> so I understand that if as time passes, your valve clearances are decreasing .
> . that you can have valve seat recession.
>
> (at least that's what i think I understand. edumacate me if I'm wrong)
Nope, that's right. Everything else makes the clearance bigger as it wears,
only the valve seats (or face) make clearances smaller as they wear. And faces
rarely wear enough to be noticeable without burning a valve (which would cause
poor compression).
> What's going on when the valve clearances get bigger?
Generally normal wear throughout the valve train. Rocker pivots, rocker tips,
lifters, cam lobes, even valve stems. Even pushrods sometimes fail shorter.
> What if it happens over a relatively short period of time vs a long period of
> time? Does that mean anything?
Just means that something is wearing faster. Whether that's something to be
concerned about depends on how fast it is. I'd say a sustained change of over
.001" in 10-12k miles is cause for concern, but of course errors in measurement
may be larger than .001" so it might have to change in the same direction over
several years to be sure that's what's happening. Worn rockers can cause the
measurement to vary by maybe .003" or .004" without actually hurting anything;
and variations in measurement "feel" can account for another several thou.
Randall
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