<VV> Rod Bearing Clearance Question

Tue Feb 7 20:48:10 EST 2012

Bob, Are you measuring with plastigauge or a micrometer and telescoping 
gauges? The service manual indicates a main brg. max. clearance of .0027 on 
# 1 and 2, and .0022 on # 3 and 4. IMHO .002 clearance on mains will work 
just fine. I have put many engines together with .002 clearance and had no 
problems.

If I remember my rates of thermal expansion for steel, when you raise a 
piece of round stock steel from 70 degrees F. to 200 degrees F. you will get 
a growth of .003" in dia. for every inch of diameter and .003" in length for 
every inch of length. So no! measuring at 40 is not going to change the 
diameter a full .001".

Jamie

-----Original Message----- 
From: Bob Gilbert
Sent: Tuesday, February 07, 2012 6:42 PM
To: virtualvairs at corvair.org
Cc: corvairs at cybrus.net
Subject:  Rod Bearing Clearance Question

Hi,

I've just started my 190 ci (3.l) build for my UltraVan and I'm using Bob
Helt's book plus the shop manual as my primary guides. Its' been 20 years
since I have done a complete engine like this so I'm using the books a lot!

The crankshaft was checked by both myself and a machinist we both found all
of the journals to be in spec and he recommended that all it needed was a
micro-polish.

I plastigauged the mains and the clearances were between the .0015 as per
Bob's book and .020. That was with standard size bearings.

However, I'm showing .002 clearance on the rod bearings. Bob says that .001
is ideal but I can't find anything to say whether .002 is enough to cause me
concern.

BTW, these measurements are being taken at about 40F. Is that enough to
cause the journals to shrink by .001?

Any thoughts or recommendations?

Regards,

Bob

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