Micro EngineRepair Manual

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BRIGGS & STRATTON SMALL ENGINES TEXTBOOK PART #CE8020

A comprehensive hard cover textbook titled SmallEngines was recently published by American TechnicalPublication of Homewood, Illinois. The text wasauthored by R. Bruce Radcliff, Former CustomerEducation Director for Briggs & Stratton. This entirelynew book is authorized by Briggs & Stratton, theworlds largest manufacturer of small air cooledengines.

In addition to covering all aspects of small enginetheory, the subjects of shop safety, tools,troubleshooting and engine emissions are featured.

The book contains 12 chapters covering the basicprinciples of small engine operation and servicethrough engine theory to electricity and failure analysis.The book goes far beyond the procedures in the repairmanual to present the Why in engine design featuresand operation fundamentals.

Included are current high priority topics such as engineoil, reformulated fuels, engine emissions as well as thelatest information on engine application.

Fully illustrated, using computer generated line art andphotographs, each topic is covered in easy tounderstand terms and four color illustrations.

This should be a standard reference book for all smallengine repair facilities, vocational schools andconsumers.

Small Engines is available through any Briggs &Stratton source of supply.

BRIGGS & STRATTON SMALL ENGINE CARE &REPAIR BOOK PART #274041

For the novice a step-by-step guide to small enginecare and repair.The full color book is 128 pages and includes over 300color photos and easy-to-follow instructions. Conceptsare introduced that apply to virtually every small enginemaking this appealing to a very broad audience. It offersconsumers a step-by-step guide for saving moneythrough preventive maintenance and do-it-yourselfrepair. Includes a troubleshooting section to easilydiagnose common small engine problems. Featuresintroductory projects that require no prior knowledge, aswell as advanced projects for the experienced repairperson. It utilizes the Briggs & Stratton name which isrecognized worldwide as the small engine leader.

GENERAL INFORMATION Section 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DISASSEMBLY AND REPAIR Section 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

COMPONENT LOCATION Section 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TABLE OF CONTENTS

