4-CYCLE OVERHEAD VALVE ENGINES - Small Engine Discount

CONNECTING RODS
Some engine models have offset piston pins (not
centered) to centralize the combustion force on the
piston. When installing the connecting rod to the piston
it is imperative that the rod be installed correctly. On
engine models OVM, OHM, OHSK120 - 130, and
OVXL, the piston will have an arrow stamped on the
top of the piston. On OHV 13.5 - 17 engines, an arrow
is found on the piston skirt. The arrow on the top of
piston or on the piston skirt must point toward the
push rods or the carburetor side of the engine when
installing it in the cylinder. (diag. 32) If the piston does
not have an arrow, the piston can be installed either
direction on the connecting rod. On all engine
models, the match marks on the connecting rod
and cap must align and face out when installing
the piston assembly into the engine (diag. 33 &
34).
On horizontal shaft engines, oil dippers are attached
to the bottom connecting rod bolt. Some engines have
the oil dipper cast in the rod cap. Consult the
specification chart for the proper rod bolt torque when
installing the cap. The rod bolts should be torqued in
50 inch pound (5.65 Nm) increments until the specified
torque is achieved.
CRANKSHAFTS AND CAMSHAFTS
Inspect the crankshaft visually and with a micrometer
for wear, scratching, scoring, or out of round condition
at the bearing surfaces. Check for bends on the P.T.O.
end using a straight edge, square or a dial indicator.
CAUTION: NEVER TRY TO STRAIGHTEN A
BENT CRANKSHAFT.
The timing marks on the camshaft and the crankshaft
gears must be aligned for proper valve timing. (diag.
35 & 36).
MATCH MARKS
CAMSHAFT
GEAR TIMING
MARK
33
ARROW DIRECTION
BEVEL
CHAMFER TOOTH
CRANKSHAFT GEAR
MATCH
MARKS
32
34
PUNCH
MARK
SMALL
HOBBING HOLE
CRANKSHAFT
35
Camshafts
Check the camshaft bearing surfaces for wear using
a micrometer. Inspect the cam lobes for scoring or
excessive wear. If a damaged camshaft is replaced,
the mating crankshaft and governor gear should also
be replaced. If the crankshaft gear is pressed on it is
not serviceable and the crankshaft must also be
replaced.
Clean the camshaft with solvent and blow all parts
and passages dry with compressed air, making sure
that the pins and counterweights are operating freely
and smoothly on mechanical compression relief types.
OHH and OHSK50 - 70 engines use serviceable MCR
components and must be assembled as illustrated in
"Assembly" with a thrust washer placed on the
camshaft next to the compression release weight.
NOTE: Some OHH models used on chipper/
shredders may not require a compression release.
CAMSHAFT
GEAR
GEAR
KEYWAY
Not For Resale
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SMALL HOBBING
HOLE
36
COMPRESSION
RELEASE
MECHANISM
37
71