SECTION 8 POWERHEAD ENGINE TEAR DOWN AND REASSEMBLY TIPS

D-400 SERIES Refer to Section 14 for special "D" engine tools needed for tear down and reassembly.

Keep assemblies intact whenever possible in tear down. Obseve assembly tips. Refer to Torque Reference Guide Section 16 for correct torque settings dining assembly.

SAFETY WARNING Disconnect high tension lead from spark plug to prevent accidental start- ing of engine. 1974 AND EARLIER: Disconnect gas

line from carburetor and remove complete engine shroud, gas tank, gas tank bracket, primer bar and air baffle. Replace shroud screws in the same location from which they were removed.

1975 AND LATER: Remove engine shroud mounting screws. Remove the re- tainer clip from the speed control opening

the shroud and disconnect the fuel line and primer hose from the shroud and fuel tank assembly. Tilt the shroud to maneuver the speed control knob through shroud opening and remove shroud.

in the rear of the shroud. Carefully lift

Remove spark plug and install special piston stop tool No. 677389. This stop will allow easy re- moval of flywheel nut. Remove flywheel screen and flywheel nut.

I

1975 AND LATER

SERVICE BULLETIN REFERENCES 8-1

ENGINE TEAR DOWN AND REASSEMBLY TIPS D - 4 0 0 SERIES

To remove flywheel; lift up on one side and strike top of thick fin on opposite side with soft hammer (plastic or rawhide). Remove flywheel. Check flywheel for damaged fins and keyway for distortion, cracks or damage. Replace if damaged.

Remove four screws securing air baffle to armature plate and remove air baffle.

1975 and later models are equipped with a plastic air baffle. Exercise care when removing assembly from armature plate.

Remove flywheel key. Use a pair of diagonal pliers to roll the key out of crankshaft keyway.

FL

I 1975 AND LATER I

I

RIGHT WRONG

NOTE

Correct installation of key is important.

8-2 SERVICE BULLETIN REFERENCES

ENGINE TEAR DOWN AND REASSEMBLY TIPS D-400 SERIES

Lift governor yoke, weights and collar off as an assembly. Set aside carefully. Refer to Section 5 for adjustment and servicing.

NOTE

Reinstall governor assembly with word “KEY” on yoke under crankshaft keyway.

Remove governor spring and steel thrust washer. Refer -to Section 5 for lubrication of thrust washer.

Unhook variable speed spring from gov- ernor lever. Lift up on governor lever to disengage prongs from slots in dust cover. Remove governor lever and nylon thrust collar. Refer to Section 5 for proper in- stallation of thrust collar.

Remove by taking screws.

dust cover out three

Push small end of spark advance fly- weight toward crankshaft. Hold tension of spring against crankshaft and return fly- weight to original position. Allow smaller end of flyweight to drop down. Remove pin and spring.

REASSEMBLY TIP Install flyweight with words “SHAFT KEYWAY THIS END” (smaller end) toward crankshaft key- way. Reinstall pin and spring properly - clip on end must be installed horizontally under flange in narrow end of flyweight.

SERVICE BULLETIN REFERENCES 8-3

ENGINE TEAR DOWN AND REASSEMBLY TIPS D - 4 0 0 SERIES

@Slide flyweight and cam off crankshaft.

Remove three magneto plate mounting screws.

NOTE

Apply Lawn-Boy nut and screw lock part number 682301 to threads of magneto plate mounting screws prior to reassem- bly. Tighten screws to correct torque, refer to Section 16 for correct torque.

Needle bearings in magneto plates of some models are not retained. To hold them in place dur- ing removal, and also to protect the main bearing seal, insert crankshaft guide tool, part number 602887 as shown. Remove armature plate.

A bearing containing 25 needles (largest bear- ing pictured) was used through 1969 production. A different magneto plate and bearing assembly was

i

8-4 SERVICE BULLETIN REFERENCES

ENGINE TEAR DOWN AND !REASSEMBLY TIPS -D-400 SERIES

To replace bearing, remove seal. Insert blade end of screwdriver under seal and pry up. Do not damage the magneto plate casting.

