<VV> Micrometers vs. Plastiguage

[Mark Durham]

Matt, to summarize, Bob. Is correct, but all you really need to know is
that plastiguage is made to give you the same clearances as a manual
measurement would give you with calibrated tools and a experienced
user. Mark Durham

Sent from my Windows Phone
From: BobHelt at aol.com
Sent: 4/3/2012 13:42
To: matthew_lockwood at hotmail.com; virtualvairs at corvair.org
Subject: Re: <VV> Micrometers vs. Plastiguage
Hi Matt,
I'd suggest that you be careful using the same specs for mic vs plastigage
measurements. The Shop Manuals all refer to making Plastigage measurements
and  their specs refer to that method. When Plastigaging, you are measuring
the  clearance of the crank journal to the bearing . That is the running
clearance. The SMs specs all are in the 0.001 to 0.003 inch range.

But by using micrometers to make these measurements you are measuring the
clearance on both sides of the journal and thus your clearance measurements
will  be twice the specs for any bearing. You are measuring the jourmal
diameter to  the bearing diameter. In addition, the Mics cause an increased
measurement error  since you must use TWO different measuring devices that may
or may not be  calibrated correctly. All that plus any human error in maiing
two  measurements.

Regards,
Bob Helt


In a message dated 4/3/2012 9:25:12 A.M. US Mountain Standard Time,
matthew_lockwood at hotmail.com writes:

Wondering if the specs are the same for using a mic vs  plastiguage.  So,
if the green manual calls for a clearance range of  .003-.006 on a crank
journal (from memory, I think thats right), using green  plastiguage in lieu of
mics should suffice,  correct?

Thanks,

Matt

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