<VV> Engine building - bearing clearance

[Les]

On 1/21/2010 4:09 PM, bobhelt at aol.com wrote:
> 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
Yep, I figure I have lots of opportunity for error. Pretty sure I have 
std/.001 shells as they are marked on the back. Picked up plastigauge on 
the way home and will put it together and check asap. Unfortunately my 
wife's car suffered a semi major failure this afternoon so of course I 
have to fix that first.

Thanks,
Les