@ Insert bearing removal tool Part No. 605082 and drive bearing out with soft headed hammer. If magneto plate is resting on hard surface, plate may become damaged; therefore, hold plate in palm of hand.

@ Install bearing by inserting bearing on installer tool with lettering facing head of tool. Drive bearing in, holding plate in hand, until tool bottoms on plate, recessing bearing slightly.

BEARING INSTALLER ! PART NO. 605081

After magneto plate has been reassembled on short block, lubricate the new seal and slide it into place on the crankshaft. Place seal installer Part No. 608976 on seal. Drive it in until tool bottoms on top of plate.

NOTE Always replace seal never reuse.

SERVICE BULLETIN REFERENCES REVISED 1977. 0 5

ENGINE TEAR DOWN AND REASSEMBLY TIPS D-400 SERIES

@Remove carburetor and reed plate as- sembly complete by removing four (4) screws securing reed plate to crankcase.

NOTE The upper left hand screw has no lockwasher. This is to provide clearance between throttle arm and head of screw.

Use a large screwdriver or a socket to loosen (do not remove) the connecting rod screws. Lock tabs have to be bent away from screws first.

NOTE Do not reuse lock tabs. Always replace them with new ones.

Remove four (4) 3/8 inch hex head screws se- curing cylinder to crankcase. Hit cylinder head sharply with soft headed hammer (plastic or leather) a steel hammer will damage the casting. Remove cylinder by pulling away from piston quickly. This prevents the piston and rings from binding and becoming damaged.

Examine cylinder gasket closely. It may be positioned incorrectly during reassem- bly. Intake ports can be partially blocked (refer to cylinder on the left) if gasket is reversed. Correct positioning is illustrated on cylinder on the right.

INCORRECT CORRECT 8-6 SERVICE BULLETIN REFERENCES

ENGINE TEAR DOWN AND ‘REASSEMBLY TIPS D - 4 0 0 SERIES

Correct cylinder for D-400 series engine is shown at right. Cylinder a t left (ribs cast in letter “H” form) to be used only on D-600 series engine. If used on D-400 engine, failure will occur.

Position crankcase so piston dome is facing up. Crankshaft should be rotated until jour- nal is at lowest position. Remove rod cap, allowing needle bearings to fall out. Nee- dles should be counted. There must be 33. New lock tabs should be installed on rod cap screws for reassembly.

Remove piston and rod assembly. Note mat- ing marks on rod and cap, and the dovetail ends of the bearing liners. These parts must be mated for reassembly. Liners must be centrally located in rod and cap.

DOVETA ENDS

MATING MARKS

. D - 6 0 0 S E R I E S D-400 S E R I E S

NOTE Engines produced prior to 1970 contained three-ring piston those produced after contained two-rings on piston. The two- ring piston and rod assembly contains 27 loose needles in wrist pin end of rod. The three-ring piston and rod contains a bronze bearing in wrist pin end of rod. Care must be taken in removing wrist pin so that loose needles are not misplaced or lost. A 7/16” diameter x 3/4” dowel rod may be inserted to prevent this. This is of utmost importance, since the needle bear- ing assembly is not available as a service replacement.

Remove wrist pin retainer rings and drive wrist pin out.

When reassembling connecting rod in piston, the spacer lug is positioned up towards “top” of

SERVICE BULLETIN REFERENCES

piston. NOTE

When replacing retainer rings, open- ing must face piston dome or towards bottom of piston skirt. This will eliminate retainer rings from pop- ping out during operation. Retainer has beveled side and flat side. When installed, flat side must face outside of piston.

The word “TOP” is diecast in the skirt of the piston; when installed in Cylinder, it must face up.

8-7

ENGINE TEAR DOWN AND REASSEMBLY TIPS D-400 SERIES

Pull crankshaft from crankcase and wipe con- necting rod-throw dry. Prepare strip needle bear- ing, part number 677963 (includes 33 needles) for installation by removing it carefully and position it on index finger. Wrap needles around throw. If old needles are re-installed, apply a coating of OMC needle bearing grease part number 378642 or equiv- alent on rod cap and rod. Place 17 needles on rod cap and 16 on rod.

