Crank Regrind

[1972_911T]

When A crank is reground is it common practice to to regrind both mains and big end journals to the same ie both 0.25 not one 0.25 and the other 0.5?

I Ask because ive just picked up a 77 CIS core engine that ive bought for my RS engine project the previous owner knows nothing of this engine except he got it with aload of spares when he bought his 71 911. Its clear to see the crank has been very recently reground and new bearing are fitted however the main bearings are showing alot of wear in the centre but none at the edge. The mains are 0.25's but the big end bearings are 0.5's is it likely the previous builder has fitted the wrong bearings? probably the cause of it been scraped shortly after a recent build?

I know the answer is to measure the journals but I just dont have anything to measure with here at the minute.

Steve

Pic to follow when my cam is charged

[1972_911T]

Some pics



Steve

[afterburn 549]

As I understand the problem anything can be done, but with a P crank you are better off to buy a good used one....I could go into all the suposed reasons ...but thats what I think I know

[89turbocabmike]

Steve, it's common to have different size mains/rods. No sense re-grinding further than you need to as the o/s bearings just go up in price with each oversize, especially mains. Re: bearing wear it's always tough to know on a used motor that you never hear running, especially those mag 2.7's. I've had my share of bad luck with used 2.7's. I took apart a used "recently rebuilt" motor that obviously was run for along time with rod and main bearing knock. The rods had clearance of about 1/4 inch and the main bearing shells were worn down almost to the saddle, so I would take little for granted on a motor in which you are at least the 2nd non-running owner of Measuring will be necessary, but that wear could easily be from lots of miles with poor lubrication/oil.

[chris_seven]

Steve,

It relly is important to measure the crank properly to make sure it has been gound correctly and that the radii are correct.

Do you know if the crank has been re-heat treated and bungs replaced after cleaning?

[1972_911T]

Hi Chris

I know nothing of this crank it just came with a bunch of 2.7 parts I bought, i was only going on what bearings were fitted to it. My plans have however now changed and I wont be using it.

Thanks Steve