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.

Whether the causes of broken valve heads are mechanical deformation or metal fatigue, you must take every precaution to prevent their occurrence. If a valve head breaks loose, be sure to make a thorough inspection of all associated parts before you replace the valve.