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Re: I need to use/borrow a good bore guage]

Subject: Re: I need to use/borrow a good bore guage]
From: Larry Colen <>
Date: Wed, 23 Aug 2006 10:09:53 -0700
On Wed, Aug 23, 2006 at 07:53:10AM -0400, Peter  Ryner wrote:
# Larry,
# The best way to check the clearance is with plastigage.  It is a thin piece

Actually plastigage is considered to be not as good of a way to check
clearances. The manufacturing tolerances on it are not as tight, plus
the age of it can affect how it behaves. The reason that plastigage is
usually used in home engine rebuilds is that it costs is that it costs
a few dollars, rather than the few hundred dollars that the good
measuring tools cost.

# of plastic that goes on the journal before you put the cap on.  After
# installing the cap and torquing to proper specs, the cap is taken off and
# the plastic is measured against a scale that comes with the gage.  Available

I'm very  familiar with it. I've installed new bearings something like
half a dozen or a dozen times in various motors.

# at most auto stores.  I'm not an expert on engine tolerances, but I'd be
# concerned about using a tolerance tighter than the spec.  The tolerance is
# not just to make room for oil, it also allows proper clearance after the
# disimilar metals expand under heat.  Too tight a tollerance may cause the
# two metals to overheat causing instant meltdown of the crank.  Personally I
# would shoot for the minimun tolerance, not less.

You make a good point. I'm not an expert either, that's why I was
taking the advice of someone who machines cranks for a living. The
clearances he gave aren't a lot smaller than stock, but his tolerances
are a lot tighter:
     Nominal  Armando
Rods 1.9-3.9  1.5-1.8
Main 1.3-5.5  2.0-2.2

Software that holds your hand is one thing, software that holds your
hand and won't let go is really, really annoying.
Larry Colen     

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