Figure 3-14.—Excessively band-ground valve.assemble and disassemble a valve assembly. Before youreassemble a valve assembly, be sure to thoroughlyclean and inspect the valve spring. (Use kerosene ordiesel fuel for cleaning. NEVER use an alkalinesolution; it will remove the protective coating.) Thecondition of the surface of a valve spring is the bestindication of impending failure. (Use magnafluxing tohelp find cracks that would otherwise be invisible.)The free length of a valve spring should be withinthe limits specified in the manufacturer’s technicalmanual. If such information is not available, comparethe length of a new spring with that of the used spring.If the length of the used spring is more than 3 percentshorter than that of the new spring, replace the usedspring immediately. Remember, however, that loss ofspring tension will NOT always show up as a loss inoverall length. Springs may be the proper length, butthey may have lost enough tension to warrantreplacement.Figure 3-15.—Facing a valve on a lathe.Do not reinstall springs with nicks, cracks, orsurface corrosion. Replace them. To minimize corrosiveconditions, use clean lube oil, eliminate water leaks, andkeep vents open and cleanWORN VALVE KEEPERS AND RETAININGWASHERSWorn valve keepers and retaining washers mayresult if valve stem caps (used in some engines) areimproperly fitted Caps are provided to protect andincrease the service life of the valve stems. Troubleoccurs when the cap does not bear directly on the end ofthe stem, but bears instead on the valve stem lock or thespring retaining washer. This transmits the actuatingforce from the cap to the lock or the retaining washer,and then to the stem, causing excessive wear on the stemgroove and the valve stem lock As a result, the retainingwasher wiIl loosen and the valve stem may breakAn improper fit of a valve stem cap may be due tothe use of improper parts or the omission of spacershims. Steel spacer shims, required in some caps toprovide proper clearance, are placed between the end ofthe valve stem and the cap; leaving out the shims willcause the shoulder of the cap to come in contact with thelock. When you disassemble a valve assembly,determine whether or not shims are used. If shims areused, record their location and exact thickness. Valvecaps must be of the proper size, or troubles similar tothose resulting from shim omission will occur. Neverattempt to use caps or any other valve assembly partsthat are worn.BROKEN VALVE HEADSBroken valve heads usually cause damage to thepiston, liner, cylinder head, and other associated parts.This damage is generally repairable only byreplacement of these parts.3-11
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