Install crankshaft in crankcase. Apply oil to piston, rings, wrist pin, and cylinder sleeve. Place rod on crankshaft journal and install rod cap. Tighten rod cap screws finger tight, i.e., just enough to retain nee- dle bearings. Do not bend lock tabs at this point.

Install ring compressor, part number 610510 over head of piston and compress rings. Place cylin- . der over piston head. Maintain pressure on ring compressor until rings enter cylinder.

NOTE

Check gasket. It must not be cover- ing intake ports. Cylinder must be installed with exhaust ports down.

Center rod on wrist pin. See Section 16 for correct rod cap screw torque (60 inch-pounds), and tighten screws in three steps of 20 inch-pounds each. Rotate crankshaft after each step to check freedom of assembly.

NOTE

Torque rod cap screws, flywheel nut, spark plug, and blade nut according to torque chart in Section 16.

ENGINE TEAR DOWN AND REASSEMBLY TIPS D - 4 0 0 SERIES

Bend lock tabs up against screw heads. If tabs do not fit flush against side of screw head, do not turn screw merely form tab around corner.

NOTE

Apply a generous amount of oil to the needle bearing and rotate the crankshaft several times to work the oil into the bearing.

ENGINE TEAR DOWN AND ,REASSEMBLY TIPS 0-600 SERIES

SAFETY WARNING BEFORE PROCEEDING WITH DIS- ASSEMBLY, ALWAYS DISCONNECT SPARK PLUG LEAD TO PREVENT ACCIDENTAL STARTING OF EN- GINE. ALSO DRAIN ALL FUEL FROM TANK INTO AN APPROVED SAFETY CONTAINER STORE IN A WELL VENTED AREA.

NOTE

Keep assemblies intact whenever possible in tear down. Observe assembly tips. Refer to Torque Reference Guide (Section 16) for correct torque requirements during reassembly.

1974 AND EARLIER: Place fuel shut off valve in "OFF" position. Disconnect fuel and primer hoses from carburetor. Remove seven screws securing shroud and gas tank assembly and remove shroud.

SERVICE BULLETIN REFERENCES 8-9

ENGINE TEAR-DOWN AND REASSEMBLY TIPS UTILITY MODELS

Refer to Section for special "D" engine tools needed for tear-down and reassembly.

SAFETY WARNING BEFORE PROCEEDING WITH DIS- ASSEMBLY, DISCONNECT SPARK

DENTAL STARTING OF ENGINE. ALSO DRAIN ALL FUEL FROM TANK INTO AN APPROVED SAFETY CONTAINER AND STORE IN A WELL VENTED AREA.

NOTE Keep assemblies intact whenever possible in tear-down. Observe as- sembly tips. Refer to Torque Ref- erence Guide Section 16 for correct torque settings during reassembly.

PLUG LEAD TO PREVENT ACCI-

Remove four (4) engine shroud mounting screws. Carefully lift the shroud and disconnect the fuel line and primer hose from the shroud and fuel tank assembly. Tilt shroud to remove.

Remove spark plug and install special piston stop tool part no. 677389. This will allow easy re- moval of flywheel nut. Remove flywheel screen. Screen must be removed to expose flywheel nut. Remove flywheel nut.

CAUTION NEVER RUN OR TEST A LAWN-BOY ENGINE WITHOUT THE AIR BAFFLE OR SHROUD IN PLACE. A PISTON SEIZURE WILL OCCUR.

8-16 SERVICE BULLETIN REFERENCES REVISED 1983

ENGINE TEAR-DOWN AND, REASSEMBLY TIPS UTILITY

To remove flywheel; use a soft headed (plastic or rawhide) hammer and strike flywheel wide fins to loosen flywheel. Remove flywheel. Check fly- wheel for broken fins, damage or cracks.

MODELS

Remove flywheel key. Use a pair of diagonal pliers to roll the key out of crankshaft keyway.

Remove four screws securing air baffle to armature plate and remove air baffle.

NOTE

Utility models a r e equipped with a plastic air baffle. Exercise care when removing assembly from arma- ture plate.

SERVICE BULLETIN REFERENCES

a NOTE

Correct installation of key is im- portant.

