[Ken K]

I am going to have a Pontiac 400 crankshaft reground .010 -.010, I need to know if it is a good idea to have the crankshaft ground .012-.012 instead for a little more clearance. I was told it was better to have the crank ground on the low side because the crank will spin easier and there would be less of a break in. Is this a good idea for a Pontiac crank or should I just have it cut .010-.010?

[Ken K]

I am going to have a Pontiac 400 crankshaft reground .010 -.010, I need to know if it is a good idea to have the crankshaft ground .012-.012 instead for a little more clearance. I was told it was better to have the crank ground on the low side because the crank will spin easier and there would be less of a break in. Is this a good idea for a Pontiac crank or should I just have it cut .010-.010?

[Old Man Taylor]

Either leave it 10-10, or mike the bearings in the rods and grind the crank to a specific clearance. DO NOT grind it 12-12. For a nice street engine I like mine just under 0.002. For my racecar I had it ground to 0.00225. I was being picky.

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Jim

[Will]

I second Jim. Without measuring the bearings as installed in the block or rods, you really don't know what clearances you're going to end up with. .002" is a BIG difference and could make the difference between an engine that has good oil pressure and one that doesn't.

With today's oils, it's actually a good idea to keep clearances tighter than in "the old days." Main clearances of .002-.0025" are perfect for a high-performance application, rod clearances of .002" should be just fine also.

Keeping the clearances at these specs allows you to run a lighter oil for better power production while still keeping good oil pressure.

[Ken K]

Thanks, you guys saved me a world of grief on a Pontiac crank. I wish I was as lucky on a small block Chevy crank I already had turned, I have the cranks turned in Mexico and they come back slicker than snot but I have someone else take them over for me and the guy that brings them over took it upon himself to have the Chevy crank cut on the low side. I will use plasti gauge to see what the clearances are. It's a good thing I know someone with every type of Chevy engine part known to man in his garage, I went over an discussed the crank with him and he said when you have the crank cut you want it dead on. He had a high volume pump, he said he does not like to use a high volume pump because it mask other problems if something goes wrong. I am not worried to much about the Chevy because they cost nothing to build. He also mentioned that Sprint cars run a .015 clearance on the rods and mains and they use a super high volume oil pump and the rods and cranks run on a cushion of oil but those engines are not made to last long.