulley (P. 8-1). 2. Remove the lower crankcase (P. 8-5). 3. Remove the crankshaft (P. 9-1). 4 5 7 3 1 8 9 10 14 11 12 6 13 2 1. Spark plug 2. Intake Valve spring 3. Intake Rocker arm 4. Intake valve spring retainer 5. Exhaust valve spring retainer 6. Valve seal 7. Exhaust Valve spring 8. Exhaust Rocker arm 9. Adjuster 10. Locking nut 11. Exhaust Camshaft 12. Intake Camshaft 13. Cylinder Head 14. Exhaust port consulab.com info@consulab.com 25 91-EM-045-HN04 SA-5 - Level II — Valve Clearance Adjustment Part 2 – Valve Clearance Did You Know? A shim is a small metal disc used to adjust clearance, and a bucket is the component that sits over the valve and is pushed by the cam. The EM-045 has neither. It is a screw and locknut design. Valve clearance (lash) is the small gap between the cam and the valve that allows for expansion as engine parts heat up, and it is measured in millimeters (mm) or thousandths of an inch (in.). As the engine heats up, the valves, cylinder head, and camshaft components expand, making this clearance necessary for proper opera- tion. If the clearance is too tight, valves may remain slightly open at operating tem- perature, causing loss of compression, misfires, and overheating of the valve face, which can lead to burnt valves due to poor heat transfer through the seat. Excessive clearance, on the other hand, causes delayed valve opening and early closing, reducing valve lift and duration, which negatively affects airflow, engine performance, and efficiency, while also increasing noise and wear from impact loading in the valvetrain. Impact of Valve Clearance on Engine Performance Condition Performance Too Loose Noisy operation, reduced performance, increased wear Within Specification Valve opens/closes correctly, good seal, optimal performance Too Tight Valve may not fully close, loss of compression, possible valve damage Checking Valve Clearance Follow the procedure below to inspect the EM-045 valve clearance. NOTE: Valve clearance inspection and adjustment must be performed with the engine cold. Step 1: Remove top head cover 3-4 GX35 4) Visually inspect the spark plug. Discard the plug if the insulator is cracked or chipped. 5) Measure the plug gap with a wire-type feeler gauge. If necessary, adjust the gap by bending the side electrode. 6) Make sure the sealing washer is in good condition; replace the plug if necessary. 7) Install the plug fingertight to seat the washer, then tighten with a plug wrench (an additional 1/2 turn if a new plug) to compress the sealing washer. If you are reusing a plug, tighten 1/8-1/4 turn after the plug seats. A loose spark plug can become very hot and can damage the engine. Overtightening the spark plug can damage the threads in the engine. NOTICE Valve clearance inspection and adjustment must be performed with the engine cold. 1) Remove the 5 x 14 mm top cover bolt and remove the top cover. 2) Remove the two 5 x 12 mm hex bolt from the head cover. • Engine oil can leak out when removing the head cover. Catch the leaking oil with a suitable material and wipe up the area immediately. Inspection/Adjustment: 5. VALVE CLEARANCE GAP 0.6 – 0.7 mm (0.024 – 0.028 in) 5 x 14 mm TOP COVER BOLT TOP COVER SIDE ELECTRODE HEAD COVER 5 x 12 mm HEX BOLT (2) Standard spark plug CMR5H (NGK) Spark plug gap 0.6 - 0.7 mm (0.024 -0.028 in) ENGINE ASSEMBLY *GX35(E)_SEC.01-06 9/14/04 4:32 PM Page 3-4 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. Step 2: Rotate engine to Top Dead Center (TDC). 3-5 GX35 Date of Issue: October, 2004 © Honda Motor Co., Ltd. 4) Insert a feeler gauge between the rocker arm and valve to measure the valve clearance. 5) If adjustment is necessary proceed as follows: a. Loosen the adjusting screw lock nut and adjust the valve clearance by turning the adjusting screw right or left. b. Holding the adjusting screw with the tappet adjusting wrench, tighten the lock nut to the specification. TORQUE: 4.9 N·m (0.5 kgf·m, 3.9 Ibf·ft) c. After tightening the lock nut recheck the valve clearance. Standard valve clearance IN 0.08 ± 0.02 mm EX 0.11 ± 0.02 mm 3) Set the piston at top dead center of the compression stroke. Align the “ ” mark on the cam pulley with the cylinder head center. Start the engine and allow it to warm up to normal operating temperature. Then, adjust the idle speed by turning the throttle stop screw right or left. Idle speed adjustment: Loosen the fuel tank cap and release the pressure from the tank before operation. 1) Drain the fuel tank and remove the recoil starter (P. 6-1). 2) Remove the fuel tank. Cleaning: 6. CARBURETOR 7. FUEL TANK/FUEL FILTER ADJUSTING SCREW CYLINDER HEAD CENTER ALIGNMENT MARK THROTTLE STOP SCREW To increase valve clearance, screw out. To decrease valve clearance, screw in. FUEL TANK Standard idle speed 3,100 ± 200 rpm Gasoline is highly flammable and explosive. You can be burned or seriously injured when handling fuel. • Keep heat, sparks, and flame away. • Handle fuel only outdoors. • Wipe up spills immediately. ADJUSTING SCREW LOCK NUT FEELER GAUGE *GX35(E)_SEC.01-06 9/14/04 4:32 PM Page 3-5 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. Step 3: Insert the feeler gauge be- tween the rocker arm and valve spring 3-5 GX35 Date of Issue: October, 2004 © Honda Motor Co., Ltd. 4) Insert a feeler gauge between the rocker arm and valve to measure the valve clearance. 5) If adjustment is necessary proceed as follows: a. Loosen the adjusting screw lock nut and adjust the valve clearance by turning the adjusting screw right or left. b. Holding the adjusting screw with the tappet adjusting wrench, tighten the lock nut to the specification. TORQUE: 4.9 N·m (0.5 kgf·m, 3.9 Ibf·ft) c. After tightening the lock nut recheck the valve clearance. Standard valve clearance IN 0.08 ± 0.02 mm EX 0.11 ± 0.02 mm 3) Set the piston at top dead center of the compression stroke. Align the “ ” mark on the cam pulley with the cylinder head center. Start the engine and allow it to warm up to normal operating temperature. Then, adjust the idle speed by turning the throttle stop screw right or left. Idle speed adjustment: Loosen the fuel tank cap and release the pressure from the tank before operation. 1) Drain the fuel tank and remove the recoil starter (P. 6-1). 2) Remove the fuel tank. Cleaning: 6. CARBURETOR 7. FUEL TANK/FUEL FILTER ADJUSTING SCREW CYLINDER HEAD CENTER ALIGNMENT MARK THROTTLE STOP SCREW To increase valve clearance, screw out. To decrease valve clearance, screw in. FUEL TANK Standard idle speed 3,100 ± 200 rpm Gasoline is highly flammable and explosive. You can be burned or seriously injured when handling fuel. • Keep heat, sparks, and flame away. • Handle fuel only outdoors. • Wipe up spills immediately. ADJUSTING SCREW LOCK NUT FEELER GAUGE *GX35(E)_SEC.01-06 9/14/04 4:32 PM Page 3-5 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. 