In the spirit of getting to the bottom of things, I phoned a friend of mine
who is friends with a guy at Perfect Circle about plastiguage. It turns out
that the stuff is accurate when they make it, but the plastisizer slowly
evaporates, with the effect that the thread shrinks slightly over time. The
problem is, not much time is required and the climate in which it is stored
affects the speed (hot=faster etc). Not having any at hand, I don't know if
they are dated on the package. The friend of a friend suggested that for
reliable results, buy "fresh" plastiguage and keep in the fridge or freezer
until use. Allow it to warm up before use, as condensation on the thread
(or on the journal yer measuring) will cause the thread to smear out wider
than it should. Measure all the journals in any engine with material from
the same package. If you have to remeasure a journal, do at least one other
so you can compare new with old (using the second as the standard) and see
if the reading have shifted. With these safeguards, you can get reliable
measurements to around plus or minus .5 thou. I'm not gonna throw my mics
away, but I figured that the real story on the material would benefit
everyone on the list more that simplistic do this or do thats. And I could
now live with using plastiguage in a pinch, which is change in attitude
from last week.
So. If you _must_ know the exact clearance of a bearing, use mics or the
like. If the job you're doing requires exact measurement, plus or minus a
half thou, use the methods above. This would be good for those expensive,
total rebuilds for a show car or weekend runner. If you're just building a
daily runner, and a couple of thou variance is ok, then just use the
plastiguage and don't worry too much about lot numbers and freshness, but
try to use the freshest possible.
Yers
Vern
_____________________________________________________________________
Vern Klukas I'm a little teapot
vernk@carver.dataflux.bc.ca or Short and...
ug141@freenet.victoria.bc.ca or
inkspot@carver.dataflux.bc.ca
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