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Old 10-14-2010, 05:10 AM
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Bearing Wear Pics - what story do they tell?

I was sorting out some trash and came across bearings discarded after my last 428 rebuild.

Here's a pic of two main bearing halves that both show copper from wear. One is obviously #3 and appears to be the bottom half based on rotation marks on thrust face and bearing tang orientation. The other is the rear bearing, #5. I'm not sure wether it's a top or bottom half any more. All other main bearings (and the other half of the ones shown) look fine, and all rod bearings look fine.....well, rod bearings had no wear....there were some minor longitudinal chatter marks from detonation.

These bearings had only 3000 miles on them and came out of an engine that had a piston break due to detonation. There was some scratching from debris.

The crank had been bought already ground, but my machine shop found taper on the journals and reground it. It was also checked for straightness. A reputable place and I know the owner.

So I'm wondering what caused the odd wear pattern. Some things come to mind:

1/ too many cold start-ups

2/ low oil pressure

3/ crank bent or journal taper

4/ misalaigned bellhousing

Any thoughts?


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Old 10-14-2010, 07:49 AM
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2 things, align honing, and crank flex under power.With 5 and 3 I would check the alignment of the mains. New crank + old main caps and block = premature bearing wear. Some people think that just a new crank and bearings is all that's needed and in some cases, it's not. Aling honing is sort of like insurance in case is does. After install, priming the engine is just as important to the rod and main bearings as it is to the cam and lifters.

One other thing might be oil starvation on hard cornering with low oil level.
the first bearings to feel the pressure lost would be the ones closest to the oil pump until the car straightens up and the pump re-primes. A distinct whirring sound from the bearings running dry can be heard like a kid trying to whistle with his two front teeth missing.

Last edited by sqzbox; 10-14-2010 at 08:01 AM.
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Old 10-14-2010, 07:58 AM
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Thanks for the reply. I did have the block align honed, or at least it was on my list and they charged me for it.....LOL. Crank flex......it's a pretty stout crank, but is turned 0.040" under. And I forgot until now, but I did over-rev the crap out of it once.....shifted to 3rd and noticed i was getting handy to 80 mph.

I's running a baffled 9 qt oil pan, and havn't cornered all that hard. But with braking and accelerating, it could have happened.

Oil feed starts in the front, with the rear main getting the least amount of oil. Back two rods were fine. It seems to be something mechanically out of whack vs lack of oil.

I find it inteersting the wear is only on one side of the bearing shell, and on the other halves (not shown), they look fine.
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Old 10-14-2010, 08:05 AM
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Did you do anything different when you rebuilt the engine? And how many miles since?
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Old 10-14-2010, 08:19 AM
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No, I didn't, other than reboring for a new set of pistons. It's been about 500 miles since the last rebuild. I am planning on removing the oil pan to check things sometime this fall or over the winter.
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Old 10-14-2010, 08:22 AM
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Most times a grooved bearing insert will be the upper half (due to the oil feed hole), unless they're a full grooved set, that was done w/both "upper" halves.

A better "read" could be made if all the bearings were in order so as to see the entire picture, but from what little can be seen here, I'd hazard a guess that the crank was not straight, the saddles were out of alignment or the crank had a tapered journal.

Are these bearings from before the crank was reground (hopefully )?
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Old 10-14-2010, 08:34 AM
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Did you clean the crank after it came back from the grinder or manufacturer. Your bearings show some material imbedding in addition to a probable short term loss of oil pressure.

Even if you are buying a brand new crank from a hi end manufacturer or OEM, you have to run rifle brushes thru the crank and motor to get an leftover machining grub thats been left behind.

Your machinist may or may not do this, dont take a chance.
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Old 10-14-2010, 08:41 AM
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Quote:
Originally Posted by cobalt327
Most times a grooved bearing insert will be the upper half (due to the oil feed hole), unless they're a full grooved set, that was done w/both "upper" halves.

A better "read" could be made if all the bearings were in order so as to see the entire picture, but from what little can be seen here, I'd hazard a guess that the crank was not straight, the saddles were out of alignment or the crank had a tapered journal.