I

II

English to Metric Conversion Table

Fraction Decimal mm Fraction Decimal mm1/64 0.0156 0.3969 33/64 0.5156 13.0969

1/32 0.0312 0.7938 17/32 0.5312 13.4938

3/64 0.0469 1.1906 35/64 05469 13.8906

1/16 0.0625 1.5875 9/16 0.5625 14.2875

5/64 0.0781 1.9844 37/64 0.5781 14.6844

3/32 0.0938 2.3812 19/32 0.5938 15.0812

7/64 0.1094 2.7781 39/64 0.6094 15.4781

1/8 0.1250 3.1750 5/8 0.6250 15.8750

9/64 0.1406 3.5719 41/64 0.6406 16.2719

5/32 0.1562 3.9688 21/32 0.6562 16.6688

11/64 0.1719 4.3656 43/64 0.6719 17.0656

3/16 0.1875 4.7625 11/16 0.6875 17.4625

13/64 0.2031 5.1594 45/64 0.7031 17.8594

7/32 0.2188 5.5562 23/32 0.7188 18.2562

15/64 0.2344 5.9531 47/64 0.7344 18.6531

1/4 0.2500 6.3500 3/4 0.7500 19.0500

17/64 0.2656 6.7469 49/64 0.7656 19.4469

9/32 0.2812 7.1438 25/32 0.7812 19.8438

19/64 0.2969 7.5406 51/64 0.7969 20.2406

5/16 0.3125 7.9375 13/16 0.8125 20.6375

21/64 0.3281 8.3344 53/64 0.8281 21.0344

11/32 0.3438 8.7312 27/32 0.8438 21.4312

23/64 0.3594 9.1281 55/64 0.8594 21.8281

3/8 0.3750 9.5250 7/8 0.8750 22.2250

25/64 0.3906 9.9219 57/64 0.8906 22.6219

13/32 0.4062 10.3188 29/32 0.9062 23.0188

27/64 0.4219 10.7156 59/64 0.9219 23.4156

7/16 0.4375 11.1125 15/16 0.9375 23.8125

29/64 0.4531 11.5094 61/64 0.9531 24.2094

15/32 0.4688 11.9062 31/32 0.9688 24.6062

31/64 0.4844 12.3031 63/64 0.9844 25.0031

1/2 0.5000 12.7000 1 1.0000 25.4000

III

Drill Size Decimal Equivalent In Inches

60 .040

59 .041

58 .042

57 .043

56 .0465

55 .052

54 .055

53 .0595

1/16 .0625

52 .0635

51 .067

50 .070

49 .073

48 .076

5/64 .0781

47 .0785

46 .081

45 .082

44 .086

43 .089

42 .0935

3/32 .0938

41 .096

40 .098

39 .0995

38 .1015

37 .104

36 .1065

7/64 .1094

35 .110

34 .111

33 .113

32 .116

31 .120

1/8 .125

30 .1285

29 .136

28 .1405

9/64 .1406

27 .144

26 .147

25 .1495

24 .152

23 .154

5/32 .1562

22 .157

21 .159

20 .161

19 .166

18 .1695

11/64 .1719

17 .173

16 .177

15 .180

14 .182

13 .185

3/16 .1875

12 .189

11 .191

10 .1935

9 .196

8 .199

7 .201

13/64 .2031

6 .204

5 .2055

4 .209

3 .213

7/32 .2188

2 .221

1 .228

A .234

15/64 .2344

B .238

C .242

D .246

E, 1/4 .250

F .257

G .261

17/64 .2656

H .266

I .272

J .277

K .281

9/32 .2812

L .290

M .295

19/64 .2969

N .302

5/16 .3125

O .316

P .323

21/64 .3281

Q .332

R .339

11/32 .3438

S .348

T .358

23/64 .3594

U .368

3/8 .375

V .377

W .386

25/64 .3906

X .397

Y .404

13/32 .4062

Z .413

27/64 .4219

7/16 .4375

29/64 .4531

15/32 .4688

31/64 .4844

1/2 .500

11

SECTION 1General Information

SECTION INDEX

PAGE

Safety 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Check-Up 6-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Compression 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Carburetion 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ignition 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Engine OperationEquipment Affecting 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hard Starting 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kick-Back 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Power Loss 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Will not Start 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vibration 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fuel Recommendations 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MaintenanceAir Cleaner 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Oil, LubricationCheck Oil Level 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Change Oil 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oil Capacity 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cooling System 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Oil Recommendations 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Spark Plug 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Engine Identification 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Tune-Up Procedure 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 2

In the Interest of Safety

This safety alert symbol indicates that thismessage involves personal safety. Thewords danger, warning and cautionindicate degree of hazard. Death, personalinjury and/or property damage may occurunless instructions are followed carefully.

You are not ready to operate this engine ifyou have not read and understood thefollowing safety items. Read the entireowners manual and the operatinginstructions of the equipment this enginepowers.

The Briggs & Stratton engine is made of the finest material in a state-of-the-art manufacturing facility. Please understand that Briggs& Stratton sells engines to original equipment manufacturers. It also sells to others in the distribution chain who may sell to theultimate consumer, an equipment manufacturer, another distributor or a dealer. As a result, Briggs & Stratton does not necessarilyknow the application on which the engine will be placed. For that reason, carefully read and understand the operating instructions ofthe equipment before you repair or operate it.You should also understand that there are equipment applications for which Briggs & Stratton does not approve the use of its en-gines. Briggs & Stratton engines are not to be used on vehicles with less than 4 wheels. They include motor bikes, aircraft productsand All Terrain Vehicles. Moreover, Briggs & Stratton does not approve of its engines being used in competitive events. FOR THATREASON, BRIGGS & STRATTON ENGINES ARE NOT AUTHORIZED FOR ANY OF THESE APPLICATIONS. Failure to followthis warning could result in death, serious injury (including paralysis) or property damage.

DO NOT run engine in an enclosed area.(Exhaust gases contain carbon monoxide,an odorless and deadly poison.)DO NOT remove fuel tank cap nor fill fueltank while engine is hot or running. (Allowengine to cool 2 minutes before refueling.)

DO NOT place hands or feet near moving or rotatingparts.DO NOT store, spill, or use gasoline near an openflame, nor near an appliance like a stove, furnace, orwater heater that uses a pilot light or can create aspark.DO NOT refuel indoors or in an unventilated area.DO NOT operate or tip engine/equipment at such a se-vere angle that causes gasoline spillage.DO NOT operate engine if gasoline is spilled or whensmell of gasoline is present or other explosive condi-tions exist. (Move equipment away from spill and avoidany ignition until gasoline has evaporated.)DO NOT transport engine with fuel in tank or fuel shut-off valve open.DO NOT choke carburetor to stop engine, especially inan enclosed vehicle. (Whenever possible, graduallyreduce engine speed before stopping.)DO NOT tamper with governor springs, links or otherparts to increase engine speed. (Run engine at speedset for equipment manufacturer.)DO NOT check for spark with spark plug removed.(Use an approved tester.)

DO NOT run engine without blower housing or othersafety shields removed when doing repairs.DO NOT crank engine with spark plug removed. (If en-gine is flooded, place throttle in FAST and crank untilengine starts.)DO NOT strike flywheel with a hammer or hard object asthis may cause flywheel to shatter in operation. (To re-move flywheel, use Briggs & Stratton approved tools andprocedures only.)DO NOT operate engine without a muffler. (Inspect peri-odically and replace if worn or leaking. If engine isequipped with muffler deflector, inspect periodically andreplace if necessary. Replacement parts must be sameas on original equipment.)DO NOT operate engine with an accumulation ofgrass, leaves or other combustible material in mufflerarea.DO NOT use this engine on any forest covered, brushcovered, or grass covered unimproved land unless aspark arrester is installed on muffler. The spark arrest-er must be maintained in working order by the ownerand/or operator. In the State of California the above isrequired by law (Section 4442 of the California PublicResources Code). Other states may have similar laws.Federal laws apply on federal lands.DO NOT touch hot muffler, cylinder, or fins which cancause burns.DO NOT start engine with air cleaner or air cleaner coverremoved.

