How To Measure Valve Guide Wear
Article by Vintage Vinny
There are several methods of checking valve guide wear on cylinder heads.
Professional machine shops rely on precision equipment to get the most accurate readings. But for those who don't have access to the proper tools, it's usually the 'wiggle test'.
The Low Buck Way
Wiggle Test - After compressing the valve and removing the keepers, collar, and spring, pull the valve completely out and wipe off any oil from the stem and guide, as it will give you a false tightness reading. Position the valve part-way (about an inch or so) out of the guide.
With fingertips only, rock it up and down, then side to side.
There will be either slight play (good) or too much play (not good).
If there's any detectable slop, it's time for new valve guides.
The problem is, if you haven't used this method before, how do you know what's acceptable?
If you happen to have a 2nd (or 3rd) cylinder head, and you know one is good (low mileage or recently rebuilt), you can to compare one to the other.
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Measuring With Precision Tools
The most accurate way to measure valve guide wear is with a split-ball gauge and outside micrometer or caliper.
Split-ball gauges, also called small-bore gauges or telescoping snap gauges, and are offered in various sizes.
How they function is, the gauge expands in the bore, and the user then locks it in place. Once removed, it gets measured with an outside micrometer or digital caliper to determine final hole size.
Once the guide I.D. (inside diameter) is obtained, measure the O.D. (outside diameter) of the valve stem. Subtract that figure from the I.D. of the guide and that's your clearance.
A 0 to 1" outside micrometer, such as this Mitutoyo, will measure down to 0.0001 inch. Cheaper tools often only measure down to 0.001 inch.
NOTE: Clearances are measured as total on round surfaces. Example: An 001" clearance means inside diameter of the hole is .001" larger than the shaft.
On valve guides, a general rule of thumb is .002" play is OK before replacement is needed. Check with a factory service manual for specs on your exact year and model.
NOTE: Exhaust guides always need a little bit more clearance, as they run hotter and expand.
Uneven Wear
Sometimes the I.D. of worn valve guides may not be perfectly round. They may have worn into an hour-glass, or 'bell mouth' shape. This is why a split-ball gauge is the best way to measure wear, as it will alert you of any irregular wear.
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The method that many engine builders use to determine guide wear is a combination of both the wiggle test and the split-ball way. Before measuring with a gauge and micrometer, do a wiggle test first. There's no extra work involved, because you've already removed the keepers, collar, and springs.
Dial Indicator
Another way to check valve guide clearance is to mount a dial indicator on the head so that the stem is at a 90 degree angle to the valve stem. You'll want it to be as close to the valve as possible. Next, move the valve off it's seat, rock the stem back and forth, and measure the clearance.
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Notes and Misc
There are instances where, even with proper measuring tools, precise measurement may not be attainable. In that case, it's best to replace anything questionable.
Measure Valve Stems
Don't forget to measure valve stems for wear! With a quality micrometer or caliper, measure each stem and compare with factory service manual specs.
If you're not accustomed to precision measuring tools, you can easily get false readings. But this is easily corrected by practice--measure the same one again and again, until you get the same exact results every time.
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Valve Guide Replacement Alternatives
If you do not have access to the necessary tools, or to a machine shop, there are several alternatives to removing and installing valve guides. Buying oversized valves is one option.
Choosing this method would still involve precise measuring, then slow and careful drilling/reaming of the old guide. The downside of oversize valves is that they may not be offered in the size you need, and if they are, they'll be more expensive than standard size valves.
K-Line Valve Guide Liners
K-Line states that their products provide an efficient and cost-effective solution to address worn or damaged valve guides. But there are drawbacks.
Jim Comstock, noted Norton specialist, explains the downside: "The valve will run hotter due to decreased heat transfer to the guide. Don't expect them to last as long as a correctly fitted, good quality new guide. Installation and sizing tools are expensive."
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