Small Engine Repair
Small Engine Repair
ACTIVITY GUIDE For a Briggs & Stratton Model 12H302 Four-Stroke Engine Quantum 120000 Series)
Developed by: Andrew Jones Jones – – GMCS
Tim Thornton - UNBF
Chris Brown – Brown – CNHS
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TABLE OF CONTENTS
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TABLE OF CONTENTS
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Overview:
Objectives
Required Items
In this module the student will:
Identify the theory, uses and operation of small gas engines.
Explore engine operation using the four-stroke and two-stroke cycle principles.
Develop knowledge of proper and safe tool usage.
Interact with with the mechanical, electrical and fuel systems of a small gas engine.
Complete the disassembly and reassembly of a small gas engine.
All of the required tools and equipment equipment you will will need to complete this module are available from your teacher. Tools Module book Computer/Internet Access Book: Care & Repair (By Briggs & Stratton) Digital Camera
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Activity 1: Tools Check List
Assignment 1: Find the Toolbox, and do an inventory using the handout sheet. When you have completed the inventory, call your instructor over and show him/her where each item is located. He may quiz you on where they may be used.
Socket Set
Most of the loosening of bolts on the engine will be done with sockets. (see illustration on next page)
All Metric & SAE sockets sockets Spark Plug Socket Ratchet Socket Extensions Flywheel Nut Socket Wrenches
A Set of Wrenchs – A wrench can sometimes reach places that can’t be reached by a socket.
Metric Wrenche W renches s Imperial Wrenche W renches s Hammer You may need to loosen a part (like the flywheel). Only use a RUBBER hammer to hit an engine part.
A soft rubber rubber hammer Safety Glasses
There are some steps (such as removing the valve springs that require safety glasses). SAFETY FIRST!
Safety glasses 4 A Jones - GMCS GMCS
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0 - 3” micrometers
- This tool is used to Micrometer measure engine parts that are can be affected by wear (such as the cylinder bore or piston) This is used when the greatest precision is required down to 1/10,000 of an inch.
Micrometer Size Range: _______
Telescoping Gauge – Gauge – Up Up to 3”
Telescoping gauges are used along with the micrometer to measure the diameter of the cylinder. (Use the gauges and then measure the gauge with the micrometer)
Set of 5 Feeler Gauges - Up to 0.35
Feeler Gauges are for measuring the gap in the spark plug and distance between the magneto and the flywheel. They measure very small spaces precisely.
Set Valve spring compressor
This tool compresses the valve springs so the valves can be removed.
Spring Compressor
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Piston Ring Compressor
This tool compresses or squeezes the rings on the piston so the piston tapped back into the cylinder.
Piston Ring Compressor
Gear Puller The flywheel is fitted on a tapered shaft and that tapper makes it difficult to remove the shaft even when the nut is removed. This tool helps pull the flywheel off the shaft.
Gear Puller Torque Wrench
It looks similar to the ratchet in a socket set. It is used for bolts that have to tightened with a specific amount of force.
Torque Wrench
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Socket Set
Dee Sockets Reducers Socket Extension
1/2” Ratchet
3/8” Ratchet
15/16” Fl wheel Nut
13/16” S ark Plu Socket
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Activity 2: Small Gas Engines Although the first internal combustion engine was invented in 1680 (by a Dutchmen), it was the 1900s before they became inexpensive enough to become widespread. An internal combustion engine uses the energy from an explosion (of gasoline and air) in the cylinder to turn a shaft (that power a mower blade, or, wheels). An engine changes chemical energy (the fuel explosion), into mechanical energy (the turning of the shaft). Many improvements have made engines lighter, cheaper, more efficient, and more environmentally friendly.
Source: http://www.themotorreport.com.au/6915/the-realmccoey-on-ron-research-octane-number
Assignment 2: Engine Developments Use the book: S mall E ng ine Care and R epair to answer these questions. 1. Starting in 1920, Briggs and Stratton became one of the most innovative engine designers. We should get an idea how much they contributed to the development of engines. (see page 7 of the book) a. Which Model of engine did Briggs & Stratton first invent for lawn mowers and other small applications back in the 1920s? b. What big development occurred at Briggs & Stratton in 1953 that made engines lighter and easier to use? 2. There is a gas powered clothes machine machine on p. 7. Why would anyone have bought one of these in the early 1900’s ?
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Activity 3: Safety
General Safety Considerations
We have less safety precaustions than normal because:
We will not be starting the engine.
We have removed the gasoline & oil/lubricants from the engine to protect you and your clothes
Safety instructions
Wear safety glasses when removing and inserting the value springs.
