Figure 3-14.—Excessively band-ground valve.
assemble and disassemble a valve assembly. Before you
reassemble a valve assembly, be sure to thoroughly
clean and inspect the valve spring. (Use kerosene or
diesel fuel for cleaning. NEVER use an alkaline
solution; it will remove the protective coating.) The
condition of the surface of a valve spring is the best
indication of impending failure. (Use magnafluxing to
help find cracks that would otherwise be invisible.)
The free length of a valve spring should be within
the limits specified in the manufacturer’s technical
manual. If such information is not available, compare
the length of a new spring with that of the used spring.
If the length of the used spring is more than 3 percent
shorter than that of the new spring, replace the used
spring immediately. Remember, however, that loss of
spring tension will NOT always show up as a loss in
overall length. Springs may be the proper length, but
they may have lost enough tension to warrant
replacement.
Figure 3-15.—Facing a valve on a lathe.
Do not reinstall springs with nicks, cracks, or
surface corrosion. Replace them. To minimize corrosive
conditions, use clean lube oil, eliminate water leaks, and
keep vents open and clean
WORN VALVE KEEPERS AND RETAINING
WASHERS
Worn valve keepers and retaining washers may
result if valve stem caps (used in some engines) are
improperly fitted Caps are provided to protect and
increase the service life of the valve stems. Trouble
occurs when the cap does not bear directly on the end of
the stem, but bears instead on the valve stem lock or the
spring retaining washer. This transmits the actuating
force from the cap to the lock or the retaining washer,
and then to the stem, causing excessive wear on the stem
groove and the valve stem lock As a result, the retaining
washer wiIl loosen and the valve stem may break
An improper fit of a valve stem cap may be due to
the use of improper parts or the omission of spacer
shims. Steel spacer shims, required in some caps to
provide proper clearance, are placed between the end of
the valve stem and the cap; leaving out the shims will
cause the shoulder of the cap to come in contact with the
lock. When you disassemble a valve assembly,
determine whether or not shims are used. If shims are
used, record their location and exact thickness. Valve
caps must be of the proper size, or troubles similar to
those resulting from shim omission will occur. Never
attempt to use caps or any other valve assembly parts
that are worn.
BROKEN VALVE HEADS
Broken valve heads usually cause damage to the
piston, liner, cylinder head, and other associated parts.
This damage is generally repairable only by
replacement of these parts.
3-11