Prior to work, read and understand the section(s) of this manual that pertain to the job. Follow all safety warnings.PULL starter cord slowly until resistance is felt. Then pull cord rapidly to avoid kickback and prevent hand or arm injury.WEAR suitable eye protection (safety glasses, goggles or face shield) when performing repair procedures. PREVENT ACCIDENTAL STARTING by removing spark

plug wire from spark plug when servicing engine or equip-ment. Disconnect negative wire from battery terminal ifequipped with electric starting system.

REMOVE blower housing periodically and clean engine.Keep cylinder fins and governor parts free of dirt, grassand other debris which can affect engine speed.

USE fresh gasoline. Stale fuel can gum carburetor andcause leakage.

CHECK fuel lines and fittings frequently for cracks orleaks. Replace if necessary.

USE ONLY Genuine Briggs & Stratton Parts or theirequivalent. The use of replacement parts which are not ofequivalent quality may damage the engine.

The engine exhaust from this productcontains chemicals known to the State

of California to cause cancer, birthdefects, or other reproductive harm.

13

Fuel and Oil Recommendations

FUEL RECOMMENDATIONS

GasolineThese engines are certified to operate on unleadedgasoline. Use clean, fresh, regular unleaded gasolinewith a minimum of 85 octane. Do not mix oil withgasoline. Fresh fuel prevents gum from forming in fuelsystem or on essential carburetor parts. Purchase fuelin quantity that can be used within 30 days to assurefuel freshness. We recommend the use of Briggs &Stratton Gasoline Additive. (See your AuthorizedBriggs & Stratton Service Dealer for Part No. 5041 orthe single-use pouch.)

In countries other than U.S.A., leaded gasoline may beused if it is commercially available and unleaded isunavailable.

NOTE: Some fuels, called oxygenated or reformu-lated gasolines, are gasoline blended withalcohols or ethers. Excessive amounts ofthese blends can damage the fuel systemor cause performance problems. Do notuse gasoline containing Methanol. If anyundesirable operating symptoms occur,use gasoline with a lower percentage ofalcohol or ether.

LUBRICATION

Engine Oil

C -30STARTING TEMPERATURE RANGE ANTICIPATED BEFORE NEXT OIL

CHANGE

F -20 0 20 40 60 80 100-20 -10 0 10 20 30 40

**

32

SAE VISCOSITY GRADES

* Air cooled engines run hotter than automotiveengines. Use of non-synthetic multi-viscosity oils(10W-30, etc.) in ambient temperatures above40F (4C) will result in high oil consumption. Ifmulti-viscosity oil is used, check oil level morefrequently to prevent engine damage due to lackof lubrication.

** SAE 30 oil, if used below 40F (4C), will result inhard starting and possible engine damage due toinadequate lubrication.

Note: Synthetic oil meeting ILSACGF-2, API certification mark and APIservice symbol (shown at left) with SJ/CF ENERGY CONSERVING or high-er, is an acceptable oil at all temperatu-res. Use of synthetic oil does not al-ter required oil change intervals.

CHANGE OIL after first 5 hours of operation. Thereafter, change oil monthly or every 50 hours of operation. Changeoil more often if engine is operated under heavy load or in high ambient air temperatures.

During normal operation, partially burned gasoline, small particles of metal from the cylinder walls, pistons, bearings,combustion deposits, and dust particles from the air will gradually contaminate the oil. If oil is not changed regularly,these foreign particles can cause increased friction and a grinding action which shortens the life of the engine. Fresh oilalso assists in cooling. Old oil gradually becomes thick and loses its cooling ability as well as its lubricating qualities.

Check Oil LevelPlace the warm engine with the dipstick facing up.

Use a support (2), Fig. 1, to level the engine.

NOTE: The engine MUST be level to obtain anaccurate oil level measurement.

Unscrew the dipstick (1), Fig. 1, and wipe it with a rag.

Replace the dipstick, thread the dipstick in completely.

Unscrew the dipstick to check the oil.

Fig. 1

1 4

BE SURE OIL LEVEL IS PROPERLY MAINTAINED.Always fill to dipstick FULL mark (2), Fig. 2.

Fig. 2

Change Crankcase OilRemove dipstick, Fig. 1.

Invert the engine to drain oil while the engine is warm.

Fill engine with 2.7 oz. (80 ml.) of new oil.

Replace dipstick.

Cooling SystemGrass particles, chaff or dirt can clog the air cooling system. Continued operation with a clogged cooling system cancause severe overheating and possible engine damage. This should be a regular maintenance operation, performedyearly. Clean more often if necessary.

Air CleanerA properly serviced air cleaner protects internal partsof the engine from dust particles in the air. If air cleanermaintenance instructions are not carefully followed,dirt and dust that should be collected in the air cleanerfoam element will be drawn into the engine.

Remove the air cleaner cover (2) and examine thefoam air cleaner element (1) whenever the engine isserviced Fig. 3. Wash the element if it is dirty. Replacethe foam element if it shows signs of damage.

Fig. 3

Breather Check ValveWith the air cleaner removed inspect the breathercheck valve (3), Fig. 4. Remove any obstructions fromthe check valve. The check valve should be flexibleand remain closed as shown.

