undersized bearings

what would happen if i used 030 undersized main bearings on a stock crank? just wondering

 

Back to engine repair 101 for you. That won't even work as you wouldn't get the rod on the crank let alone get the crank to turn afterwards.
a .030 bearing takes having the crank turned .030 + the clearance needed to work.

 

that is what i thought...just have a bad headache and cant seem to think clearly.

having a hard time finding standard bearings for a engine im building. if my old bearings look ok what ya think about reusing old bearings?

 

Tighten the main bolts finger-tight and never start the engine, and it'll work fine.

 

Your first question is answered, you would have .030 inch nominal interference.

Although not the best, if your bearings are good AND you check the clearance is good, then reusing the bearings should be OK. Emphasis on the clearance is what is important, see answer number 1 above about interference.

 

Seriously?

 

...you didn't ask me...

Have you measured the crank? Is it actually still at standard?
I have 001 and 002 in stock...

.

 

Based on what has been posted there is no way to know the size and size variations present in the crank or the rod/main housings. Without doing some careful measuring there is no way to answer your question.

 

Not sure if this is a serious question. But, when a crankshaft journal is resized .030" under stock (.015" removed from the journal surface equals .030" in diameter) then the ***ociated bearings must match that dimension. That .030" refers to the diameter of the crankshft/bearing halves being reduced. The bearing inserts are thicker than stock. The added material is on the inner radius of the bearing. Not getting into the clearances required in this brief explanation. Just the basics of the question.
To mount .030" bearings on a stock crankshaft journal would be very much the same as putting a 13 inch tire on a 15 inch wheel.

 

If you can find under sized inserts for it you can find standard inserts for it. What do you need inserts for?

 

I think the term "undersize" confuses people sometimes. The bearing itself is actually oversize, to fit an undersize journal. (Although undersize bearings do exist to use on a oversize journal)

 

yes it does!!! espescially when youve had a long day at work and come home pondering about an engine build one has ahead of himself. i basically got myself confused. Got my answer....by many ppl. mainly 73rr

 

sure helped me understand

 

If you've numbered the old bearing shells to match the journal they came from then you can reuse them if they look OK and you do a Plastigage clearance check. But you cannot mix them up, or you'll have problems.