1. Record the valve clearance for both valves in the space below. A. Intake: Answers will vary, see spec below B. Exhaust: Answers will vary, see spec below consulab.com info@consulab.com 26 91-EM-045-HN04 SA-5 - Level II — Valve Clearance Adjustment Checking Manufacturer Specifications 2. Record the Honda specifications for each valve. Were the valve clearances within spec? If not, see section Adjusting Valve Clearances. A. Intake: 0.08 ± 0.02 Within Spec? Y/N B. Exhaust : 0.11 ± 0.02 Within Spec? Y/N 3. What are the torque specifications for the valve locking nuts? 4.9 N-m or 3.9 lBf-ft Adjusting Valve Clearance If adjustment is necessary, proceed as follows: Step. 1: Loosen the adjusting screw lock nut and adjust the valve clearance by turning the adjusting screw right or left. Step 2: Holding the adjusting screw with the tappet adjusting wrench, tight- en the lock nut to the specification using a torque wrench. Part 3 – Valve Clearance Analysis 4. An engine has correct timing marks aligned, but it runs poorly and has low compression. What is the MOST likely cause? A. Valve clearance too tight B. Valve clearance too loose C. Timing belt installed correctly D. Camshaft not rotating 5. What is valve clearance (lash) and why is it required in an OHC engine? A. A gap that increases engine noise and improves airflow B. A gap that allows for component expansion and ensures valves fully close C. A gap that controls fuel delivery timing D. A gap that prevents the camshaft from rotating 6. Explain why the camshaft at the 12 o’clock position indicates Top Dead Center (TDC) instead of relying on the crank- shaft alone. Because the crankshaft rotates twice for every one rotation of the camshaft. The camshaft position shows which stroke the engine is on, making it more accurate for identifying TDC in engine timing. 3-5 GX35 Date of Issue: October, 2004 © Honda Motor Co., Ltd. 4) Insert a feeler gauge between the rocker arm and valve to measure the valve clearance. 5) If adjustment is necessary proceed as follows: a. Loosen the adjusting screw lock nut and adjust the valve clearance by turning the adjusting screw right or left. b. Holding the adjusting screw with the tappet adjusting wrench, tighten the lock nut to the specification. TORQUE: 4.9 N·m (0.5 kgf·m, 3.9 Ibf·ft) c. After tightening the lock nut recheck the valve clearance. Standard valve clearance IN 0.08 ± 0.02 mm EX 0.11 ± 0.02 mm 3) Set the piston at top dead center of the compression stroke. Align the “ ” mark on the cam pulley with the cylinder head center. Start the engine and allow it to warm up to normal operating temperature. Then, adjust the idle speed by turning the throttle stop screw right or left. Idle speed adjustment: Loosen the fuel tank cap and release the pressure from the tank before operation. 1) Drain the fuel tank and remove the recoil starter (P. 6-1). 2) Remove the fuel tank. Cleaning: 6. CARBURETOR 7. FUEL TANK/FUEL FILTER ADJUSTING SCREW CYLINDER HEAD CENTER ALIGNMENT MARK THROTTLE STOP SCREW To increase valve clearance, screw out. To decrease valve clearance, screw in. FUEL TANK Standard idle speed 3,100 ± 200 rpm Gasoline is highly flammable and explosive. You can be burned or seriously injured when handling fuel. • Keep heat, sparks, and flame away. • Handle fuel only outdoors. • Wipe up spills immediately. ADJUSTING SCREW LOCK NUT FEELER GAUGE *GX35(E)_SEC.01-06 9/14/04 4:32 PM Page 3-5 Date of Issue: April 2006 © Honda Motor Co., Ltd. © Honda Motor Co. consulab.com info@consulab.com 27 91-EM-045-HN04 SA-5 - Level II — Valve Clearance Adjustment 7. Fill in the blank. In a four-stroke internal combustion engine, the intake valve is manufactured to be larger than the exhaust valve in order to maximize the volume of air and fuel that enters the combustion chamber. 8. List one problem caused by too much valve clearance. Excessive valve clearance can cause noise, reduced performance, and/or increased wear. consulab.com info@consulab.com 28 91-EM-045-HN04 SA-6 - Level I — Spark Plug Adjustment SA-6 - Level I — Spark Plug Adjustment Instructor Notes Teaching Suggestions • Emphasize cause-and-effect by having students intentionally change spark plug gap and predict how each condition would affect starting, power, and emissions. • Reinforce proper tool use by demonstrating correct measurement with a wire-type gap gauge and adjusting only the ground electrode. • Guide students to use manufacturer information, showing that spark plug gap and torque specifications are found in the ConsuLab operation manual and/or Honda specifications. • If available, show multiple spark plug examples (hot vs. cold) so students can visually compare insulator cone length and connect design to heat range. Include a damaged spark plug example (cracked or chipped insulator) to reinforce inspection criteria and when a plug must be discarded. Practical Applications • Have students treat gap changes as a diagnostic test, not just an adjustment. Ask them to connect each gap condi- tion to real symptoms like low power, emissions, misfires, or hard starting. • Reinforce that proper gap is a balance, helping students understand why technicians do not simply make the gap smaller or larger to “fix” a problem. • Connect the activity to real shop practice by explaining that spark plug gap is often checked or corrected during diagnostics, not just during routine maintenance. Optional Extension Activity If a digital multimeter is available, students can measure the resistance of the spark plug from the terminal to the center electrode. This test checks the internal resistor, which is designed to reduce electrical interference. A spark plug with an open circuit or incorrect resistance may cause ignition issues and should be replaced. Great opportunity to show the resistance of bad spark plugs here if you have them as well. consulab.com info@consulab.com 29 91-EM-045-HN04 SA-6 - Level I — Spark Plug Adjustment Answers Objective: Identify, inspect, and correctly gap a spark plug and relate its adjustment to engine performance. Material Required: EM-045-HN04, spark plug socket, ratchet, device with internet Part 1 – Spark Plug Basics A spark plug is a precision ignition component designed to deliver electrical energy into the combustion chamber to ignite the air-fuel mixture