Fig. 4

15

Spark PlugReplace spark plugs if electrodes show signs of wear,or the porcelain is cracked. Set spark plug gap at .022 .028 Inch (.56 .71 mm) as shown, Fig. 5. Torquespark plugs to 20 Nm (180 in. lbs.).Briggs & Stratton recommends spark plug number696876 for the Micro Engine.

Fig. 5

Tune-Up Procedure Performing these steps will either assure that the engine is functioning properly or will point out necessary repairs.

Step No.

1. Remove spark plug lead from spark plug.

2. Remove air cleaner.

3. Check oil level and drain. (Clean fuel tank and lines. Replace in-tank fuel filter.)

4. Remove blower housing, inspect rope and rewind assembly.

5. Clean cooling fins and entire engine.

6. Check compression and do a cylinder leakdown test.

7. Remove carburetor, disassemble and inspect for wear or damage. Wash in solvent, replace parts asnecessary and assemble.

8. Check armature, inspect all wires for breaks or damaged insulation. Be sure lead wires do not touchflywheel. Check stop switch and lead.

9. Remove flywheel, check for oil seal leakage, both flywheel and PTO sides. Check flywheel key.

10. Install flywheel. Time engine if necessary. Set air gap. Check for spark with #19368 tester.

11. Remove spark plug. Remove cylinder head, check gasket and clean carbon. Inspect valves for properseating.

12. Replace cylinder head. Torque to specifications, set spark plug gap or replace plug if necessary.

13. Replace oil and fuel, check muffler for restrictions or damage.

14. Adjust remote control linkage and cable (if used), for correct operation.

15. Service air cleaner and breather check valve. Check gaskets and element for damage.

16. Run and adjust idle speed.

1 6

Check-UpMost complaints concerning engine operation can beclassified as one or a combination of the following:1. Will not start2. Hard starting3. Kicks back when starting4. Lack of power5. Vibration6. Erratic operation7. Overheating8. High oil consumptionWhen the cause of malfunction is not readily apparent,perform a check of the compression, ignition andcarburetion systems. This check-up, performed in asystematic manner, can usually be done in a matter ofminutes. It is the quickest and surest method ofdetermining the cause of failure and averting futureproblems. The basic check-up procedure is the samefor all engine models, while any variation, by model,will be shown under the subject heading.

NOTE: What appears to be an engine malfunc-tion may be a fault of the poweredequipment rather than the engine. Ifequipment is suspect, see Equipment Affecting Engine Operation.

Check Compression

WARNING: Before checking compression, re-move spark plug wire from spark plug andground to engine.

A leakdown test is the only accurate method ofchecking the sealing ability of the combustion cham-ber. This test uses compressed air and a leakdown testtool.

If compression is poor, look for:

1. Loose cylinder head bolts

2. Blown head gasket

3. Burned valves, valve seats

4. Insufficient tappet clearance

5. Warped cylinder head

6. Warped valve stems

7. Worn bore and/or rings

8. Broken connecting rod

Check Ignition

WARNING: Do not remove spark plug whenchecking ignition.

Connect spark plug wire to long terminal of tester, Tool#19368 and ground tester to engine with alligator clip.Operate starter and observe spark gap in tester. Ifspark jumps tester gap, you can assume ignition isgood. Try a new spark plug.

If spark does not occur, look for:1. Improperly operating interlock system (when

equipped)2. Shorted ground wire (when equipped)3. Shorted stop switch (when equipped)4. Armature failure5. Worn bearings and/or shaft on flywheel side only

NOTE: If engine runs but misses during opera-tion, a quick check to determine if ignitionis at fault can be made by inserting the#19368 tester between the ignition cableand the spark plug. A spark miss will bereadily apparent.

Check CarburetionBefore making a carburetion check, be sure the fueltank has an ample supply of fresh, clean gasoline.Inspect the mixture needles per specification. Check tosee that the choke closes completely. If engine will notstart, remove and inspect the spark plug.

If plug is wet, look for:

1. Over choking

2. Excessively rich fuel mixture

3. Water in fuel

If plug is dry, look for:

1. Leaking carburetor mounting gaskets

2. Inoperative pump.

3. Plugged fuel line or filter.

A simple check to determine if the fuel is getting to thecombustion chamber through the carburetor is toremove the spark plug and pour a small quantity ofgasoline (1 teaspoon or 10 ml.) through the sparkplug hole. Install spark plug. If the engine fires a fewtimes and then quits, look for the same condition asfor a dry plug.

17

Check-Up contd

Equipment-Affecting Engine OperationFrequently, what appears to be a problem with engine operation, such as hard starting, vibration, etc., can be causedby the equipment being powered rather than the engine itself. Since many varied types of equipment are powered byBriggs & Stratton engines, it is not possible to list all of the various conditions that may exist. Listed are the mostcommon effects of equipment problems, and what to look for as the most common cause.

Hard Starting, Kickback, or Will Not Start1. Loose blade blade must be tight to shaft or adaptor. Check for partially sheared flywheel key, or damaged blade

and hub.