Use the tools in the way they were designed to be used.
Don’t fool around If you were going to work on an engine at home, it’s important that you know the proper safety rules to keep you safe
.
Assignment 3: List the 11 “Safe Maintenance” points and 7 “Protecting Your Health” points on page 13 of S mall E ng ine Care & Maintenance.
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Activity 4: Preparing for Disassembly You will be removing 20 components off the engine in the next activity. Each component has bolts or small parts that can’t be lost.
Assignment 4: Construct a storage method with 20 compartments. (Probably 2 of these like in the picture) The sections should be constructed so small pieces can’t slide into another section. (boxes will be in the Garbage bin or check with the custodian)
Purpose: Put the pieces in your storage compartment in the order of disassembly. Re-assemble the engine by taking pieces out in the reverse order.
Show this system to the instructor before going on .
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Activity 5: Disassembly Have your instructor assign you an engine that you can start to disassemble.
Step 1
Remove Spark Plug & Fuel Tank Spark Plug Wire: This wire connects the coil to the spark plug.
Never touch it while the engine is running, you might get a shock). Removing the spark plug wire can be accomplished by pulling the cap straight up off the spark plug. DO NOT PULL THE WIRE . Use a socket wrench to remove the spark plug.
2
Fuel Tank: Remove 3 bolts that attaches the fuel tank to the block. . (7/32 socket)
3
Oil Dip Stick: There is one screw holding the dip stick. Then, pull up on it to remove it from the hole. Put this screw with the other ones from the gas tank.
Disconnect one end of the Fuel hose from the fuel tank. Use pliers to squeeze the hose clamp and slide it up the hose. Then, twist the hose side to side while pulling from the tank. Now the tank should lift off easily.
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Step 4
Remove Air Filter The Breather: This filters the air going in the carburetor. Dirty air will plug up the carburetor.
Remove the top cover of air breather filter by removing one screw and folding the cover down.
5
Air Filter : Remove air filter
6
Air Breather Assembly: Remove lower breather assembly (3 screws).
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Step 7
Remove Carburetor The Carburetor: The carburetor mixes the fuel with the air.
Remove 2 bolts attaching the carburetor to the engine. (3/8 socket) You can leave the fuel line attached if you wish.
Note: On the top of the carburetor, there are a couple of springs. You need to note their position before removing the carberator. One goes to the choke and other one is the governor spring. Draw a sketch that will remind you where these are located .
Step
Remove Starter Assembly
8
Starter Assembly: Better known as the pull chord, this manually rotates the engines until it starts .
Remove 4 bolts securing starter assembly to the engine and remove starter assembly. (3/8 socket)
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Coil / Ignition Armature: The coil creates the electrical energy that creates the spark in the sparkplug.
Unhook the wire from back of coil and remove the coil. (7/32 socket)
10
The Engine Break : It shuts off the engine when the safety handle is released. (For example, when you start a lawn mower, you have to hold a handle down or else the mower will stop). (5/16 socket)
Remove the engine brake by removing two screws.
This may not be present! 11
Flywheel: The flywheel cools the engine as it spins around.
Remove 1 bolt holding the flywheel using a 15/16 socket.
Key
Continued…
Tap the shaft/fly wheel with a rubber hammer or use the gear puller tool.
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Small Engine Repair CAUTION: There is a “key” (a tiny rectangular piece of metal) that is between the shaft and the flywheel. Do Not Lose This (Tape it right to your storage box)
Step 12
Key
Action: Remove the Muffler & Breather Muffler : A muffler reduces the noise of the engine. (7/16 socket)
Remove the muffler by using a socket wrench. There are 2 bolts to remove on the muffler .
13
Crank Case Breather: This allows air into the crankcase.
Remove the two screws holding the crank case breather
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Step 14
Action: Remove Cylinder Head Cylinder Head: A. The bolts have to be removed so they can be put back in the same hole.
Make a template of the cylinder head out of cardboard. B. Loosen each bolt and place each bolt securely in the hole of the template as you remove it. C. Remove cylinder head D. Leave the gasket in place, or if it is loose, put it somewhere so that it doesn’t get damaged.
E. The Gasket : This creates a seal that creates a tight compartment for combustion. If the seal is broken, the engine loses compression and it will not run. Usually, you have to replace the gaskets each time you take an engine apart (unless your careful not to rip it)
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Step 15
Action: Remove Timing Cover Timing Cover: Remove 7 bolts holding the timing cover. (3/8 socket)
Remove timing cover (it might need a tap from a soft hammer)
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The Governor Mechanism: The governor mechanism is the first thing to be removed. It is fitted over top of the camshaft.