at exactly the right moment. The terminal is the top connection point of the spark plug where high voltage from the ignition coil or spark plug wire enters the plug. This electrical energy travels through the internal resistor, which helps suppress electromagnetic interference that could affect vehicle electronics and ignition perfor- mance while also stabilizing spark energy. The voltage then moves through the center core (conductor), which carries the electrical current down the center of the plug to the firing tip. Surrounding this conductor is a ceramic insulator, usually made from strong aluminum oxide. It keeps the high-voltage center conductor electrically separated from the metal shell and also helps move heat from the firing end into the cylinder head. The metal shell forms the structural body of the spark plug, allowing it to be thread- ed securely into the cylinder head while also acting as a heat transfer path to help control plug operating temperature. The threads on the shell ensure proper mounting, sealing, and heat transfer between the spark plug and engine. Near the threaded area is the gasket or sealing seat, which prevents combustion gases from leaking past the spark plug and maintains cylinder compression. At the lower end of the plug is the center electrode, which receives the high voltage and serves as the point where elec- trical energy concentrates before jumping the spark gap. This center electrode also passes through the insulator cone that can determine the heat range of the spark plugs performance. Opposite the center electrode is the ground electrode, attached to the shell, which provides the return path to ground for the electrical circuit. The small space between the center and ground electrode is known as the spark gap, and this is where the spark occurs, igniting the compressed air-fuel mixture. Each spark plug has an identifying code that shows its size, design, and heat range. The heat range controls how fast heat is removed from the plug tip. A plug that is too hot can cause pre-ignition and engine damage. A plug that is too cold can foul and cause misfires. The code also includes thread size, reach, seat type, electrode design, and resistor use. Spark plug reach is the length of the threaded portion of the spark plug, measured from the sealing surface to the end of the threads. It determines how far the spark plug extends into the cylinder head and combustion chamber. Using the wrong spark plug can cause poor sealing, incorrect spark location, or mechanical damage. The code ensures the spark plug matches the engine’s design and operating conditions. Terminal Insulator Resistor Core Shell Threads Insulator Cone Center Electrode Ground Electrode consulab.com info@consulab.com 30 91-EM-045-HN04 SA-6 - Level I — Spark Plug Adjustment The heat range of a spark plug controls how fast heat moves away from the plug’s tip into the cylinder head. This affects engine performance and reliability. A hot plug holds more heat at the tip, which helps burn off carbon deposits in cooler or low-load engines. If it gets too hot, it can cause pre-ignition or detonation and damage engine parts. A cold plug removes heat quickly, which is better for high-load or high-performance engines. If it runs too cool, carbon can build up and cause misfires. Hot plugs have longer insula- tor cones to hold heat, while cold plugs have shorter insulator cones to remove heat faster, but the spark plug code is the only reliable way to identify heat range. The goal is to keep the plug tip in the right temperature range, so it stays clean without overheating. Spark Plug Codes Decoded Shell Construction R Heat Thread reach A - 18mm x 1 AB - 18mm x 13/16 B - 14mm x 13/16 BC - 14mm x 13/16 BK - 14mm x 5/8 C - 10mm x 5/8 D - 12mm x 18.0mm DC - 12mm x 5/8 E - 8mm x 13mm G - PFI/2 Pipe x 23 L - Compact Type M - Cmpact Type B P - Projected Isulator U - Semi Surface Z - Inductive Resistor R E S I S T O R 2 4 5 6 7 8 8.5 9 9.5 10 10.5 11 12 E- 19mm x 3/4 EH - 19mm x 3/4 H - 12.7mm x 1/2 B - 14mm x 13/16 L - 11.2mm x 7/16 Example B L R 9 E H O T C O L D 1. What could happen if a spark plug is too hot or too cold for an engine? If a spark plug is too hot, it can overheat and cause pre-ignition or engine damage. If a spark plug is too cold, it may not burn off carbon, which can cause fouling, misfires, and poor engine performance. 2. In the example code above, what is the thread reach? 19mm x ¾ consulab.com info@consulab.com 31 91-EM-045-HN04 SA-6 - Level I — Spark Plug Adjustment Part 2 – Identifying a Spark Plug 3. Remove the spark plug from the engine using the supplied ratchet and socket. Record the spark plug code in the boxes below, then use the Spark Plug Codes Decoded table to identify what each letter/number of the code means. Shell is 10mm x 5/8 Heat range of 5Has a resistor Compact Type B Construction 12.7mm x ½ Thread reach C M R 5 H 4. Circle one. The spark plug that removes heat from the tip more quickly is a hot plug / cold plug. 5. Circle one. According to the spark plug code, the EM-045 spark plug would be considered a hot plug / cold plug, therefore, it must have a shorter / longer insulator cone. 6. Circle one. The lower / higher the heat range number, the hotter the spark plug. Part 3 – Spark Plug Gap A spark plug must have the correct spark gap so the spark forms properly and combustion happens efficiently. The size of the gap affects how much voltage is needed to fire the plug and how strong the spark will be. If the spark plug gap is too wide, more voltage is needed to jump the gap. This makes the ignition system work harder and can cause misfires, hard starting, or problems under load when cylinder pressure is high. If the gap is too narrow, the spark happens more easily but is weaker. A weak spark can create a small flame, leading to poor combustion, less power, higher emissions, and carbon fouling. Remove the spark plug from the engine using the proper socket and ratchet. Visually inspect the spark plug insulator. If the insulator is cracked or chipped, discard the plug and replace it with a new one. Proceed with a usable spark plug. 7. Using a wire-type spark plug gauge or feeler gauge, measure the current spark plug gap: Answers will vary in /mm. 8. Adjust the spark plug gap to 0.032 in (0.8 mm) by carefully bending only the ground electrode. Gap verified with spark plug gapper Yes ☐ No 9. Adjust the spark plug gap to 0.020 in (0.5 mm). Gap verified with spark plug gapper Yes ☐ No 10. Which gap setting would require more ignition voltage to fire? 0.032 in ☐ 0.020 in consulab.com info@consulab.com 32 91-EM-045-HN04 SA-6 - Level I — Spark Plug Adjustment 11. Which gap would create a smaller, weaker spark? ☐ 0.032 in 0.020 in 12. Using the manufacturer and spark plug code on the plug, find the manufacturer’s spark plug specifications and record them: A. Minimum gap: 0.024 in (0.6 mm) B. Maximum gap: 0.028 in (0.7 mm) C. Adjust the spark plug gap to this specification. D. Spark plug torque specification: 11.8 Nm / 8.7 lb-ft 13. An engine runs but has low power and higher emissions. Which condition is more likely? ☐ Gap too wide Gap too narrow Explain your choice: A gap that is too narrow creates a weaker spark. This can lead to poor combustion, which reduces engine power and increases emissions. 