2. Starting under load see if the unit is not engaged when engine is started; if the unit is engaged, that it does nothave a heavy parasitic load.

3. Check choke or speed control assembly for proper adjustment.

4. Check interlock system for shorted wires, loose or corroded connections, or defective modules or switches.

Vibration1. Cutter blade bent or out of balance remove and balance. Check for partially sheared flywheel key.

2. Crankshaft bent replace.

3. Worn blade coupling replace if coupling allows blade to shift.

4. Mounting bolts loose tighten.

Power Loss1. Bind or drag in unit if possible, disengage engine and operate unit manually to check for any binding action.

Engine IdentificationGeneral Model Series numbers are stamped on theidentification plate (1) located on the bottom of yourengine. To get replacement parts or technical assistancenote your engine Model, Type, and Code.

Fig. 6

1 8

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1SECTION 2Disassembly and Repair

SECTION INDEX

PAGE

DisassemblyExternal Engine Components 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Short Block 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AssemblyShort Block 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Valve Clearance Check and Adjust 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . External Engine Components 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Carburetor RepairDisassembly 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assembly 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SpecificationsDimensions 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Torque Specifications 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NOTE: When removing screws from the engine, the screw threads will loosen aluminum particles which can getinto the engine:Clean thoroughly whenever removing screws from the engine.Do not use impact tools to remove or install screws.Use lubricant liberally whenever removing screws.

NOTE: There is no provision to bore or hone the engine block. If the piston bore is worn or damaged, replace theengine.

2Disassembly

2. Remove screws from the blower housing/rewind(1) and cylinder shield (2) covers. Remove covers,Fig. 1.

NOTE: Remove screws with the T-25 bit (6,Fig. 5) from Briggs & Stratton Tool #19442Torqux Star Bit Set.

3. Disconnect the fuel lines (3) from the carburetor.

NOTE: The fuel RETURN line is clear and goeson the plastic barbed fitting.The fuel SUPPLY line has a green dotnear one end and goes on the brassfitting.

4. Remove the dipstick (4). Drain the oil from thecrankcase.

Fig. 1

Rewind Starter

CAUTION: WEAR SAFETY glasses whileperforming any rewind starter repair.

1. Pull starter rope out and hold.

2. Inspect starter rope. Replace the rope if anystrands are frayed or broken.

Starter Rope1. Pull end of rope from handle Fig. 2. Untie or cut off

the knot at end of rope (1). While holding the pulley,slowly allow the rope to retract into the rewind, re-lieving return spring pressure.

2. If the starter rope was cut for removal, burn the cutend of the rope with an open flame. Using caution,wipe the end of the rope with a waste cloth while itis still hot, to prevent swelling and unravelling.

NOTE: If replacing the starter rope, check theparts list to be sure the correct diameterand rope length is used. The servicereplacement rope is cut to length asrequired.

Fig. 2

33. Insert rope through handle (1). Tie knot asshown, Fig. 3.

4. If re-using old rope, burn pulley end of rope with amatch.

5. Using caution, while rope is still hot, wipe withwaste cloth to prevent swelling and unraveling.

6. Pull knot into cavity in handle.

Fig. 3

Wind Spring1. Turn pulley clockwise (arrow) until spring is wound

tight.2. Rotate pulley counterclockwise until rope hole in

pulley is in line with starter housing eyelet (1) andhold pulley, Fig. 4.

Install Rope to Starter1. Insert unknotted end of rope through starter hous-

ing eyelet and rope hole in pulley.2. Tie a knot in the rope and pull tight. Pull knot into

the cavity of the pulley3. While holding starter rope handle, slowly let pulley

pull starter rope into starter.

Fig. 4

4External Engine Components

1. Remove the ignition armature (5), Fig. 5.

NOTE: Remove screws with the T-25 bit (6,Fig. 5) from Briggs & Stratton Tool #19442Torqux Star Bit Set.

Fig. 5

2. Install Briggs & Stratton Tool #19538 FlywheelPuller (9) with the concave side facing the flywheeland underneath the starter pawls (7) as shown,Fig. 6.

3. Insert the driver (8) to the flywheel nut as shown,Fig. 6.

4. Use Briggs & Stratton Tool #19433 Flywheel StrapWrench to secure the flywheel. Turn the drivercounterclockwise to remove the flywheel and fly-wheel nut from the crankshaft.

Fig. 6

55. Remove the top three muffler bolts (10), Fig. 7.Remove the muffler.

Fig. 7

6. Remove the air cleaner assembly.

7. Remove two nuts (11), Fig. 8. Slide carburetorfrom the studs.

Fig. 8

8. Remove seven cylinder head bolts (12), Fig. 9.Remove cylinder head.

Fig. 9

69. Remove two screws (13), Fig. 10. Remove thecarburetor spacer.

Fig. 10

Short Block

1. Remove two screws. Remove valve cover (1) andgasket, Fig. 11.

Fig. 11

2. Turn the valve retainers so the release holes faceout. Lift the front of the retainer (2) with a smallscrewdriver to release the retainer from the valve,Fig. 12.

