Nobody talks about the nominal main bores size, just the clearances.

Crank journal is 57.00mm, ACL race bearings are 1.99mm each side, oil clearance is 0,04mm. So, the main bore should be 61,02mm, right?

I bought ACL race bearings and fitted main studs, but found out that half my engine block main bores need a slight thicker bearing. I'm still figuring out wether I should line bore it or stick with OEM bearings.

Looking for opinions from the experienced engine builders.

 

do they run increased mains bearing clearance for high power engines?

 

Yes.

I guess the main bores are 61,02mm, as crank is 57mm, bearings are 1,99 each and clearance is 0,04.

 

line boring is pretty expensive. if u have the money for it go for it but id try to make something work before i got a block line bored

 

whats the markings on your block? (there should be 5 numbers on the bottom of the block where the oil pan bolts on).
Mine was 1 2 2 2 1 (tolerances) and i had it line honed.
I'm guessing that "1" is 62.01mm, "2" is 62.02mm and "0" would be 62.00mm.
So my mains bore size would be 62.02+ mm.
With stock sized ACL bearings i was getting 0.09mm clearance.
I fitted 0.025 oversize ACL bearings, and i got 0.06-0.065mm clearance.
My crank is 56.99mm

done and done

hope that helps

 

Mine are 1 1 1 2 2.

I´m still waiting for the mic to measure the crank. Slow sellers, grr!

 

Just checked everything out.

My crank is 56,985mm, each bearing is 1,990mm and the main bores are 60,990mm - with main studs fitted. So, my clearance is 0,025mm. Looks fine!

 

0.025mm is tight!!
have you thought about using HX bearings with 0.025mm extra clearance? that would bring you to 0.05mm