14. A vehicle has hard starting and misfires under load. Should the spark plug gap be increased or decreased? Why? The spark plug gap should be decreased because a gap that is too wide can cause misfires and hard starting, espe- cially under load. consulab.com info@consulab.com 33 91-EM-045-HN04 SA-7 - Level III — Piston Ring End Gap Adjustment SA-7 - Level III — Piston Ring End Gap Adjustment Instructor Notes Teaching Suggestions • Begin with a brief review of piston components using a physical piston or diagram, emphasizing how the rings, grooves, and cylinder work together for sealing and oil control. • Demonstrate correct use of a feeler gauge for both side clearance and end gap, focusing on proper technique (light drag, correct positioning, and not forcing the blade). • Model proper ring removal and handling to prevent damage, reinforcing that only the compression rings are re- moved during this activity. • Demonstrate correct vs. incorrect ring gaps (too tight vs. too large) using visual aids or a cutaway engine to help students connect measurements to real failure modes. • Encourage students to refer back to the manufacturer’s specifications and have them available for use. • Use feeler gauges to measure piston ring end gap in a real cylinder bore and compare results to manufacturer spec- ifications. Practical Applications • Measure piston ring side clearance on an actual piston and relate findings to proper sealing and ring movement. • Have students file-fit piston rings (if available) to achieve correct end gap and observe the impact of precision ad- justments. • Demonstrate improper clearances (too tight vs. too loose) if possible, to visualize risks such as scuffing, sticking, and blow-by. • Perform a compression test and connect low readings to excessive piston ring end gap and leakage. • Use a heated ring or expansion demo to show how thermal growth affects clearances during engine operation. • Apply measurement results to real diagnostic scenarios, determining whether rings should be reused or replaced based on specifications. Optional Extension, micrometer required Introduce and demonstrate the micrometer (not included), explaining how it is used to measure piston ring thickness and why precision measurement is critical. consulab.com info@consulab.com 34 91-EM-045-HN04 SA-7 - Level III — Piston Ring End Gap Adjustment Answers Objective: Measure piston ring end gap and side clearance, then compare to specifications to evaluate engine condition. Material Required: EM-045-HN04, manufacturer specifications Part 1 – Piston Component Identification A piston is made up of several important parts that work together to seal the combustion chamber and control oil. The piston head (crown) is the top surface that is exposed to combustion pressure. Just below it are the ring land grooves, which hold the piston rings in place. The compression rings (top rings) seal combustion gases and transfer heat to the cylinder wall, while the oil control ring regulates oil on the cylinder wall to prevent excess oil from entering the combus- tion chamber. The piston skirt is the lower portion of the piston that helps guide it smoothly in the cylinder and maintain alignment. One critical feature of piston rings is the small gap between the ends of the ring, known as the piston ring end gap, which is essential for proper engine operation. Word Bank : Oil Control Ring, Piston Head, Compression Ring, Compression Ring, Ring Land Grooves, Piston Skirt Piston Skirt Ring Land Grooves Piston Head Oil control Ring Compression Ring Compression Ring consulab.com info@consulab.com 35 91-EM-045-HN04 SA-7 - Level III — Piston Ring End Gap Adjustment Part 2 – Key Piston Measurements Piston ring end gap is the small, intentional clearance between the two ends of a piston ring when it is installed inside the cylinder bore. When the ring is compressed into the cylinder, the ends do not touch. This gap allows for thermal ex- pansion as the engine reaches operating temperature. Without this clearance, the ring ends could butt together as they expand, causing severe engine damage. To measure piston ring end gap, the ring is placed inside the cylinder bore (not on the piston) and squared up using a piston or ring squaring tool to ensure it sits perfectly level in the bore. A set of feeler gauges is then inserted between the ring ends to measure the gap. This measurement is typically taken at a specified depth in the cylinder (often near the top or at multiple points) to check for bore wear or taper. The measured gap is then compared to manufacturer specifi- cations, which vary depending on engine design, bore size, and application (naturally aspirated vs. performance engines). The importance of correct piston ring end gap cannot be overstated. If the gap is too tight, the ring ends can expand and make contact under heat, leading to scuffing, cylinder wall damage, or even piston failure. If the gap is too large, it can result in poor sealing, causing loss of compression, reduced engine efficiency, increased blow-by, and higher oil con- sumption. Proper end gap ensures optimal sealing, heat transfer, and long-term durability of the engine. In addition to the gap between the ends of the ring, there is also piston side clearance, which is the space between the piston ring and the groove wall. This clearance allows the ring to move freely, helps maintain a proper seal, and prevents the ring from sticking in the groove. Side clearance is typically measured using a feeler gauge inserted between the ring and the groove wall. Measuring Piston Ring Side Clearance Before removing the compression rings from the piston assembly measure and record the piston ring side clearance. Remember to check the manufacturer’s specifications. 