This is main bearing from my friends engine. Something is wrong, but what? It has some brown colour and little spots in it, and in some areas the tin surface has been flaking off. Clearances are fine, .0025" rods and .003" mains.

Could too hot oil, or some kind of oil pump cavitation problem cause this? My friend doesn´t run oil temp gauge, but oil pressure has been dropping in some cases, like in highway with engine running 5000 rpms, indicating that oil is getting too hot. He does run B&M 5 x 11" oil cooler. It´s a sbc engine with hv oilpump in it, and he has been told that the hv pump is causing a cavitation problem, and that he needs smaller volume pump with some kind of anti-cavitation grooves. Does this sound right to you?

I saw something similar on a mains bearing in my old 528. Looked like the surface was de-laminating, had a sort of crazing effect to it. Happened on only one half of the bearing as well. Never figured out why, just put it down to a manufacturing fault. Didn't mark the crank either. Cant remember any disclouration though
Are all the bearings like this? in our case it was just one shell.

with the pics you posted I would say It looks like there is/was some detnation going on!

Look at how much of the oil groove in that bearing is either filled with bearing material or worn away. Oil starvation would be my first guess. What do the rest of the bearing upper and lower shells look like??? How about the rod bearings??

From THAT picture ( its VERY hard to read a bearing from a picture) but I would say you have bearing fatigue or whats called surface fatigue. Ity doesnt appear to be 100% cavitation or lack of oil to me. That is what most people want to say is lack of oil, but there are many factors that go into reading bearings, and they are like spark plugs, most read them wrong.


Fatigue can be ( as mentioned) detonation, overloading, ( which can be lugging the motor, detonation and overfueling, rich condition thinning oil). It could also simply be a bad bearing choice for the application.

You would want to really take a good look at the distributor and timing, make sure the oil pick up is in good shape and sealed well, there is proper clearance pan/pickup and make sure its not overly rich.

With all that being said, it does appear that there could be some surface wiping, which would indicate some starvation, but it usually doesnt show the signs of the distressed plating ( the wrought peppering look) that your bearing is showing. Without knowing all the exact details of the bearings, clearances, how it was assembled, primed properly etc, as well as the visual first hand observation of the bearings, its educated analysis from our chairs.

Again, I still believe bearing fatigue from what I see.

My

If you can take a couple more pics, 1 to get the
glare off of it and take a pic of the thickness of
the bearing(side view) to see how much wear it has.
It looks like the oil groove is full of material
or it could be worn away. But looking at the end
of the bearing it would show a different material
if it was worn that thin

Yes its just hard to tell. The bearing filling up could be after the initial damage was done which may or may not be the reral problem, only a result of. Just so hard to tell from pics.

The way the groove seems to taper I would have to belive that is not a full groove bearing.

The groove isn´t filled, it´s a 3/4 groove bearing, and theres really nothing wrong with the groove. No surface wiping either, only the thin tin layer has been flaking. So I don´t think it´s oil starvation. Detonation shoudn´t be a problem either, it´s a quench motor with 8.1 dynamic CR.

We thought the problem is oil temp related because this engine has been ruining the oil very fast. After about 600 street miles the oil looks really bad and it has lost most of its viscosity. Oil used is valvoline VR1 20W/50. Oil pressure drops to 55 psi from normal 65 psi when driving in highway at 5000 rpms for about 10-20 miles, so the oil is probably running very hot.

Theory about the HV oil pump is, if I have unerstood it right, that it´s producing more oil at higher rpms that the engine can take and basicly cooking up the oil. Cavitation probably isn´t the right term. Pressure relief valve is circulating the oil back to suction side, so it most likely just creates more heat as the oil is circulating very fast around the pump.

Another pic.

One more.

can you post a picture of the mating shell. my guess is it doesn't look as bad as the one you already posted. if that's the case, detonation, overloading would be the likely culprits.

Detonation shoudn´t be a problem either, it´s a quench motor with 8.1 dynamic CR.

Pressure relief valve is circulating the oil back to suction side, so it most likely just creates more heat as the oil is circulating very fast around the pump.

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With the detonation, you are right 8.1 should not cause detonation, but other factors could cause even and 8.1 motor to detonate (something glowing hot in the combustion chamber, bad fuel, timing, lack of mixture swirl, a combination of the above, etc.) I guess you would need to look at all the evidence to rule this out (pistons, plugs, rod bearing, etc)

As far as the pump, others can correct me if I am wrong, but my understanding is that Mopars have a very efficient pressure relief system where the oil does not get dumped directly to the sump (I believe Chebby does this). On Mopars, as you said, the oil swirls around the rotors which taxes the suction side less which in turn results in cooler oil (like I said, I could be wrong on this as I'm going by memory).

while your at it, how about a picture of the back of the bearing shells? (both)

This is a sb chebby engine we are talking about. Sorry for posting here, but I don´t hang out in chebby forums, and I also didn´t thought that we need a chevy guy to read a bearing

Back to the issue. Rod bearings were looking better, only a little brown colour and spots, but no flaking. Mains were all looking like the one in the pic. If it was a detonation issue, shoudn´t the rod bearings be worse.

To me it looks like the bearings have just been running too hot, and the tin surface has been baked. And if so, we should figure out why. The guy who was thinking that HV oil pump is cooking the oil is actually a race parts dealer, and he claims that a pump with anti-cavitation grooves and only 10% more volume (instead od of 25%) will cure the problem.

please post good clear pictures of the front and back of a pair of rod bearings and main bearings.
it's hard to tell what the problem is when it's only being described by someone. pictures ar worth 1000 words.