Fig. 12

73. Remove the valves, springs and retainers.

NOTE: The intake valve has a valve oil seal on topof the valve spring, Fig. 13. The exhaust valve has an exhaust springcentering cap on top of the valve spring.

Fig. 13

4. Remove the crankcase cover bolts (3), and crank-case cover (4) with gasket, Fig. 14.

Fig. 14

85. Rotate the crankshaft until the piston pin is alignedwith the access hole in the cylinder.

6. Use a small screwdriver or similar tool in the re-cess of the piston (5) to remove the piston pin re-taining clip, Fig. 15. Discard the used retainingclip.

CAUTION: Wear eye protection when remov-ing piston pin retaining clip.

Fig. 15

7. Remove the piston pin by inserting a tool (6) intothe hole of the piston pin. Use a twisting motionand pull the pin out of the piston, Fig. 16.

NOTE: Do not apply downward pressure on thepiston pin. Use caution to avoid piston andbore damage.

Fig. 16

8. Rotate the crankshaft one revolution and positionthe crankshaft throw near bottom-dead-center(BDC), Fig. 17. This will leave the piston near thetop of the bore. Lift the connecting rod (7) off of thecrankpin, and remove the connecting rod.

Fig. 17

99. Push the piston (8) out of the cylinder (9), Fig. 18.

Fig. 18

10. Clean and inspect the cylinder. Measure the cylin-der bore twice, at right angles, at the top (10),middle (11) and bottom (12) of the piston ring trav-el, Fig. 19. Standard cylinder bore dimension is1.575 in. (40.0 mm). Discard the cylinder if thebore is 1.578 in. (40.08 mm) or over.

11. Remove the piston rings from the piston. Clean, in-spect and measure the piston.Standard piston diameter is 1.573 in. (39.95 mm).Piston-to-cylinder clearance is .001 .003 in. (.025 .076 mm).

12. Clean all carbon from the ends of the old pistonrings (16) and from the cylinder bore.

Fig. 19

13. Insert rings one at a time .5 in. (13 mm) into the cyl-inder.

14. Check the ring end gap with a feeler gauge (14),Fig. 20. Ring end gap (15) dimensions are:

Top Ring .004 .011 in. (.10 .28 mm)

2nd Ring .004 .011 in. (.10 .28 mm)

Oil Ring .008 .027 in. (.20 .69 mm)

If the piston ring end gap exceeds the largestdimension reject the piston ring.

Fig. 20

10

15. Remove two screws (17) and the camshaft cover,Fig. 21.

Fig. 21

16. Position the engine so that gravity keeps the tap-pets off of the camshaft, Fig. 22. Remove the cam-shaft (18).

Fig. 22

11

17. Remove the tappets (19) from the engine, Fig. 23.

Fig. 23

18. Support the cylinder with Tool # 19123 CylinderSupport Jack. Use Tool #19179 Driver to removethe ball bearing from the crankcase. Inspect theball bearing for wear, pitting or damage.

19. Press the crankshaft and bearing from the cylinderblock, Fig. 24. Inspect the crankshaft, cam drivegear and ball bearing. Replace the crankshaft ifany components are unserviceable.

20. Support the cylinder with Tool # 19123 CylinderSupport Jack. Use Tool #19450 Driver to press theball bearing into the crankcase.

Fig. 24

12

Assembly

Short Block

1. Clean all parts and gasket mating surfaces. In-spect all components for wear or damage, replac-ing as required.

2. Press the crankshaft into the cylinder block.

3. Lubricate the piston and cylinder. Compress thepiston rings as shown, Fig. 25.

4. Slide the piston into the cylinder with the 1 andC marks (7) on the side toward the piston pin ac-cess hole. Leave the piston near the top of the cyl-inder.

Fig. 25

5. Lubricate the connecting rod bearings.

6. Position the crankshaft near BDC.

7. Install the connecting rod with the dimple (8) to-ward the crankpin, facing the cover side of thecrankcase as shown, Fig. 26.

Fig. 26

13

8. Slide the piston down the cylinder bore and alignthe piston pin opening in the piston with the con-necting rod bearing.

9. Lubricate and install the piston pin (9), Fig. 27.

Fig. 27

10. Install a new piston pin retaining clip.

NOTE: DO NOT re-use the old clip. Always installa new piston pin retaining clip.

11. Install a new crankcase cover gasket. Install thecrankcase cover. Torque screws to 60 in. lbs. (7 Nm).

12. Install the tappets (10), Fig. 28.

13. Position the engine so that gravity keeps the tap-pets in place.

Fig. 28

14

14. Position the piston at top-dead-center (TDC),Fig. 29.

Fig. 29

15. Position the engine as shown, using gravity tokeep the tappets in position. Install the camshaftso the mark on the gear (12) is at the 12:00 oclockposition, between the lowest gear teeth of thecrankshaft, Fig. 30.

16. Install the camshaft cover and gasket. Torquecamshaft cover bolts to 50 in. lbs. (6 Nm).

Fig. 30

15

Valve Clearance Check and Adjust

1. Install the valves without the springs or retainers.

NOTE: The valve clearance must be checkedwhenever the camshaft cover has beenremoved.

