d-600 series

ENGINE TEAR DOWN AND REASSEMBLYTIPS
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 generousamount of oilto
theneedlebearingandrotatethe
crankshaft several times to work the
oil into the bearing.
ENGINE TEAR DOWN AND ,REASSEMBLY TIPS
0-600 SERIES
SAFETYWARNING
BEFOREPROCEEDINGWITH
DISASSEMBLY,ALWAYS DISCONNECT
SPARK PLUGLEADTO
PREVENT
ACCIDENTAL STARTING OF ENGINE. ALSO DRAIN ALL FUEL FROM
TANK INTO AN APPROVED SAFETY
CONTAINER
STORE IN A
WELL VENTED AREA.
NOTE
Keep assemblies intact whenever possible
tips.
in tear down.Observeassembly
Refer to Torque Reference Guide(Section
16) for correct torque requirements during
reassembly.
1974 AND EARLIER: Place fuel shut off
"OFF" position.Disconnectfuel
valvein
and primerhosesfromcarburetor.
Remove
seven screws securing shroud and gas tank
assembly and removeshroud.
SERVICE BULLETIN REFERENCES
8-9
ENGINETEAR
DOWN AND REASSEMBLY TIPS
0-600 SERIES
1975 AND LATER: Remove
shroud
mounting screws.Liftshroudfromengine
anddisconnectprimerhoseandfuelline
from shroud and fuel tank assembly.
1974 AND EARLIER: Remove three
air baffle
to
armature
screws
securing
plate. Disconnect kill switch lead from ignition switch and remove air baffle.
1975 AND LATER: Remove two Phillips
head screws and the ON-OFF switch mountingscrew,disconnectswitch
wire and remove air baffle.
Remove spark plug and install piston stop
tool no. 677389. Thisstop will alloweasy
removal Of flywheel nut. Removeflywheel
nut.
To removeflywheel; first removeflywheel
screen. Use a soft headed (plastic orrawhide) hammer andstriketop ofwide fin of flywheel. At the
same time apply upward pressure with your hand
at point opposite where hammer strikes. Loosen
flywheel as shown. Examine flywheel for wear or
damage. Check keyway for
distortion or cracking.
TEST A LAWN-BOY
CCAUTION; NEVER RUN OR
ENGINE WITHOUT THEAIR BAFFLE OR
SHROUD IN PLACE.WITHOUTTHEMA
PISTON SEIZURE WILL OCCUR.
8-10
SERVICE
BULLETIN
REFERENCES
REVISED 1983
ENGINETEAR
DOWN AND REASSEMBLYTIPS
D-600' SERIES
1975 AND LATER: Remove
shroud
mounting base by removing three 7/16 inch
hex head screws. One of these screws is
locatedunder
C-D module.Remove
C -D
moduletofacilitateshroud
mounting base
removal. On models equipped with alternator
remove
two alternator mounting
screws and remove alternator.
NOTE
The spark plug lead is routed between the cylinder and
shroud
mounting base. Use care when removing C-D module to prevent damaging the spark plug lead or rubber
connector.
Remove flywheel key. Use a pair of diagonal
pliers to roll key out of crankshaft keyway.
NOTE
Correct installation of key is important. If
installed incorrectly, possible cracking of
flywheel hub may occur.
Liftgovernor
yoke, weights and collar
off as anassembly.Set
aside carefully.
5adjustment
for serand
Section
Refer
to
vicing.
NOTE
spring from governor
lever. Lift up on lever
governor
to disengage
prongs
from slots in bracket. Remove governor lever and
nylon governorcollar.
Reinstall
governor
assembly
with
word "KEY" on yoke facing crankshaft keyway.
NOTE
Refer to Section 5 for proper installation
of governor collar.
Remove governor spring and steel thrust
washer.RefertoSection
5 forlubrication
of thrust washer.
SERVICE
BULLETIN
REFERENCES
Remove threemagnetoplatemounting
screws.
8-11
ENGINE TEAR DOWN AND REASSEMBLY TIPS
D - 6 0 0 SERIES
Install crankshaft guide tool, Part No. 602887
on top of crankshaft. This will retain the loose
needle bearingsin the magneto plate. Remove magneto plate and
bearing assembly.
NOTE
Always replace
seal
never
reuse
old seal.
NOTE
when reassemblingmagneto plate, coat
threads of mounting screws with LawnBoy nut and screw lock part no. 682301
and tighten securely. Refer to Section 16
for correct torque.
To replacebearing,insertbearingremoval tool Part No. 605082 in top of bearing
and drive it out with a soft headed hammer.
Hold plateinpalm
of your hand. If the
needlebearings
fall out of bearingrace,
count them and reinstall in bearing race by
using a heavy grease. Check bearing name,
stamped on bearing. If Torrington, it has
if Bremen, it has
thirty-three
needles;
thirty-two needles.
To install the bearing, insert bearing installer tool P a r t No. 605081 with the letteringfacingthe
head
tool. Drivebearing
in until the tool bottoms on plate. This
will
recess bearing slightly.
NOTE
Hold armature plate in hand
when removing or installing bearing. This will prevent
armature platedamage.
.-
After magneto plate has been reassembled on
short block, lubricate the new seal and slideit into
place on the crankshaft. Place seal installer part
no. 608976 on seal. Driveit in until tool bottoms on
top of plate.
Remove carburetor and reedplate assemblycomplete by removingfourscrews
securing reed plate to crankcase.
Use a large screwdriver or socket to loosen
connecting rod screws.Do not remove them.
