4-CYCLE OVERHEAD VALVE ENGINES - Small Engine Discount

CYLINDER HEAD AND VALVE TRAIN
SERVICE
3
Check the cylinder head for warpage by placing the
head on a precision flat surface. If warped in excess
of .005" (.127mm), replace the head. Slight warpage
can be corrected by placing a sheet of #400 wet /dry
sandpaper on a precision flat surface and rubbing the
head gasket surface in a circular pattern until the entire
gasket surface shows evidence of sanding. A small
amount of honing oil on the sandpaper will make it
easier to slide the head. Always replace the head
gasket and torque the head bolts in 60 inch pound
(6.7 Nm) increments in the numbered sequence
torques in specification section (diag. 23 & 24).
1
4
2
2
TORQUE SEQUENCE
OVRM / OHH, OHSK50 - 70
4
5
23
Valves, Springs, And Push Rods
The valves should be checked for proper lash, sealing,
and wear. Valve condition is critical for proper engine
performance. Valve lash should be checked before
removal of the engine head if any of the following
conditions are experienced; a popping is heard through
the intake or exhaust, an engine kickback is
experienced, or when excessive valve train noise is
heard.
Valve lash (between the rocker arm and valve stem)
should be set or checked when the engine is cold. The
piston should be at T.D.C. on the compression stroke
(both valves closed). See specification section.
When servicing the valves, all carbon should be
removed from the valve head and stem. If the valves
have been checked and are in a usable condition, the
valve face should be ground using a valve grinder to a
45 degree angle. If after grinding the valve face the
margin is less than 1/32 of an inch (.794 mm), the
valve should be replaced (diag. 25).
Valves are not identical. Valves marked "EX" or "X"
are installed in the exhaust valve location. Valves
marked "I" are installed in the intake valve location. If
the valves are unmarked, the smaller valve (head) is
installed in the exhaust valve location.
If the spring has dampening coils, the valve spring
should be installed with the dampening coils away from
the valve cap and retainers (diag. 26).
The valve springs should be checked for both ends
being parallel and the free length being at least 1.105"
(28.067 mm) for OHH and OVRM engines, 1.980"
(50.292 mm for OHM, OVM, OHSK, OVXL, and OHV
engines when the valves are removed for service.
Replace the springs if necessary.
The push rods should be checked for straightness and
the ends for wear. If the push rod ends are worn or
damaged, inspect the corresponding rocker arm socket
or valve lifter for wear. Replace if necessary.
5
1/32"
(.794 mm)
3
6
TORQUE SEQUENCE
OHV 11 - 17, OHM, OHSK80 - 130
MINIMUM
DIMENSION
STEM
FREE LENGTH
OVRM/OHH/
OHSK50-70
1.105" (28.067 mm)
MARGIN
ALL OTHERS 1.980" (50.292 mm)
45 0
FACE
1
DAMPENING COILS
LOCATED CLOSER
TOGETHER
THIS END MUST FACE
TOWARD THE
STATIONARY PART
OF THE ENGINE
(CYLINDER HEAD)
24
25
26
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