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Old 06-27-2010, 11:02 AM   #1
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Default Problem with ACL race rod bearings?

I am seeing about .002" out-of-round with these ACL race bearings. I have brand new CompStar rods, which measured 2.2501 on the bore gage with less than .0001" out-of-round. On the rod centerline I measured about .0031" clearance. When I rotated the bore gage around to the bearing split line, the clearance grows to about .005". All 8 bearings measured very similar within a couple of tenths...

Sounds normal after responses from engine builders.
Thanks guys.

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Old 06-27-2010, 11:17 AM   #2
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I am seeing about .002" out-of-round with these ACL race bearings. I have brand new CompStar rods, which measured 2.2501 on the bore gage with less than .0001" out-of-round. On the rod centerline I measured about .0031" clearance. When I rotated the bore gage around to the bearing split line, the clearance grows to about .005". All 8 bearings measured very similar within a couple of tenths...

Is this normal for these bearings or are these ACL bearings junk? Any suggestions?
Thanks

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all bearings are out of round-this promotes the hydrodynamic wedge.
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Old 06-27-2010, 11:35 AM   #3
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What is a general out-of-round spec for rod bearings then?
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Old 06-27-2010, 06:16 PM   #4
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Default Eccentricity

The out of round spec. of .002" is average for most race style bearings. Not enough eccentricity and the bearing will pinch the crank at high revs due to distortion of the con rod big end.

I don't know what you are building there but three thou is a bit much for vertical clearance regardless.
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Old 06-27-2010, 07:40 PM   #5
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The out of round spec. of .002" is average for most race style bearings. Not enough eccentricity and the bearing will pinch the crank at high revs due to distortion of the con rod big end.

I don't know what you are building there but three thou is a bit much for vertical clearance regardless.
Thanks! That's exactly what I am looking for.

My build is a Turbo 408 est 1000FWHP. Not sure if I can really hit that number, but it should be close. I was going to shoot for .0025-.0030 for all rods and mains. I am about a tenth bigger than I was expecting, but I'm not sure if I should buy another set of bearings.
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Old 06-28-2010, 07:23 PM   #6
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Those are normal rod bearings for medium eccentricity or "H" style just to get you even one more vote of confidence.
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Old 06-28-2010, 08:22 PM   #7
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Those are normal rod bearings for medium eccentricity or "H" style just to get you even one more vote of confidence.
Thanks Erik!

Am I correct to assume that the main bearings will not have this eccentricity built into the bearing (or not as much) since the cap and block are so stout and should not see much close in?

BTW I got my Trick Flow heads in today you sent and they look nice! Thanks for all of your work switching the AFR for these. I will definitely be buying more from you in the future.
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Old 06-28-2010, 09:25 PM   #8
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The mains also do have some eccentricity as well. The OEMs have very little but all the race style bearings do. It's just how they are made.
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Old 06-29-2010, 12:48 PM   #9
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Am I correct to assume that the main bearings will not have this eccentricity built into the bearing (or not as much) since the cap and block are so stout and should not see much close in?
Like Shawn said, you need the out-of-round area to build a hydrodynamic wedge of oil between the journal and bearing. It's the same reason the thrust bearing suface has those little troughs on them. Clevite has a nice bit of info on this in their catalog, which you can even find online.
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Old 06-29-2010, 12:48 PM
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002, acl, avl, bearing, bearings, connecting, eccentricity, ls2, ls7, lsx, main, mustang, problems, race, review, rod


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