1. What is the purpose of measuring the side ring clearance? The purpose of measuring side ring clearance is to make sure the piston ring can seal properly and move freely in the groove without sticking. 2. What tool is used to measure the gap between the ring and groove wall? A feeler gauge 3. Record the manufacturer’s specifications of the piston ring side clearance in the space below: Standard: 0.015 – 0.056 (0.0006 – 0.0022) Service limit: 0.120 (0.0047) 4. Measure the ring side clearance of the EM-045: Top Ring Circle: PASS / FAIL Second Ring Circle: PASS / FAIL © Honda Motor Co. 9-6 GX35 • PISTON-TO-CYLINDER CLEARANCE • PISTON SKIRT O.D. Measure and record the piston O.D. at a point 10 mm (0.39 in) from the bottom of the skirt and 90° to the piston pin bore. X Y 10 mm (0.39 in) 3 INSPECTION • CYLINDER SLEEVE I.D. Measure and record the cylinder I.D. at three levels in both the “ X ” axis (perpendicular to crankshaft) and the “ Y ” axis (parallel to crankshaft). Take the maximum reading to determine cylin- der wear and taper. Standard Service limit 38.970 – 38.990 mm (1.534 – 1.535 in) 38.900 mm (1.5314 in) • PISTON RING SIDE CLEARANCE When any piston ring exceeds the service limit, replace all the piston rings as a set. Standard Service limit 39.000 – 39.015 mm (1.535 – 1.536 in) 39.100 mm (1.5393 in) Standard Service limit 0.010 – 0.045 mm (0.0004 – 0.0018 in) 0.120 mm (0.0047 in) • PISTON RING WIDTH Top/Second Standard 0.970 – 0.990 mm (0.0382 – 0.0390 in) Service limit 0.920 mm (0.0362 in) Top/Second Standard 0.015 – 0.056 mm (0.0006 – 0.0022 in) Service limit 0.120 mm (0.0047 in) 90° *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 9-6 Date of Issue: April 2006 © Honda Motor Co., Ltd. consulab.com info@consulab.com 36 91-EM-045-HN04 SA-7 - Level III — Piston Ring End Gap Adjustment Measuring Ring End Gap Carefully remove the two top rings from the piston by lifting the ring from the groove and rotate the ring out of the groove without twisting or bending the ring. Remove only the compression rings. Do not remove the oil control ring. 5. Record the manufacturer’s specifications for the piston ring end gap: Standard: 0.10 – 0.25 (0.004 – 0.010) Service limit: 0.60 (0.024) 6. What tool is used to measure piston ring end gap? A feeler gauge Carefully slide the ring into the cylinder as shown and measure the gap on the ring ends between each other. 7. Measure the piston ring gap of the EM-045: Top Ring Circle: PASS / FAIL Second Ring Circle: PASS / FAIL 8. Why is piston ring side clearance measured before ring end gap during engine inspection? Technicians check side clearance first because it determines if the piston and ring are still usable. If the side clear- ance is out of specification, the piston and ring are worn and must be replaced, making further measurements unnecessary. If side clearance is incorrect, the ring may not sit properly in the groove, which can lead to inaccurate ring end gap measurements and incorrect conclusions about engine condition. © Honda Motor Co. 9-7 GX35 • PISTON RING END GAP Put the piston ring in the cylinder and then use the piston crown to push the ring down. This will make the piston ring horizontal so ring end gap can be measured. Because the combination oil rings are used on this model, always replace piston rings as a set. • PISTON PIN O.D. Standard Service limit 7.994 – 8.000 mm (0.3147 – 0.3150 in) 7.950 mm (0.3130 in) • PISTON PIN BORE I.D. Standard Service limit 8.010 – 8.026 mm (0.3154 – 0.3160 in) 8.060 mm (0.3173 in) • PISTON PIN-TO-PIN BORE CLEARANCE Standard Service limit 0.010 – 0.032 mm (0.0004 – 0.0013 in) 0.070 mm (0.0028 in) • CONNECTING ROD SMALL END I.D. Standard Service limit 7.978 – 7.989 mm (0.3141 – 0.3145 in) Replace if exceeding the standard value. Top/Second Standard 0.10 – 0.25 mm (0.004 – 0.010 in) Service limit 0.60 mm (0.024 in) *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 9-7 Date of Issue: April 2006 © Honda Motor Co., Ltd. consulab.com info@consulab.com 37 91-EM-045-HN04 SA-7 - Level III — Piston Ring End Gap Adjustment Optional Extension - Measuring Piston Ring Thickness A properly selected ring thickness ensures correct side clearance between the ring and piston groove. If the ring is too thick, it can bind in the groove as thermal expansion occurs, leading to scuffing or ring breakage. If it’s too thin, exces- sive clearance allows combustion gases to leak past the ring (blow-by), reducing compression and engine efficiency. 1. What tool is used to measure piston ring thickness? Micrometer (not included) 2. Record the specification for the piston ring thickness Piston ring thickness/width: 0.970 – 0.990 (0.0382 – 0.0390) Service Limit: 0.920 (0.0362) 3. Measure each ring and record your findings. Remove only the compression rings. Do not remove the oil control ring. Top Ring Circle: PASS / FAIL Second Ring Circle: PASS / FAIL 4. ANALYSIS A student measures the EM-045 piston rings and records the following: Top ring: thickness 0.995, side clearance 0.008, end gap 0.18 Second ring: thickness 0.925, side clearance 0.070, end gap 0.62 Using the specifications above, determine which ring(s) pass/fail and predict which engine problem would most likely happen first when the engine reaches operating temperature (ring sticking/scuffing vs. blow-by/loss of compression) and why. Your explanation must connect ring thickness to side clearance, end gap, and thermal expansion. Then state the best corrective action. Both rings fail. The top ring is too thick and has too little side clearance, so as the engine heats up and the ring expands, it will likely bind in the groove, causing sticking or scuffing first. The second ring has excessive end gap beyond the service limit, which would cause blow-by and loss of compression. The best corrective action is to re- place both compression rings with the correct specifications and inspect/clean the piston grooves, then recheck all clearances. © Honda Motor Co. 9-6 GX35 • PISTON-TO-CYLINDER CLEARANCE • PISTON SKIRT O.D. Measure and record the piston O.D. at a point 10 mm (0.39 in) from the bottom of the skirt and 90° to the piston pin bore. X Y 10 mm (0.39 in) 3 INSPECTION • CYLINDER SLEEVE I.D. Measure and record the cylinder I.D. at three levels in both the “ X ” axis (perpendicular to crankshaft) and the “ Y ” axis (parallel to crankshaft). Take the maximum reading to determine cylin- der wear and taper. Standard Service limit 38.970 – 38.990 mm (1.534 – 1.535 in) 38.900 mm (1.5314 in) • PISTON RING SIDE CLEARANCE When any piston ring exceeds the service limit, replace all the piston rings as a set. Standard