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TM 10-3930-644-14&P
Carefully inspect the crankcase for cracks around the
Replace worn guides as required by using a suitable
exhaust valve areas.
driver and an arbor press from the combustion side to
the correct depth below the valve seat. Refer to Figure
Inspect spring coils for bright spots that may be an
4-3 and TOPIC 1. FITS AND TOLERANCES.
indication of spring weakness when found beyond the
closely spaced dampening coils at the spring ends.
Over-speeding the engine can cause this condition.
Replace any rusted, weak, cracked or broken springs.
Check the tension of each valve spring with a spring
scale designed for the purpose.  Refer to following
subparagraph 5. Valve Springs.
1. Valve Guides
Clean the valve stem guides, removing lacquer
or other deposits by running a valve guide
cleaner or wire brush through the guides.
Check guides for wear by using a "Go and No-
Go" plug gage, or a telescope gage and a 1"
micrometer.  Replace all guides that are worn
Figure 4-3. Distance from Block Face to Top of Valve
bell-mouthed and have increased .0015" in
Guide
diameter.
Refer to TOPIC 1.
FITS AND
TOLERANCES
for
maximum
diameter
CAUTION
permissible, to determine actual amount the
When replacing guides that are ferrox
diameter has increased.
When necessary,
coated, do not ream, since these are
remove all valve guides; use an arbor press and
all pre-reamed before being ferrox
press them out from the combustion chamber
coated  any  further  reaming  will
side with a driver slightly smaller than the O.D.
remove the coating.
of the valve guide.
2. Valve Seat Inserts
Valve guides are a press fit, and service guides
are especially machined to press in place and
The exhaust valve seat insert is held in place by
give correct stem clearance without further
a shrink fit.
machining. However, the valve seat MUST be
re-cut concentric with the new guide whenever
new guides are installed.
Figure 4-4. Removing Exhaust Valve Seat Insert
Figure 4-2. Removing Valve Guides
R-104-1
3-8

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