8-17

ENGINE TEAR-DOWN AND REASSEMBLY TIPS UTILITY MODELS’

Lift governor yoke, weights and collar Remove dust cover by removing three off as an assembly. Set aside carefully. attaching screws. Refer to Section 5 for adjustment and ser - vicing.

NOTE

Reassembly Tip Reinstall governor assembly with word “KEY” on yoke under crankshaft keyway.

Remove governor spring and steel thrust washer. Refer to Section 5 for lu- brication of thrust washer.

Push Small end of spark advance fly- weight toward crankshaft. Hold tension of spring against crankshaft and return fly- weight to original position. Allow smaller end of flyweight to drop down. Remove pin and spring.

8-18 SERVICE BULLETIN REFERENCES REVISED 1978

ENGINE TEAR-DOWN AND' REASSEMBLY TIPS MODELS UTILITY

Slide flyweight and cam off crankshaft.

Remove three (3) magneto plate mount- ing screws.

NOTE

Apply Lawn-Boy nut and screw lock part no. 682301 to threads of magneto plate mounting screws prior to reassembly. Tighten screws to correct torque, refer to Section 16 for correct torque.

Needle bearings in magneto plate are not retained. To hold them in place during removal, insert crankshaft guide tool, part no. 602887 as shown Remove magneto plate.

'TO replace bearing, remove seal using seal re- mover tool part no. 681867.

SERVICE BULLETIN REFERENCES 8-19 REVISED 1978

ENGINE TEAR-DOWN AND REASSEMBLY TIPS UTILITY

Insert bearing removal tool part no. 605082 and drive bearing out with soft headed hammer. If magneto plate is resting on hard surface, plate may be damaged; therefore, hold plate in palm of hand.

Install bearing by inserting bearing on installer tool with lettering facing head of tool. Drive bearing in, holding plate in hand, until tool bottoms on plate, recessing bearing slightly.

MODELS'

After magneto plate has been reassembled on short block, lubricate the new seal and slide it into place on the: crankshaft. Place seal installer part no. 608976 on seal. Drive it in until tool bottoms on top of plate.

NOTE

Always, replace seal never reuse old seal.

Remove carburetor and reed plate as- sembly by removing four (4) screws se- curing reed plate to crankcase.

The upper left hand screw has no This is to provide lockwasher

clearance between throttle arm and head of screw.

8-20 SERVICE BULLETIN REFERENCES REVISED 1978

ENGINE TEAR-DOWN’ AND REASSEMBLY TIPS UTILITY

Use a large screwdriver or socket to loosen (do not remove) the connecting rod screws. Lock tabs do have to be bent away from screws first.

Remove four (4) 3/8 inch hex head screws se- curing cylinder to crankcase. Hit cylinder head sharply with soft headed hammer (plastic or leather) a steel hammer will damage the casting. Remove cylinder by pulling away from piston quickly. This prevents damage to piston and ring assembly.

Examine cylinder gasket closely. It may be positioned incorrectly during reas- sembly. Intake ports can be partially blocked (refer to cylinder on the left) if gasket is reversed. Correct positioning is illustrated on cylinder on the right.

INCORRECT CORRECT

MODELS

Correct cylinder for D-400 series engine is shown at right. Cylinder at left (ribs cast in form of letter “H”) to be used only on D-600 series engine. If used’ on D-400 engine, failure will occur.

600 SERIES 400 SERIES Position crankcase so piston dome is facing up. Crankshaft should be rotated until journal is at lowest position. Remove rod cap, ‘allowing needle bearings to fall out. Needles should be counted. There must be 33. New lock tabs should be installed on rod cap screws for reassembly.

Remove piston and rod assembly. Note mat- ing marks on rod and cap, and the dovetail ends of the bearing lines. These parts must be mated for reassembly Liners must be seated in rod and cap correctly.

SERVICE BULLETIN REFERENCES REVISED 1978

ENGINE TEAR-DOWN AND REASSEMBLY TIPS UTILITY

Remove wrist pin retainer rings and drive wrist pin out. To remove wrist pin use special tool part no. 602884.