This mechanism regulates the engine speed through the governor arm that is connected to the throttle. Also, it is used to splash the oil for lubricating the engine parts
Governor Arm
17
Cam Shaft: Pull out the cam shaft using your fingers
Note: the two (2) lifters will drop out
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Step 18
Action: Remove Piston Connecting Rod: Remove two connecting rod bolts.
Remove connecting rod cap. It may need a slight tap with the handle of a hammer.
Take note of the way the piston is positioned The Piston: The Piston moves up and down to compress the gases in order to create combustion. The rings around the outside keep gases from passing by the piston causing the engine to lose compression.
Push the piston UP through the cylinder and remove from the engine. It will be stiff moving it.
Step Action: Remove Crankshaft 19
Crank Shaft: The crankshaft is rotated by the movement of the piston. The energy is transferred to the wheels and/or the blade of the lawnmower.
Remove the crank shaft by pulling it straight out.
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Step
Action: Remove Valves & Springs
Use Safety Glasses for this step.
Remove the Breather Cover that covers the value springs. Using the valve spring compressor, compress the valve spring and remove from engine as shown
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below.
20
Students find this the most difficult step. Be patient. Value Springs: The valve springs keep the values in the closed position.
With spring compressed, push valve down slightly and you will have to push the compressed spring sideways to release the valve from the lock. Take a look at illustrations below for extra assistance. Slide the bottom of the spring compressor tool between the bottom of the value spring and the stopper. Then tighten the handle on the top of the tool. The tool will start to force the spring up. When the spring is half compressed, you can slide the stopper of the end of the value. Now the value will slide out once the tool is released.
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Assignment 5: Get a digital camera from the instructor. Create a PowerPoint made up these 6 components: 1. Title Page: Small Gas Engines (and a picture of the engine) On each page include a name, a picture and an explanation of each part that makes up the system. (Ask how to make a textbox) 2. The Ignition System: (Pull Chord, Spark Plug, Coil, Flywheel) 3. Fuel System: (Fuel Tank, Fuel Line, Carburetor, Valves, Air Filter, Primer Bulb, Muffler) – This will take 2 slides (don’t crowd it) 4. Cooling System (Flywheel) 5. Compression System (Piston, Engine Block, Gaskets, Rings – ask about the rings) 6. Mechanical System – (Crankshaft, Camshaft, Governor, Throttle, Engine Brake)
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Assignment 6: Micrometer Lab In this lab, you will learn how to measure precisely. Why do we need this? Engines have very little tolerance and just slight wear can cause gaps that lose compression in the engine. We have to measure to the 1/10,000 of an inch. You will:
Learn to read a micrometer from the PowerPoint tutorial Measure using Telescoping gauges and a Micrometer. Record your answers to the 4th decimal place on the worksheet.
View the PowerPoint presentation on learning how to read a micrometer.
We have two tools to measure precise distances down to 1:10,000 of an inch. The micrometer is the most accurate. Next we have a digital caliper. Find these two tools in your toolbox.
Caliper
Micrometer
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Step Action: Measure the Cylinder 1
Using telescoping gauge and the proper sized Micrometer or Caliper (only if you don’t have a micrometer that fits). Measure the inside diameter of the cylinder. Measure every inch (25mm) down the cylinder and again at 90° Record your meaurements on your own paper : 1. _____________ 2. _____________ 3. _____________ 4. _____________
2
Rotate the micrometer 90° and measure again every inch down the cylinder. Record your meaurements on your own paper : 5. _____________
90°
6. _____________ 7, _____________ 8. ___________
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Step
3
Action: Measure Piston Measure the piston skirt 9. ___________
Step 4
Action: Measure Valve Stem Measure valve stems for wear 10. ___________ 11. ___________
5
Measure the three journals on the crankshaft. 1.
Connecting Rod Journal - 12 . ___________
2.
Flywheel Journal - 13 . ___________
3.
PTO Journal - 14. ___________
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Assignment 7: Reassemble the engine using the following directions. 1
2
Normally, we would lubricate cylinder and valve stems with white grease, but we won’t be doing this today. Valve Springs: Insert the valves (if they are too long, then you put the wrong one in the wrong hole).
Put the spring on the end of the value rod. Use the compression tool to compress the spring about half way. Then, drop the stopper on the end of the valve shaft. Don’t forget your safety glasses.
3
Crankshaft: Insert the crankshaft (Make sure it is in the right direction)
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