Are these bearings from before the crank was reground (hopefully )?
They were Clevite 77 bearings and all were fully grooved with oiling holes in both halves. Next time I think I'll try to get 3/4 groove bearings.

No...it was the time before the crank was ground. You know, now that I think about it, when I checked the clearance with Plastiguage, I seem to remember one side of the plastigauge being wider than the other. I think I chalked that up to thinking I had assebled things a little crooked, as it was sort of a quickie check....not done as carefully as when I do the final assembly.

I really didnt' think too much about this when I did the engine. Silly me. I have been cleaning up my garage lately, and found the old bearings. So I don't know which ones went where any more other than I remember those ones showing copper.

I guess all I can do is check them again when I drop the pan. I doubt I'll check #5 unless I have to as installing the rear cap with seal is a pain in the butt when you work under the car. If #3 is bad again, then I'll check #5 as the engine may come out on account of this.
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Old 10-14-2010, 08:49 AM
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I can appreciate your concern AND your thoroughness in investigating both the cause of the bearing wear in the first place and the aftermath of the machinist's work- a lot of guys would just assume things are hunky dory and not go looking for trouble. At this juncture, I believe the bearings will be fine- but far better to know FOR SURE rather than taking it on faith.

Good luck.
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Old 10-14-2010, 08:50 AM
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Quote:
Originally Posted by FmrStrtracer
Did you clean the crank after it came back from the grinder or manufacturer. Your bearings show some material imbedding in addition to a probable short term loss of oil pressure.

Even if you are buying a brand new crank from a hi end manufacturer or OEM, you have to run rifle brushes thru the crank and motor to get an leftover machining grub thats been left behind.

Your machinist may or may not do this, dont take a chance.
I usually just push a bit of wadded up paper towel through the crank oil holes a few times. Then I blow compressed air through it. I may or may not have done it during that rebuild as it was quite a few years ago and I don't remember. Chances are I did do it, but I've made mistakes before.
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Old 10-14-2010, 08:55 AM
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Quote:
Originally Posted by cobalt327
I can appreciate your concern AND your thoroughness in investigating both the cause of the bearing wear in the first place and the aftermath of the machinist's work- a lot of guys would just assume things are hunky dory and not go looking for trouble. At this juncture, I believe the bearings will be fine- but far better to know FOR SURE rather than taking it on faith.

Good luck.
LOL.....I'm going to take that as a compliment, but the fact is, I should have done more checking when I saw those worn bearings. So if you're being facetious, that's OK......I did slip up.
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Old 10-14-2010, 09:08 AM
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Not jazzing ya', straight up.
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Old 10-14-2010, 09:15 AM
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Was the piston that went to pieces connected to the rod bearing in question?
And were any of the other pistons having any issues or were they all good?
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Old 10-14-2010, 09:23 AM
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Quote:
Originally Posted by cobalt327
Not jazzing ya', straight up.
Thank-you. I do try.

Quote:
Originally Posted by sqzbox
Was the piston that went to pieces connected to the rod bearing in question?
And were any of the other pistons having any issues or were they all good?
The bearings shown were main bearings. All the rod bearings looked fine, except a few had some light lines across them which I suspect happened due to the rods being hammered.

Detonation was limited to the right back. #1 broke, some signs of detonation on #2, less on #3, #4 was fine. Not sure why the left bank (5 thru 8) were OK. The front to back issue makes sense as the combustion chambers run hottest near the front of the engine. The coolant goes from the front of the block to the rear, then up to the heads, and back through the heads to the front of the engine, picking up heat all the way along.
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Old 10-14-2010, 09:36 AM
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It's not unusual for the deck height to differ from one bank to the other. But if your block was checked/corrected, this wouldn't be the problem.

Another possibility is the crankshaft journal indexing. If it's off, you can have some amount of "advance" ground into the journals. Same thing w/the camshaft, but the effect wouldn't be as pronounced as far as detonation goes, though, and that would have been discovered during the cam degreeing phase of the build.
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