Service limit 39.000 – 39.015 mm (1.535 – 1.536 in) 39.100 mm (1.5393 in) Standard Service limit 0.010 – 0.045 mm (0.0004 – 0.0018 in) 0.120 mm (0.0047 in) • PISTON RING WIDTH Top/Second Standard 0.970 – 0.990 mm (0.0382 – 0.0390 in) Service limit 0.920 mm (0.0362 in) Top/Second Standard 0.015 – 0.056 mm (0.0006 – 0.0022 in) Service limit 0.120 mm (0.0047 in) 90° *GX35(E)_SEC.07-10 9/15/04 2:32 PM Page 9-6 Date of Issue: April 2006 © Honda Motor Co., Ltd. consulab.com info@consulab.com 38 91-EM-045-HN04 SA-8 Level I Engine Reassembly SA-8 Level I Engine Reassembly Instructor Notes Teaching Suggestions • Consider checking students’ work before the crankcase and rocker cover are secured. This allows verification of correct orientation, seal placement, and timing setup while components are still visible and prevents hidden errors that are difficult to diagnose later. • Use this checklist as a peer inspection tool. Assign one student as the assembler and a second student as the in- spector. The inspector completes the checklist, verifies torque values, and signs the QA/QC section. This reinforces professional inspection habits and helps students learn from one another’s work. • Gamify the rebuild and inspection process. To increase engagement, consider running this assignment as a friendly competition where teams are judged by peers using the checklist criteria. Practical Applications • Although the EM-045 engine is compact, the reassembly process mirrors the same principles used when rebuilding larger engines. Skills practiced here directly transfer to automotive engines, such as: - 4-cylinder passenger car engines - Motorcycle and powersports engines - Small diesel or industrial engines - Agricultural and landscaping equipment engines • This checklist reflects real shop practices where technicians must verify component orientation, confirm torque application, and document work before an engine is approved for operation consulab.com info@consulab.com 39 91-EM-045-HN04 SA-8 Level I Engine Reassembly Answers Objective: Inspect and document correct engine assembly per manufacturer specifications. Material Required: EM-045-HN04, Operation Manual, Tool Case of Tools Part 1 – Internal Engine Reinstallation A. Valves & Valve Train ☐ Intake and exhaust valves installed in correct locations without damage ☐ Intake valve seal reinstalled correctly ☐ Valve springs reinstalled correctly ☐ Valve spring retention verified Valve adjustment nut torqued to: 4.9 Nm Notes: B. Piston Assembly ☐ Top ring, compression ring, and oil control rings installed correctly ☐ No damaged or bent rings ☐ Piston arrow oriented correctly ☐ Piston reinstalled smoothly without binding Notes: Piston arrow facing “passenger side” or 3 o’clock if flywheel is 6 o’clock C. Crankshaft ☐ Crankshaft reinstalled correctly ☐ Crankshaft seals seated correctly in their grooves ☐ Crankshaft rotates smoothly by hand after installation Notes: D. Timing Belt ☐ Timing belt installed with correct orientation ☐ Timing belt routed correctly to cam gear Notes: “HONDA” text facing the piston E. Crankcase Assembly ☐ Crankcase bolts tightened from center outward in star-like pattern Crankcase bolts torqued to: 6.4 Nm Notes: consulab.com info@consulab.com 40 91-EM-045-HN04 SA-8 Level I Engine Reassembly Part 2 – Timing Components A. Timing Belt & Flywheel Installation ☐ Timing belt engagement confirmed by rotating camshaft ☐ Flywheel reinstalled with key slot aligned ☐ Flywheel arrow aligned ☐ Cam gear arrow aligned ☐ Timing belt installed on cam gear Flywheel nut torqued to: 22.6 Nm Notes: Flywheel alignment to bolt hole at 6 o’clock and cam gear aligned at 12 o’clock B. Valve Clearance Check Measured Valve Clearance: Answers will vary Notes: C. Rocker Cover Installation Rocker cover bolts torqued to: 6.4 Nm Notes: Part 3 – Exhaust and Intake A. Exhaust / Muffler Assembly ☐ Exhaust / muffler reinstalled correctly ☐ All screws and nuts reinstalled and secure Exhaust mounting bolts torqued to: 4.4 Nm Notes: B. Intake / Carburetor Assembly ☐ Intake / carburetor reinstalled correctly ☐ Hose reinstalled correctly with clamps secure ☐ Fuel filter reinstalled ☐ Fuel filter cover reinstalled Carburetor bolts torqued to: 4.9 Nm Notes: smaller end of hose on top consulab.com info@consulab.com 41 91-EM-045-HN04 SA-8 Level I Engine Reassembly Part 4 – Ignition and Starter A. Spark Plug ☐ Spark plug inspected and reinstalled ☐ Spark plug gap checked / adjusted as needed ☐ Spark plug boot secure Measured Gap: 0.024 in - 0.028 in (0.6 mm -0.7 mm) Spark plug torqued to 11.8 Nm Notes: B. Pull Starter ☐ Pull starter installed correctly Mounting bolts torqued to: 6.4 Nm Notes: C. ON/OFF Switch & Ignition Coil ☐ ON/OFF switch reinstalled ☐ Ignition coil reinstalled ☐ Ignition wire reconnected to ON/OFF switch ☐ Ignition coil air gap checked/adjusted as needed Ignition coil torqued to: 3.4 Nm Measured Gap: 0.2 – 0.4 mm (0.008 – 0.016 in) Notes: Part 5 – Final Assembly A. Safety Covers ☐ Exhaust cover reinstalled ☐ Flywheel cover reinstalled Safety cover bolts torqued to: 6.4 Nm Notes: B. Fluids ☐ Engine oil added ☐ Fuel added Amount of oil added: 100cc Oil type: 10W-30 Amount of fuel added: 60mL Fuel Type: Unleaded gasoline, min. 87 octane Notes: C. Mounting ☐ Engine mounted to stand ☐ Fuel tank reinstalled and connected Notes: QAQC Sign-Off I verify that all listed reassembly inspection steps have been completed and documented. Assembler Name: Signature: Inspector Name: Signature consulab.com info@consulab.com 42 91-EM-045-HN04 Engine Fundamentals Assessment Engine Fundamentals Assessment 1. Which component is responsible for mixing air and fuel before it enters the engine? A. Ignition coil B. Carburetor C. Flywheel D. Crankshaft 2. Which component belongs to the valvetrain system and directly controls valve movement? A. Rocker arm B. Flywheel C. Timing belt D. Carburetor 3. What is the primary role of the connecting rod in engine operation? A. To regulate oil flow inside the crankcase B. To link piston movement to crankshaft rotation C. To keep the piston centered in the cylinder D. To control valve opening and closing 4. During engine teardown, bolts are organized by length and location. Why is this practice important during reassembly? A. Bolt material changes based on engine temperature B. Bolt placement affects ignition timing C. All bolts require the same torque, but length helps identify them D. Incorrect bolt length can damage components or prevent proper assembly 5. Which action best supports correct engine reassembly and longterm