What is the main bearing bore diameter tolerance for being out of round in the block (without bearings installed)?

The measurement I?m getting using a mic and dial bore gauge is 2.4905? straight up and down (90 degrees away from the cap parting line) But very near the parting line the bore is .0020? larger which seems like a lot. Hoping to avoid a line bore or hone. The engine in question is a 1965 Chevrolet 292. Hoping for help even through this is not a third gen. engine.

 

Spec is 2.4906/2.4916. If you're .002 out, it's gonna need line bored..

 

What's the application? Just a stock rebuild low compression? Yes, in a perfect world, but I've seen many, just about every sbc mains are out of round. Remember it rides on oil. If you arnt spinning it up crazy and have lower compression, I wouldn't be afraid to run it. Also, it takes a very skilled builder to accurately measure in tenths. Meaning, .0001.
I'm not going to tell you to run it, it's up to you, but chances are it will be fine. Unless its more like .005 out of round. Then for sure have it line honed.
hope this helps.

 

Sense you have a bore gauge, I'd measure with bearings installed and caps torqued. Measure crank writing them all down, then measure mains with bearings installed. Then do some math.

may as well do rods also same way. Good practice to measure everything

 

Remember when you have your mains bored, everything gets closer to cam. Now were not talking much but it does. And who knows how straight mains are with cam, etc.

 

I agree.

 

This engine came out of and is going back into a truck. It will be low compression stock rebuild - low RPM. Now that I have the main bore size I will recheck them to verify the initial measurements. As you suggested, I will also install the bearings and check clearances relative to the crankshaft with the dial bore gauge.

Thanks for helping me out, much appreciated.