Kohler ECV940 Service Manual page 134

Disassembly/Inspection and Service
After cleaning, check fl atness of cylinder head and
corresponding top surface of crankcase using a
surface plate or precision straight edge and feeler
gauge. Maximum allowable out of fl atness is 0.076 mm
(0.003 in.).
Carefully inspect valve mechanism parts. Inspect valve
springs and related hardware for excessive wear or
distortion. Check valves and valve seat area or inserts
for evidence of deep pitting, cracks, or distortion. Check
clearance of valve stems in guides.
Hard starting or loss of power accompanied by high
fuel consumption may be symptoms of faulty valves.
Although these symptoms could also be attributed to
worn rings, remove and check valves fi rst. After removal,
clean valve heads, faces, and stems with a power wire
brush.
Then, carefully inspect each valve for defects such as a
warped head, excessive corrosion, or a worn stem end.
Replace valves found to be in bad condition.
Valve Guides
If a valve guide is worn beyond specifi cations, it will not
guide valve in a straight line. This may result in burnt
valve faces or seats, loss of compression, and excessive
oil consumption.
To check valve guide-to-valve stem clearance,
thoroughly clean valve guide and, using a split-ball
gauge, measure inside diameter of guide. Then, using
an outside micrometer, measure diameter of valve stem
at several points on stem where it moves in valve guide.
Use largest stem diameter to calculate clearance by
subtracting stem diameter from guide diameter. If intake
clearance exceeds 0.038/0.076 mm (0.0015/0.0030
in.) or exhaust clearance exceeds 0.050/0.088 mm
(0.0020/0.0035 in.), determine if valve stem or guide is
responsible for excessive clearance.
Maximum (I.D.) wear on intake valve guide is 7.135
mm (0.2809 in.) and 7.159 mm (0.2819 in.) for exhaust
guide. Guides are not removable but can be reamed
0.25 mm (0.010 in.) oversize. Valves with 0.25 mm
oversize stems must then be used.
If guides are within limits but valve stems are worn
beyond limits, install new valves.
134
Valve Seat Inserts
Hardened steel alloy intake and exhaust valve seat
inserts are press fi tted into cylinder head. Inserts are
not replaceable but can be reconditioned if not too badly
pitted or distorted. If cracked or badly warped, cylinder
head should be replaced.
Recondition valve seat inserts following instructions
provided with valve seat cutter being used. Final cut
should be made with an 44.5° cutter as specifi ed for
valve seat angle. Cutting proper 45° valve face angle
as specifi ed, and proper valve seat angle (44.5°, half of
full 89° angle), will achieve desired 0.5° (1.0° full cut)
interference angle where maximum pressure occurs on
outside diameters of valve face and seat.
Lapping Valves
Reground or new valves must be lapped in, to provide
proper fi t. Use a hand valve grinder with a suction cup
for fi nal lapping. Lightly coat valve face with a fi ne grade
of grinding compound, then rotate valve on its seat with
grinder. Continue grinding until a smooth surface is
obtained on seat and on valve face. Thoroughly clean
cylinder head in soap and hot water to remove all traces
of grinding compound. After drying cylinder head, apply
a light coating of SAE 10 oil to prevent rusting.
Valve Stem Seals
These engines use valve stem seals on intake and
exhaust valves. Always use new seals when valves
are removed from cylinder head. Seals should also be
replaced if deteriorated or damaged in any way. Never
reuse an old seal.
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