2. Position the piston to 1/4 in. (6.35 mm) after TDCof the compression stroke. Both valves should beclosed. If both valves are not closed, rotate thecrankshaft 360 degrees (one revolution) into thesame position.

3. Hold the valve closed with finger pressure. Use afeeler gauge (1) to check the clearance betweenthe valve stem and tappet, Fig. 31. Clearanceshould be .002 .004 in. (.05 .10 mm). If thevalve clearance is less than specification, grind thetip of the valve stem until proper clearance is ob-tained.

NOTE: Use the correct fixture when grindingvalve stems to be certain the valve stem isground squarely.

Fig. 31

4. Install new intake valve oil seal (2) to the intakevalve spring, Fig. 32.

5. Install the valve spring centering cap to the ex-haust valve spring.

6. Install valve springs and retainers.

7. Install the valve cover. Torque the valve coverscrews to 60 in. lbs. (7 Nm).

Fig. 32

16

External Engine Components

1. Install new cylinder head gasket and cylinderhead.

2. Torque head bolts in sequence shown, Fig. 33.Torque to 75 in. lbs. (8.5 Nm).

3. Install carburetor spacer to studs. Torque to 60 in.lbs. (7 Nm).

4. Install new crankcase cover gasket and crankcasecover. Torque the cover screws to 60 in. lbs. (7Nm).

Fig. 33

5. Carefully install the flywheel. Make sure thekeyed part of the flywheel casting (8) is engagedto the keyway in the crankshaft, Fig. 34.

NOTE: The flywheel key is not serviceable, it ispart of the flywheel casting.

6. Install special flywheel nut. Torque to 170 in. lbs.(19 Nm).

7. Install the muffler. Torque to 40 in. lbs. (5 Nm).

Fig. 34

8. Install ignition armature. Use a feeler gauge to ad-just the air gap between the flywheel magnets andthe armature legs to .010 .014 in. (.25 .35 mm),Fig. 35. Torque armature screws to 60 in. lbs. (7Nm).

9. Fill engine with 2.7 oz. (80 ml.) of new oil. Install thedipstick.

10. Install the carburetor spacer, carburetor and aircleaner.

11. Connect the fuel lines to the carburetor.

NOTE: The fuel RETURN line is clear and goeson the plastic barbed fitting.The fuel SUPPLY line has a green dotnear the end and goes on the brass fitting.

Fig. 35

17

12. Replace the crankcase cover gasket. Install thecrankcase cover and screws. Torque the screws to60 in. lbs. (7 Nm) in the sequence shown, Fig. 36.

13. Install the blower housing and cylinder shield.Torque the screws to 40 in. lbs. (5 Nm).

Fig. 36

Carburetor Repair

Disassembly

1. Remove the carburetor from the engine.

2. Remove four screws (1), the primer bulb (2), andthe primer bulb cover (3), Fig. 37.

NOTE: The fuel RETURN line is clear and goeson the plastic barbed fitting (R).The fuel SUPPLY line has a green dotnear one end and goes on the inlet fitting(S).

Fig. 37

RS

18

3. Remove the primer backplate (4) and the dia-phragm (5), Fig. 38.

Fig. 38

4. Remove the fuel pump body (6) and diaphragm(7), Fig. 39.

Fig. 39

5. Remove the needle retaining screw (8), Fig. 40.

Fig. 40

19

6. Remove the needle (9), shaft (10), arm (12), andspring (11), Fig. 41.

Fig. 41

7. Remove the main jet (13) and O-ring from the car-buretor body, Fig. 42.

Fig. 42

20

8. Mark the idle speed screw side of the carburetorfor correct orientation during reassembly.

9. Remove two screws (15) and the throttle valve as-sembly (14), Fig. 43.

Fig. 43

10. Remove the throttle valve assembly (14) from thecarburetor body (15), Fig. 44. Clean and inspectall parts for wear or damage.

11. Blow out all passages with compressed air. Re-place parts as required.

Fig. 44

21

Assembly

1. Install the throttle valve assembly with the idlespeed adjustment screw lined up with the markmade during disassembly, Fig. 43.

2. Lubricate the O-ring (1) on the main jet. Install themain jet to the carburetor body, Fig. 45.

Fig. 45

3. Install the spring (3), gasket (4) and diaphragm (2),Fig. 46.

Fig. 46

22

4. Install the needle (5), arm (7), shaft (6) and spring(8). Make sure the slot in the needle remains in theyoke in the arm, and the spring remains straightunder the dimple in the arm, Fig. 47.

5. Install the shaft retaining screw.

Fig. 47

6. Replace the primer check valve (9), Fig. 48.

Fig. 48

7. Install the gasket (11) first, then install the dia-phragm (10), Fig. 49.

Fig. 49

11

23

8. Install the primer bulb (12) to the back plate (13),Fig. 50.

Fig. 50

9. Install the primer bulb cover (12), back plate (13),and fuel pump body (14) assembly to the carbure-tor body (15), Fig. 51.

