GM Caprice 1990-1993 Repair Guide

Valve Guides

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The valve guides are not removable, they are an integral part of the cylinder head. Any cutting or grinding operation performed on the valve guides, should be done by a qualified machine shop.

REAMING VALVE GUIDES



If it becomes necessary to ream a valve guide to install with an oversize stem, a reaming kit is available which contains a oversize reamers and pilot tools.

When replacing a standard size valve with an oversize valve always use the reamer in sequence (smallest oversize first, then next smallest, etc.) so as not to overload the reamers. Always reface the valve seat after the valve guide has been reamed, and use a suitable scraper to brake the sharp corner at the top of the valve guide.

KNURLING



Valve guides which are not excessively worn or distorted may, in some cases, be knurled. Knurling is a process in which metal is displaced and raised, thereby reducing clearance. Knurling also provides excellent oil control.

This procedure should only be performed by a qualified machine shop.

STEM-TO-GUIDE CLEARANCE



Valve stem-to-guide clearance should be checked upon assembling the cylinder head, and is especially necessary if the valve guides have been reamed or knurled, or if oversize valve have been installed. Excessive oil consumption often is a result of too much clearance between the valve guide and valve stem.

  1. Clean the valve stem with lacquer thinner or a similar solvent to remove all gum and varnish. Clean the valve guides using solvent and an expanding wire-type valve guide cleaner (a rifle cleaning brush works well here).
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  3. Mount a dial indicator so that the stem is 90° to the valve stem and as close to the valve guide as possible.
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  5. Move the valve off its seat, and measure the valve guide-to-stem clearance by rocking the stem back and forth to actuate the dial indicator. Measure the valve stems using a micrometer and compare to specifications, to determine whether stem or guide wear is responsible for excessive clearance.
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