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Posted by: 930cabman Nov 27 2021, 09:55 AM

I recently purchased a standard size main bearing set from a large vendor, checking the clearances I am finding this new set will provide a clearance at the high limit per factory specs. My crank is spot on, but the main bearing ID appears too large. I can easily fit a .004 feeler between the crank and new bearing ID. Just for fun, I tried an old (used)main bearing and found it to have a smaller ID (by about .0015) than a new one. Am I missing something?

Thanks

Posted by: 914Sixer Nov 27 2021, 01:37 PM

You have to remember that your old bearing shell has been crushed when you put the block together. Your new bearing has not had that happen yet. Size will change after crush.

Posted by: iankarr Nov 27 2021, 04:06 PM

There's been lots of talk about quality beinig all over the place with new bearings. I had to go through two sets of Silverline before we had a workable combo. Tabari Andrade on the samba has a line on new german bearings which look promising.

Posted by: 930cabman Nov 27 2021, 04:31 PM

Does the old bearing shell remain crushed after ?? how many heat/cool cycles and years in an engine?

I was unaware of crush, thanks for informing me. I simple test would be to assemble the case/main bearings and simply measure the ID before and after installed in the case.

Silverline is the only manufacturer I have found

Posted by: 914Sixer Nov 27 2021, 07:14 PM

Yes the old bearing remains crushed. Yes you can do a before and after. If the after is not good after crush, you may have to find another set. Silverline is the only one that is steel backed. NOS German ones are rare these days.

Posted by: Mark Henry Nov 28 2021, 01:06 PM

Yes the bearings is a torqued spec. Plastigauge is about the only way to do it. I also measure the bearing shell thickness in about 5 spots to make sure the surface is even. Porsche also does this on GT3 911 bearings, you can see the mark from measuring tool.

You could get the bearings coated, but it only adds about .0002 to .0004" to the babbit surface.

Posted by: AndradeT Nov 28 2021, 09:35 PM

Thanks again Ian!

Posted by: 930cabman Nov 30 2021, 11:26 AM

Crushed!!

I may have known this in the past, but with 69 years of crap between my ears, who knows?

I did get a good measurement on the OD of a crushed main bearing and a new Silverline main bearing, about .0015 difference. Given this, the actual bearing clearance would be in the .0025 range. My next step will be to assemble the crank with new main bearings and clamp everything together in the case and see how she spins. Plastigage will work for bearing #2, but not the others.
Thanks for the replies

Posted by: 930cabman Nov 30 2021, 06:54 PM

Yes, as expected: I did assemble the crank/new main bearings with green Plasti gage in the #2 bearing. Torqued things up, took everything apart, measured between .002 and .003 with the green Plasti gage, cleaned the Plasti gage off, re assembled everything with a few drops of oil and the crank spins nice. Not super loose, but nice. Tomorrow I will take things apart again and look for and rubbing spots on the bearings. I suspect none.

Posted by: 930cabman Nov 30 2021, 06:55 PM

Yes, as expected: I did assemble the crank/new main bearings with green Plasti gage in the #2 bearing. Torqued things up, took everything apart, measured between .002 and .003 with the green Plasti gage, cleaned the Plasti gage off, re assembled everything with a few drops of oil and the crank spins nice. Not super loose, but nice. Tomorrow I will take things apart again and look for and rubbing spots on the bearings. I suspect none.

Posted by: iankarr Nov 30 2021, 11:01 PM

Is this really your first post @http://www.914world.com/bbs2/index.php?showuser=25252 ? I'm honored . You should def start a thread introducing yourself to this gang...