<VV> Engine building - bearing clearance

[bobhelt at aol.com]

In a message dated 1/21/2010 1:55:42 P.M. US Mountain Standard Time,  
corvair at mts.net writes:

I am  measuring the inside of the bearing bore in a torqued block, using 
snap gauges  and a micrometer.

I measure the crank, the journal is (for example, and  from memory) 
2.0985". I measure the corresponding bore with snap gauge (.001  shells installed), 
then mike the gauge, and get 2.0991".

So my  clearance is .0006 - too small.

I want .0010 more clearance, so I  substitute 2 STD shells instead of .001 
shells.

Remeasure, and now the  bore measures 2.1011 and clearance is .0026" 
(pretty big).

That's what  makes me think that a single .001 shell takes away .001 
clearance and a pair  of them takes away .002.



Les,
As I see it there are two problems doing it that way. Either of which can  
be causing your measurement problem.
 
One, without a crank journal to force the shell against the alum case  
uniformly around the whole journal, you have a vairiable in your measurements.  
You are relying on the butting of the shell ends to fully seat the shell, 
and  this isn't sufficient always to seat the shells..
 
And also, trying to use a snap switch inside a circular path allows the  
snap sw to be offset slightly and not perfectly perpendicular the crank 
journal  axis and across the real diameter of the shells. It's easy to get the 
snap sw  off just a little in trying to measure the diameter exactly. 
 
Also, just wondering....are you sure you have the std and one under shells? 
 Possibly one or more shells are not what you think??????
 
Regards,
Bob Helt