performance? A. Tightening fasteners until resistance is felt B. Reinstalling parts in any order once cleaned C. Using a torque wrench on specified fasteners D. Completing valve adjustment before timing is set consulab.com info@consulab.com 43 91-EM-045-HN04 Engine Fundamentals Assessment 6. While reinstalling the timing belt, the timing marks do not line up. What engine issue is most likely if the engine is operated in this condition? A. Reduced oil pressure B. Incorrect valve and piston timing C. Weak ignition spark D. Excessive engine vibration 7. After the timing belt is installed, which verification step best supports confidence that cam-to-crank alignment is correct before finishing assembly? A. Measure valve clearance immediately without rotating the engine B. Install the flywheel nut to maximum tightness to lock timing in place C. Check only the timing belt tension; marks are optional once installed D. Rotate the engine two full revolutions and recheck that timing marks align 8. What is the function of the timing belt in a four-stroke overhead cam engine? A. It transfers rotation from the flywheel to the oil pump B. It synchronizes crankshaft and camshaft rotation C. It controls spark timing electronically D. It reduces rotational vibration 9. A flywheel needs to be removed. Technician A states that the flywheel fins should not be pried on and that a fly- wheel puller should be used instead. Technician B states that prying on the flywheel fins is acceptable if done care- fully. Which technician is correct? A. Tech A only B. Tech B only C. Both Tech A and Tech B D. Neither Tech A nor Tech B 10. Valve clearance is measured and found to be too small. What is the most likely effect on engine operation? A. Reduced lubrication to moving parts B. Excessive spark plug wear C. Increased flywheel inertia D. Valves may not fully close consulab.com info@consulab.com 44 91-EM-045-HN04 Glossary Glossary consulab.com info@consulab.com 45 91-EM-045-HN04 Glossary Glossary Air Filter: A component that removes dust and debris from incoming air before it enters the carburetor, protecting the engine and supporting proper combustion. Bottom dead center (BDC): The lowest point that the piston reaches in the cylinder during its downward movement. Camshaft: A shaft with lobes that opens and closes the engine’s valves at the correct time. Carburetor: A device that mixes air and fuel in the correct ratio before it enters the engine. Carburetor fuel line (Fuel supply line): A hose that delivers fuel from the fuel tank to the carburetor. Ceramic insulator: The non-conductive material inside a spark plug that supports and isolates the center electrode. Center electrode: The central metal rod in a spark plug that carries high voltage to create a spark. Cold plug: A spark plug with a lower heat range that transfers heat away quickly, reducing the risk of overheating. Compression ring: A piston ring that seals combustion pressure and helps transfer heat to the cylinder wall. Connecting rod: A rigid link that connects the piston to the crankshaft and transfers motion between them. Core (spark plug): The internal conductive material of the spark plug that carries electrical current from the terminal to the center electrode. Counterbalance: A weighted engine component designed to reduce vibration caused by rotating and moving parts. Crankcase: The lower part of the engine that houses the crankshaft and contains the engine’s oil system. Crankshaft: A rotating shaft that converts the up-and-down motion of the piston into rotational motion. Crank throw: The offset part of the crankshaft that the connecting rod attaches to, allowing piston movement to create rotation. Cylinder: The round chamber in the engine where the piston moves up and down. consulab.com info@consulab.com 46 91-EM-045-HN04 Glossary Cylinder head: The upper part of the engine that contains the valves, combustion chamber, and spark plug. Electromagnetic induction: The process of generating electrical voltage when a changing magnetic field moves across a conductor. Exhaust Valve: A valve that opens to allow burned gases to exit the cylinder. Feeler gauge: A precision measuring tool used to check small gaps, such as valve clearance or ignition coil air gap. Flywheel: A heavy rotating disc that stores energy and helps keep engine speed steady. Flywheel puller: A special tool used to safely remove the flywheel from the crankshaft without damaging engine compo- nents. Four-stroke cycle: The four stages of engine operation: intake, compression, power, and exhaust. Gasket: A sealing material placed between engine parts to prevent fluid or gas leaks. Ground electrode: The metal arm on a spark plug that extends over the center electrode and forms the gap where the spark occurs. Heat range: A rating of a spark plug that indicates how quickly it transfers heat away from the combustion chamber. Hot plug: A spark plug with a higher heat range that retains more heat, helping prevent fouling. Ignition coil: An electrical component that uses electromagnetic induction to convert low voltage, either from a 12-volt system or from a magneto system, into the high voltage needed to create a spark at the spark plug. Ignition coil air gap: The small distance between the ignition coil and the flywheel magnets that affects the strength of the magnetic field and the coil’s ability to generate spark. Ignition timing: The point when the spark plug fires in relation to the piston’s position. Insulator cone: The visible portion of the ceramic insulator inside the combustion chamber, used to help determine spark plug condition. Intake valve: A valve that opens to allow the air-fuel mixture into the cylinder. Internal resistor: A component inside a spark plug that reduces electrical noise and interference. consulab.com info@consulab.com 47 91-EM-045-HN04 Glossary Magneto ignition system: A self-contained ignition system that uses rotating permanent magnets to generate electrical current, which is converted into high voltage by the ignition coil to create a spark at the spark plug. Muffler: A component that reduces engine noise by slowing and directing exhaust gases as they exit the engine. Needle bearing: A bearing that uses small cylindrical rollers to reduce friction, commonly used in the connecting rod. Oil control ring: A piston ring that regulates the amount of oil on the cylinder wall. Oil pump: A mechanical device that circulates oil through the engine to lubricate moving parts. Overhead cam (OHC) engine: An engine design where the camshaft is located above the valves in