Rear main bearing wear

apbright

apbright

Senior Member
While giving the engine a minor revamp, I inspected the condition of the crankshaft bearings. The lower rear main bearing showed some wear, pictured.

Would an engine-person say this is normal wear after 8000 miles, or the sign of something wrong?
 

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Where does that extra hole in the babbit oil groove lead?

I hope it's from a pressure feed line and not an extra drain hole.
From the looks of the babbit, I'd bet it's a drain hole.

Do a search for pictures of babbit by Herm, and you will see how it should look.
 
Guys I believe I see the bearing tang in the normal place and thrust bearing is no doubt there somewhere safe as the recess has been machined
About the original question I have seen this wear pattern when the rear seal sits a thou or 2 proud if you finish the seal flat with the block the bearing cap will sit flat
check the crank and the tunnel also for taper with a good micrometer I bet you will find the seal sits high
 
I can now see the bearing was originally designed for another engine, and the oil hole is blocked by the cap. It does look like the oil wasn't changed as often as it should have been, or maybe the engine wasn't totally clean when it was assembled. I'd plastigauge the bearings, and if they are good, I'd probably put it together and run it also. It would depend on how the crankshaft looks.

Why was it taken apart?
 
Is the wear pattern the same on the other bearing half? Sometimes a piece of debris can get between the bearing she'll and the block an cause that kind of wear. See if something is embedded in the back side of the shell.
 
colin1928 said:
Guys I believe I see the bearing tang in the normal place and thrust bearing is no doubt there somewhere safe as the recess has been machined
About the original question I have seen this wear pattern when the rear seal sits a thou or 2 proud if you finish the seal flat with the block the bearing cap will sit flat
check the crank and the tunnel also for taper with a good micrometer I bet you will find the seal sits high
Click to expand...

Hey colin,
Well, I have some 99 cent drug store glasses that tell me that I see tangs too, but I don't believe it :eek: !
If it isn't driven with much rpm and high speed...what's it matter , eh...stick it back together :)
 
It's hard to see in picture, but it looks like the results of debris in the oil, further back you can see specks of debris embedded, when there are a lot of debris the babbitt is raised due to the debris and gets smeared----continued running with debris loaded bearing material will wear the crankshaft even if the clearances are good
they look like AER inserts
 
Kurt in NJ said:
It's hard to see in picture, but it looks like the results of debris in the oil, further back you can see specks of debris embedded, when there are a lot of debris the babbitt is raised due to the debris and gets smeared----continued running with debris loaded bearing material will wear the crankshaft even if the clearances are good
they look like AER inserts
Click to expand...

I am almost positive these bearings are early AER inserts. The bearing material was originally Babbitt over steel. Later production had aluminum over steel for the bearing surface. Vince makes mention of the bearing tang is missing but I think I see a bit of the tang hidden in the dark area below the radial oil groove.

The engine was likely built with a 1/2 rear thrust. When AER brought these bearings to market, he was only installing a 1/2 thrust washer and it was attached to the block. The front thrust is inset into the block, so since we only see photos of the cap, we are not seeing the thrusts. The front thrust is not dowelled like the rear, it is captured and held from spinning by the cap. AER is now installing a full rear thrust by using two 1/2 circle thrust washer.

If this engine were mine, I would order a replacement set of aluminum lined AER bearings and keep these for the shelf to look at.

I just went back and looked at the bearings again and I am now convinced these are an early production AER bearing. The oil wells at the parting line in the later bearings is run closer to the rear of the bearing.
Good Day!
 
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i'd be putting new bearings in if it was me they don't cost that much compared to the alternative
Terry n
 
It is machined for the rear thrust. I can see the counter bore. For the price of the bearings I would change them. But I would also check the crank and check for end play.
 
Hi chaps,

Thanks for all of the comments.

These are AER insert bearings, 30/1000th's oversized. Roughly speaking, the upper half of the rear main bearing looked slightly better than the lower (pictured) bearing, but not perfect.

I took the engine apart due to oil leaks. My primary suspect for the leaks was a poorly-sealing oil pan gasket, but I decided to check the bearings while I had the engine out.

I have been changing the oil about every 2000-3000 miles. I have a full-flow oil filter, in case that matters.

I have a replacement-set of insert bearings, with which I intend to replace these bearings. I'm travelling on business right now, will post additional pictures when I return home.

Thanks all, Andrew
 
Returning to this topic, I had also found that the rear main seal had partially disintegrated (see photo); a new rear main seal has been replaced. I also replaced the main insert bearings with a new 030-oversied set ordered from Snyder's (though they do say 'AER' on them).

The engine was re-assembled and a new oil-pan gasket applied with RTV sealant. I have now had about 550 miles on it; it does not leak a drop of oil - a first for me and this car, so mission accomplished.

To answer Tom Wesenberg's question: The thrust bearings were indeed in the engine; I had removed them (they fell out, to be precise) before taking the first picture.
 

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