When reassembling connecting rod in piston, the spacer lug is positioned up towards "top" of piston.

NOTE When replacing retainer rings, opening must face piston dome or towards bottom of piston skirt. This will eliminate retainer rings from popping out during operating. Retainer has beveled side and flat side. When installed flat side must face away from wrist Din.

NOTE The word "TOP" is diecast in the skirt of the piston; when installed in cylinder, it must face up.

Pull crankshaft from crankcase and wipe con- necting rod-throw dry. Prepare stripe needle bear- ing, part no. 677963 (includes 33 needles) for instal- lation by removing it carefully and position it on index finger. Wrap needles around throw. If old needles are re-installed, apply a coating of Needle Bearing Grease part no. 378642 or equivalent on rod cap and rod. Place 17 needles on rod cap and 16 on rod.

MODELS

Instali crankshaft in .crankcase. Apply oil to piston, rings, wrist pin, and cylinder sleeve. Place rod on crankshaft journal and install rod cap. Tighten rod cap screws finger tight, i.e., just enough to retain needle bearings. Do not bend lock tabs at

Stagger ring gaps (ends) on top of piston ap- proximately 30° apart and install ring compressor, part no. 426020 over head of piston and compress rings. Place cylinder over piston head. Maintain pressure on ring compressor until rings enter cylin- der.

NOTE

Check: gasket. It must not be cov- ering intake ports. Cylinder must be installed with exhaust ports down.

SERVICE BULLETIN REFERENCES REVISED 1978

ENGINE TEAR-DOWN AND REASSEMBLY TIPS UTILITY MODELS

Center rod on wrist pin. See Section 16 for Bend lock tabs up against head of each screw. correct rod cap screw torque (60 inch-pounds) and If tabs do not fit flush against head of screw, do tighten in three steps of 20 inch-pounds each. not screw merely form tab around corner. Rotate crankshaft after each step to check freedom of assembly.

NOTE

Torque rod cap screws, flywheel nut, spark plug and blade nut ac- cording to torque specifications in Section 16.

NOTE

Apply a generous amount of oil to the needle bearing and rotate the crankshaft several times to work the oil into the bearing.

PISTON AND CYLINDER WALLS SCORING Most instances of piston & cylinder scoring can be traced to lack of oil, use of improper oil fuel mixture, foreign particles in cyl- inder, heating caused by plugged cooling fins, or excessive carbon build-up in the cylinder exhaust ports.

Piston A has been used in an engine which has a correct fuel-oil mixture. Note there is no sign of scoring, the rings are free in their grooves, and the top of the piston shows dark discoloration which is normal.

Piston B was also used in an engine with the cor- rect fuel mixture, but was scored after a few minutes or possibly several hours of operation. The top of the piston is dark in color, which is normal. Also, a film of oil is found in the ring grooves and on the inside of the piston which further indicates proper fuel-oil mix. Note the scoring is isolated to a particular area on the piston skirt. Scoring is al- ways adjacent to either the intake or exhaust ports. This resulted from small particles of metal breaking away from an intake or exhaust port. This type of failure is covered by warranty.

Piston C is heavily scored all around the skirt. This piston was run in an engine with a lack of lubrication. The light color on the top of the piston and lack of oil inside the piston and ring grooves indicates lack of oil. This i s not covered by warranty.

Lack of lubrication scoring will not always result in light coloration of the piston dome as the engine may have been run for some time with sufficient lubrication and con- sequently, the piston dome will be dark in color and resemble one which has been op- erating on proper fuel mix.

Piston D is scored as a result of carbon build-up. Accumulation of carbon and other deposits on the piston skirt. Particles of carbon breaking away from the exhaust ports , lodging between the piston skirt and cylinder results in scoring the piston and/or cylinder. This is not covered by warranty.

A

B

SCORING DUE TO LACK

OF OIL

D

CARBON

In most cases, the rings will be partially or completely frozen within the ring grooves, and the piston will be discolored.

Carbon scoring usually results from the use of a low grade oil or an excessive amount of oil in the mix or a lack of care and maintenance which is owner's responsibility.

8-24 SERVICE BULLETIN REFERENCES

REVISED 1978