<VV> Micrometers vs. Plastiguage

[jvhroberts at aol.com]

 I do it both ways, often. The biggest advantage of Plastigage is it's a lot harder to make math errors! 

And yes, it measures total clearance. Fortunately, Plastigage is resistant enough to deformation that it'll push the crank journal over to the other side from it no matter what. You'd be surprised how flexible a crankshaft is when you're only talking a few thousanths of an inch! Same goes for the crankcase. 

But the micrometer method allows you to also measure out of round, both of the journal and of the case and rod bores. This is difficult to do well (but not impossible) with Plastigage. 

Clearance is always defined as bearing ID minus journal OD. Regardless whether or not you agree with this definition, that's how the industry defines it. 

 

John Roberts
 

 

-----Original Message-----
From: Daniel Monasterio <dmonasterio at hotmail.com>
To: roboman91324 <roboman91324 at aol.com>; VirtualVairs <virtualvairs at corvair.org>; Bob Helt <bobhelt at aol.com>
Sent: Wed, Apr 4, 2012 10:22 am
Subject: Re: <VV> Micrometers vs. Plastiguage



I use plastigage all times but, have a concern about both ways. If rotating 
member is resting on bearing ( 0 clearance ), the plastigage measures the total 
clearance, same as a micrometer... isn't it ?This means, at least to me, that, 
if plastigage and/or micrometer give a total clearance of, say, 0.002", in fact 
when rotating there is a clearance (or oil film around) of 0.001"... isn't ?
Just trying to have this clear on my mind.
Daniel Monasterio 



<< Yes, the Plastigage measures the clearance between the  rotating member and  
the bearing while the micrometers measure and include the  clearance on 
 both sides.>>

 		 	   		  
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