the cylinder head. Piston: A moving engine component that travels up and down in the cylinder to create compression and power. Piston head (crown): The top surface of the piston that is exposed to combustion pressure. Piston Rings: Metal rings fitted around the piston that seal the combustion chamber, help control oil on the cylinder wall, and transfer heat from the piston to the cylinder. Piston ring end gap: The small space between the ends of a piston ring when installed in the cylinder, allowing for ther- mal expansion. Piston ring side clearance: The space between the piston ring and the groove wall that allows the ring to move freely and maintain a proper seal. Piston ring land grooves: Grooves in the piston that hold and position the piston rings. Piston skirt: The lower portion of the piston that guides it within the cylinder and maintains alignment. Positive crankcase ventilation (PCV) line: A hose that allows pressure and gases to vent from the crankcase back into the intake system. Primary winding: The low-voltage winding of the ignition coil that carries current to create a magnetic field. Recoil starter: A pull-cord starting system that spins the engine to begin operation. Rocker arm: A pivoting lever in the valvetrain that transfers motion from the camshaft to the valve, opening and closing the intake or exhaust valve at the correct time. Rocker cover: A protective cover that encloses the rocker arms and valve components at the top of the engine. consulab.com info@consulab.com 48 91-EM-045-HN04 Glossary Roller bearing: A bearing that reduces friction by using rolling elements instead of sliding surfaces. Secondary winding: The high-voltage winding of the ignition coil where the collapsing magnetic field induces voltage to create the spark at the spark plug. Spark gap: The space between the center electrode and ground electrode where the spark occurs. Spark plug: A component that produces an electrical spark to ignite the air-fuel mixture. Spark plug reach: The length of the threaded portion of the spark plug that extends into the combustion chamber. Stroke: One complete upward or downward movement of the piston in the cylinder. Terminal (spark plug): The top connection point where the ignition coil or spark plug wire attaches. Timing: The relationship between crankshaft and camshaft position, ensuring valves and ignition occur at the correct time. Timing belt: A belt that keeps the crankshaft and camshaft rotating in proper alignment. Timing Marks: Reference marks on engine components that are used to align the crankshaft and camshaft correctly so the valves open and close at the proper time. Top dead center (TDC): The highest point that the piston reaches in the cylinder during its upward movement. Torque Wrench: A hand tool used to tighten fasteners to a specific torque value, so bolts are tightened correctly without being too loose or too tight. Valve bucket (bucket): A cylindrical component in some OHC engines that sits over the valve and transfers camshaft motion directly to the valve. Valve shim (shim): A thin, precisely sized disc used to adjust valve clearance. Valve spring: A spring that closes the valve after it has been opened by the camshaft and rocker arm. Valve clearance: The specified gap between the valve and rocker arm when the valve is closed. consulab.com info@consulab.com 49 91-EM-045-HN04 Manufacturer Specifications Manufacturer Specifications consulab.com info@consulab.com 50 91-EM-045-HN04 Torque Specifications Torque Specifications Item Thread diameter (mm) Torque Values Nm Lb-ft. Lower Crankcase M5 (CT) 6.4 4.7 ConsuLab Covers M5 (CT) 6.4 4.7 Ignition Coil M4 3.4 2.5 Recoil Starter Pulley M6 6.4 4.7 Flywheel M8 22.6 16.6 Valve Adjusting Lock Nut M5 4.9 3.6 Spark Plug M10 11.8 8.7 Muffler M5 (CT) M5 (STUD BOLT) 4.4 3.2 Carburetor M5 4.9 3.6 consulab.com info@consulab.com 51 91-EM-045-HN04 Honda GX35 Specifications Honda GX35 Specifications Part Item Standard Service Limit Engine Idel Speed 3,100 ± 200 rpm - Cylinder Compression 0.95 ± 0.15 MPa (9.7 ± 1.5 kgf/cm²) / 138 ± 22 psi at 2,000 min-1 (rpm) - Cylinder Sleeve I.D. 39.000 – 39.015 (1.535 – 1.536) 39.100 (1.5393) Piston Skirt O.D. 38.970 – 38.990 (1.534 – 1.535) 38.900 (1.5314) Piston-to-cylinder clearance 0.010 – 0.045 (0.0004 – 0.0018) 0.120 (0.0047) Piston pin bore I.D. 8.010 – 8.026 (0.3154 – 0.3160) 8.060 (0.3173) Piston Pin Pin O.D. 7.994 – 8.000 (0.3147 – 0.3150) 7.950 (0.3130) Piston-to-pin bore clearance 0.010 – 0.032 (0.0004 – 0.0013) 0.070 (0.0028) Piston Rings Ring width Top/second 0.970 – 0.990 (0.0382 – 0.0390) 0.920 (0.0362) Side clearance Top/second 0.015 – 0.056 (0.0006 – 0.0022) 0.120 (0.0047) Ring end gap Top/second 0.10 – 0.25 (0.004 – 0.010) 0.60 (0.024) Connecting Rod Small end I.D. 7.978 – 7.989 (0.3141 – 0.3145) - Valve Valve clearance IN 0.08 ± 0.02 EX 0.11 ± 0.02 Stem O.D. IN 3.470 – 3.485 (0.1366 – 0.1372) 3.400 (0.1339) EX 3.435 – 3.450 (0.1352 – 0.1358) 3.380 (0.1331) Guide I.D. 3.500 – 3.518 (0.1378 – 0.1385) 3.560 (0.1402) Stem-to-guide clearance IN 0.015 – 0.048 (0.0006 – 0.0019) 0.098 (0.0039) EX 0.050 – 0.083 (0.0020 – 0.0033) 0.120 (0.0047) Valve Spring Free Length 21.77 (0.8570) 21.00 (0.8268) Cam Pulley Cam height 22.46 (0.884) 22.16 (0.8724) Cam pulley I.D. 4.020 – 4.070 (0.1583 – 0.1602) 4.100 (0.1614) Cam pulley shaft O.D. 3.990 – 4.000 (0.1571 – 0.1575) 3.950 (0.1555) Cylinder Barrel Barrel I.D. (cam pulley bearing) 4.000 – 4.018 (0.1575 – 0.1582) 4.050 (0.1594) Carburetor Main jet #37 Spark Plug Gap 0.6 – 0.7 (0.024 – 0.028) Ignition Coil Resistance Primary coil 0.75 – 0.92 Ω Secondary coil 6.1 – 9.3 kΩ Air gap (at flywheel) 0.2 – 0.4 (0.008 – 0.016) 400-6330 Zéphirin-Paquet St. Québec QC G2C 0M3 Canada © ConsuLab Educatech Inc, 2026. All rights reserved. Student Assignments Instructor Notes and Answer Keys About This Manual SA-1 - Level I — Engine Familiarization and Component Identification Instructor Notes Answers SA-2 - Level I — Engine Teardown and Component Relationships Instructor Notes Answers SA-3 - Level II — Understanding Engine Timing Instructor Notes Answers SA-4 - Level II — Ignition Coil Positioning and Adjustment Instructor Notes Answers SA-5 - Level II — Valve Clearance Adjustment Instructor Notes Answers SA-6 - Level I — Spark Plug Adjustment Instructor Notes Answers SA-7 - Level III — Piston Ring End Gap Adjustment Instructor Notes Answers SA-8 Level I Engine Reassembly Instructor Notes Answers Engine Fundamentals Assessment Glossary Glossary Manufacturer Specifications Torque Specifications Honda GX35 Specifications