10. Slide the carburetor onto the mounting studs andsecure with two nuts.

Fig. 51

24

SPECIFICATIONS

Micro Engine DimensionsMicro Engine Dimensions

Cylinder Bore 1.575 in. (40.00 mm)

Stroke 34cc Engine 1.066 in. (27.08 mm)

Stroke 40cc Engine 1.25 in. (31.75 mm)

Piston Diameter 1.573 in. (39.95 mm)

Piston-to-Cylinder Clearance .001 .003 in. (.03 .08 mm)

Piston Ring End Gap Top Ring .004 .011 in. (.10 .28 mm)

Piston Ring End Gap Second Ring .004 .011 in. (.10 .28 mm)

Piston Ring End Gap Oil Control Rings .008 .027 in. (.20 .69 mm)

Spark Plug Gap .022 .028 in. (.56 .71 mm)

Micro Engine Torque SpecificationsMicro Engine Torque Specifications

Bolt LocationQuantity

UsedTorque

Inch PoundsTorque

Newton Meters

Blower Housing 2 40 5

Camshaft Cover 2 50 6

Carb Adapter 2 60 7

Carb Mount Stud 2 24 3

Cylinder Head 7 75 8

Flywheel Nut/ Crank Adapter 1 170 19

Ignition Coil 2 60 7

Muffler Housing 2 40 5

Muffler 3 60 7

Rear Housing 4 24 3

Spark Plug #696876 1 180 20

Sump Cover 9 60 7

Valve Box Cover 2 60 7

31

SECTION 3Component Location

SECTION INDEX

PAGE

Component Location DrawingsCarburetor Components 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Crankshaft, Piston and Flywheel Components 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Camshaft and Crankshaft 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 2

Carburetor Components

1. Gasket2. Carburetor Screw (SS, 2 used)3. Carburetor Spacer4. Carburetor Spacer Screw (2 used)5. Gasket

6. Carburetor7. Nut (2 used)8. Air Cleaner Base9. Air Filter

10. Air Cleaner Cover

33

Crankshaft, Piston and Flywheel Components

1. Flywheel2. Crankshaft3. Connecting Rod4. Piston5. Oil Control Rings

6. Second Compression Ring7. Top Compression Ring8. Piston Pin Retaining Clip9. Piston Pin

10. Crankcase Cover

3 4

Camshaft, Crankshaft and Related Components

1. Valve Cover2. Valve Cover Gasket3. Camshaft4. Exhaust Valve5. Spark Plug6. Cylinder Head7. Intake Valve8. Intake Valve Seal9. Valve Spring (2 used)

10. Spring Retainer (2 used)11. Tappet (2 used)12. Crankshaft13. Gasket14. Camshaft Cover15. Breather Hose16. Breather17. Exhaust Valve Centering Cap

Copyright 2002 by Briggs & Stratton Corporation

All rights reserved. No part of this material may be reproduced ortransmitted, in any form or by any means, electronic or mechanical,including photocopying, recording or by any information storageand retrieval system, without permission in writing from Briggs &Stratton Corporation.

ACKNOWLEDGEMENTS

Customer Education:Director of Customer Education Dann Roark. . . . . . . . . . . Technical Writing Supervisor Donald Koloski. . . . . . . . . . . . . Technical Writing Trenton Technical Studio, Inc.. . . . . . . . . . . . . . . . . . . . . . .

Briggs & Stratton Graphic Services:Graphic Services Manager Debbie Pavletich. . . . . . . . . . . . . . . Pre-Press Supervisor Barb Peterson. . . . . . . . . . . . . . . . . . . Desktop Publisher Barb Peterson. . . . . . . . . . . . . . . . . . . . . . Graphic Designer Chad Goratowski. . . . . . . . . . . . . . . . . . . . . . .

For a complete list of all tools, order Briggs & Stratton Service Tools

Catalog, form number MS-8746.

PROFESSIONAL CD REPAIR MANUALSPART #CE3039This set of six CDs offers the user an opportunity tomaintain or repair a Briggs & Stratton engine withthe click of the mouse on their computer. The CDscover all Briggs & Stratton air cooled enginesproduced after 1981. The CDs allow you to view,print and troubleshoot.

NOTE: System Information for all CDs IBM PC or compatible This program operates only

on Microsoft Windows 95,NT, 98 Pentium, ME, XP"(or equal) 66 MHz processor or faster

16MB RAM or more 50MB of free hard drive space

8x (or faster) CD-ROM drive Video display capable of min.

16 bit color @ 800x600 res. 16-bit multimedia sound card Briggs & Stratton interactive

repair manuals will not runon 386 or earlier CPUs

BRIGGS & STRATTON CORPORATIONMilwaukee, WI 53201

Part No. 275072-7/02 Printed in U.S.A.www.briggsandstratton.com

Repair Manuals for otherBriggs & Stratton Engines, order:CE8069 Out of Production Engines (From 1919-1981)270962 Single Cylinder L Head (Built after 1981)271172 Twin Cylinder L Head272144 Vanguard V-Twin OHV 272147 Single Cylinder OHV273521 Intek V-Twin Cylinder OHV275110 OutboardMS-0729 3 Cylinder Liquid Cooled

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