8-12
SERVICEBULLETINREFERENCES
ENGINE TEAR DOWN AND ‘REASSEMBLY TIPS
D - 6 0 0 SERiES
Remove four 3/8 inchhexhead
screws
securing the cylinder to crankcase. Hit the
cylinderheadsharply
with a soft headed
hammer
do not use a steel hammer be-
The D-600 series C-D engine uses a high compression cylinder which cannot be interchanged
with cylinder on the D-400 engine. If new D-600
it is very
cylinder is installed onD-400engine
likely that piston seizure would occur because of
excessive heat. The new D-600 cylinder is pictured
at left and can be easily identified by the ribs cast
in form of letter “H” in cylinder.
D’-600SERIES
Remove cylinder by pulling it away from piston quickly. This prevents damage to piston and
rings.
Examine cylinder gasket closely.
It may
be positionedincorrectlyduringreassembly. That is, intake ports (seecylinderto
the left) can be partially blocked if gasket is
reversed. Correct positioning is illustrated
on cylinder to right.
INCORRECT
CORRECT
D-400 SERIES
I
The crankshaft should nowbe rotated until
rod cap is at lowest position.The rod cap may now
beremoved,allowing the needle bearings to fall
out. Needles should be counted. There must be 33.
Examine them carefully to make sure they are not
worn or damaged or have flat spots.
Remove piston and rod assembly. Note mating marks on the rod and cap andthe dovetail ends
of the bearing liners. ,These parts must be mated
accordingly for-reassembly. Liners must be centrally located in rod and cap.
Remove wrist pin retainerrings
and
drive wrist pin out. The
connecting
rod
contains 27 loose needles and care must be
taken in removing the wrist pin so that loose
needles a r e not lost. A 7/16 inch diameter
inserted to
by 3/4 inchdowel rodmaybe
prevent this. Bearing replacements are not
available. Must bepurchased
as part of
rod and bearing assembly.
The retainer ring opening must face
the piston dome o r piston skirt. This
will eliminate rings from popping out
during operation. Also, retainer has
a beveledside and flat side. When
installed, flat side should face away
from wrist pin.
reinstalled, apply acoating of OMC needle bearing
grease part no. 378642 or equivalent on the rod cap
and rod. Place 17 needles onrod cap and 16 on rod.
When reassembling connecting rod in piston, the
spacer lug ispositioned up towards "top" of piston.
The word "TOP" is diecastinskirt
of
it must
piston; when installedincylinder,
face up.
The strip bearing shown, no. 677963, is rodjournalbearing.
It includes 33 individual
needles.
Pull the crankshaft from the crankcase and wipe
connecting rod throw dry. Now, prepare strip needle bearing for installation by removing it carefully
from card and position it onyourindexfinger.
Wrap needles around throw. If the old needles are
8-14
Install crankshaft in crankcase. Reinstall
thrust washer in crankcaseof early models self propelled engine. On later models this thrust washer
was die cast , i n crankcase. Apply oilto piston rings,
wrist pin, and cylinder sleeve.Now gently place rod
on crankshaft journal and install rod cap. Install
new lock tabs on rod cap screws and install screws
and tighten just enough to retain needle bearings.
Do not bend locktabs a t this time.
SERVICE
BULLETIN
REFERENCES
ENGINE TEAR DOWN AND REASSEMBLYTIPS
D-600 SERIES
Stagger ring gaps (ends) over top of piston
and installring compressor, no610510, over head of
piston and compress rings. Place cylinder over piston head. Maintain pressure on ring compressor
until rings enter cylinder.
NOTE
Check
gasket.
It
must
not cover
intakeports.'
Also, cylindermust
be installed with exhaust ports down.
Center rod on wrist pin. Consult Chapter 16
for correct rod cap screw torque 60 inch-pounds,
and tighten in three steps of 20 inch-pounds each.
Rotate crankshaft aftereach step to check freedom
of assembly.
Bend lock tabs upagainst head of each screw.
If tabs do not fit flush against side of screw head,
do not turn
screw, form tab around corner.
NOTE
The rod cap screws, flywheel nut, spark
plug, and blade nut must be torqued
according to torque chart.See Chapter 16
for correct torque.
NOTE
Apply a generous amount of oil to the
needle bearing and rotate the crankto worktheoil
shaft several times
into the bearing.
SERVICE
BULLETIN
REFERENCES
8-15
PISTON AND CYLINDERWALLSSCORING
Most instances of piston & cylinder scoring
can be traced to lack of oil, use of improper
in cyloil fuel mixture, foreign particles
inder,heatingcaused
by plugged
cooling
fins, orexcessivecarbon
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 whichis
normal.
A
Piston B was also used in an engine with the correct fuel mixture, but was scored after a few
minutes or possibly severalhours 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 always adjacent to either the intakeor exhaust
ports. This resulted from small particles of metal
breaking awayfrom an intake or exhaust port.
This type of failure is covered bywarranty.
B
SCORING
DUE TO LACK
OF OIL
Piston C is heavily scored all aroundthe
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 ringgroovesindicateslack
of
oil. This i s not covered by warranty.
D
Lack of lubrication scoring will not always
result in light coloration of the piston dome
as the engine may have been run for some
and contime with sufficientlubrication
sequently,thepiston
dome will be dark in
color and resemble one which has been operating on proper fuel mix.
CARBON
Piston D is scored as a result of carbon build-up.
Accumulation of carbon and other deposits on the
piston skirt. Particles of carbonbreakingaway
from the exhaust ports, lodging betweenthe piston
skirt and cylinder results in scoring the piston
and/or cylinder. This is not covered by warranty.
In most cases, the rings will be partially or
completelyfrozen within the ring grooves,
and the piston will be discolored.
Carbon scoring usually results from the use of a
low gradeoil or an excessive amount of oil in the
mix or a lack of care and maintenance which is
owner's responsibility.
SERVICE
BULLETIN
REFERENCES
8-24
REVISED 1978