Adam:

You are on the tight end of the spec. Is that what people think is best? We're shooting for the loose end in Dennis's motor.

 

not surprising about the clearance differences between using the dial indicator/micrometer and torquing down with plastigauge.......


I never used the dial indicator/mic route, just plastiguage in building my engines, but to each his own.....

glad to hear you found your clearances OK.


-Russ

 

Based upon what Greg Brown has posted, I could see wanting to go looser for a race engine. This motor is a street engine, so I was okay with the tolerance, particularly since we're talking about the mains here.

Are you shooting for 2.5 thou and Dennis' motor? What are going to do to dial in the clearance?

 

Actually it was the rod bearings, not the mains, we set loose - in fact, looser than the top of the spec. We used micrometers, but purpose-built ones that are very accurate. And I think that's just how the bearing set came out. I hope I'm not getting things mixed up (I was when I didn't read that you were talking mains). Jim Morton did all the measurements and calculations, although I did some under his guidance.

 

If I understand correctly you were using the bore dial gauge to measure the bore of the main bearing shells with the girdle in place and torqued down.

From a purely engineering perspective the fact that the bearing shell is unsupported by the crank (that would normally be there) Unless the shell is an absolutely perfect fit to the journal ie the gaps between halves just close when the girdle is torqued down, the shell is going to distort a little and lead to screwy readings. Measuring with the crank installed is the only way I can see that you can accurately measure the bore and by definition the clearance. Using plastigauge as you've discovered works.