Fitting Pistons
Needing to use a lot of old pistons of unknown material (aluminum
compound) I
had a tried and true method of determining the bore clearance.
I would boil a coffee can of water and slip a piston into the
water, wait a
couple minutes for the piston to heat up , then with gloves (desirable)
and a
suitable retractor remove the piston form the water and mic the
piston across
the skirt bottom both ways. Mic again just under ring grooves
both ways. By
comparing the results of the piston at room temperature and those
from the
boiling water you have the expansion rate. Add .003" to
the heated piston
dimensions and you will in most cases be right on the money for
racing
clearance.
"Never be beaten by Equipment"
Kas Kastner
My comments on the piston clearance should be clarified. The
best thing of
course is to contact the manufacturer and ask their advice on
THEIR pistons,
BUT, if you don't have any idea who made that devil, or when,
you might try my
method.
In the olden days the clearance for forged pistons was generally
about
.006" and there was only one company that I knew that had
the new aluminum
compounds. That was Cosworth and at that time they didn't want
to know about
little guys racing funny little cars from out nowhere..
"Never be beaten by Equipment"
Kas Kastner
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