[Probird]

I decided to pull the engine out to fix a leak that has been getting worse all season. I pulled it twice earlier in the season thinking it was the rear pan gasket. This time I checked the rear main seal and found it to be the problem. When I pulled the rear main cap I noticed the rear most part of the bearing was down to copper. That is the only place on any of the bearings that show any amount of wear at all. Everything else looks great. What would cause this to wear to like this? Was this issue the cause of the rear main seal going bad from the heat or lack of oil?

I have lost oil pressure a few times with this engine but pulled every bearing, rods and mains (except the rear main), and they all looked perfect so I put it back together each time. These bearings have been in for 3 seasons. I don't remember when I put the rear main seal in but it's been at least 2 seasons and it might have went in when the bearings did. Was it just lack of oil when I lost oil pressure? Any ideas?

[steve25]

Well that rear main feed hole needs to be flared out to the left and right as that bearings oil hole you show in the Jurnal is restricted from what I can see!
Is this a factory block ?
How much power is the motor making?

With factory blocks at very high power levels the number 2 and 4 main bearings are most times the first to show issues due to the block flexing from not running a crank with a full 8 counter weights!

Running only a 6 counter weight Crank has has taken out many a factory block before its time once a given power level was reached.

Many times if a factory block come split down the middle and the motor was not in a detonation condition , then was due to running only a 6 counter weight Crank!

Also have you rechecked your converter for balance?

[johnta1]

Check rear crank filet.
It's probably not wide enough?
(rubbing the bearing on the edge)

[BruceWilkie]

Fillet clearance on bearing as John suggests... the following thoughts may be why.

When losing oil pressure the rear main is 1st to starve. Being wider AND the oil hole being biased to the front of the bearing... the rear part of the bearing may take longer to fully "wet" on pressure recovery.

Possibly staying "dry" on that end much longer than it took for recovery of the rest of the bearings and most of the rear bearing.

IF there is not enough oil flow escaping rearmost portion of rear bearing, the seal will not see enough oil.

A fillet issue restricting the escape path to rear could also show the bearing wear seen because the oil will take the easier escape route.

Loss of oil pressure would exasperate the situation.

Fillet issue could be bearing chamfer, radius on the crank or both.

Oil starve is a separate issue that needs to be addressed.

[Half-Inch Stud]

....just enlarged #5 & #1 uppuer Main bearing due to eclipsing feed hole.

I suggest the rear main may need the flow to float that 3rd surface. But that surface hardly has any load-share, and you load-surfaces look good.

check for Gunk in the #5 Main bearing saddles; my block had black tar gunk that no other place in the block had such. Gasoline or acetone and mechanical wipe-away.

other avenue of though is vibration or trans concentricity: check front pump bushings & converter hub for wear patterns and play. Forward pack support too. Could be easy stuff to remedy. Looksy while out.

oil pressure starve...yea

[johnta1]

BTW, Rick, was the block recently align bored/honed?

[BruceWilkie]

Originally Posted by Half-Inch Stud

....just enlarged #5 & #1 uppuer Main bearing due to eclipsing feed hole.

I suggest the rear main may need the flow to float that 3rd surface. But that surface hardly has any load-share, and you load-surfaces look good.

check for Gunk in the #5 Main bearing saddles; my block had black tar gunk that no other place in the block had such. Gasoline or acetone and mechanical wipe-away.

other avenue of though is vibration or trans concentricity: check front pump bushings & converter hub for wear patterns and play. Forward pack support too. Could be easy stuff to remedy. Looksy while out.

oil pressure starve...yea

Look at rear bearing closer...my old eyes only see wear in fillet/chamfer area at rear of that bearing..

Excessive out of round on attached convertor would put wear in more than just rearmost edge of #5.. The thrust and maybe as far forward as #1 would show something too.

[BruceWilkie]

Originally Posted by johnta1

BTW, Rick, was the block recently align bored/honed?

Bearing bore or journal tapered??? Doesn't seem as probable as your 1st instinct to look at journal fillet/ bearing chamfer as rest of bearing looks fine. Oil seal failing because of flow pinch from chamfer and journal radius seems additional clue

[johnta1]

No, I had a block align honed once where they didn't 'hone' that area of the block/cap.

They thought that little area wasn't part of the bearing surface or something?
(so they didn't run the hone all the way thru the end of block)

Measured bore and was perfect except for that small area.

It would lock up the crank though when spun over when rear cap was on though.
(how I found it)

[mgarblik]

Nothing I see from the pics indicate a cause for low oil pressure. Opening the rear feed hole in the bearing to match the hole in the block would be a good idea. I hope my next statement makes sense, but I suspect the root cause is the line hone on the block. Pontiacs have that very thin bearing area on #5 and it is difficult to hone exactly correct without care to flip the block multiple times during the hone process. When you line hone, typically the end of the block closest to the drive motor will hone a little larger than the far end. To compensate, you flip the block end-to end several times to equalize the size. It's a little tricky on that thin #5. As far as the oil leak, the seal cut groove looks very rough, even for an aftermarket block. I think you may have better luck with this particular block using a 2 piece BOP type seal so you can measure and cut the ends to get the right crush on the seal. Because of the roughness in the pic, I would put a very thin skim coat of RTV along the groove to seal the rough machining to the back of the seal. You need to do this quickly while the RTV is wet so it can flow. I know BOP does not recommend this but you appear to have a rough surface there that would be very difficult to dress. Good luck.

[Half-Inch Stud]

Bruce, I really don't know the root cause, and just trowing ideas up.

[Elarson]

Bearing #5 gets the best oil pressure and flow of all of them, if the feed hole isn't restricted. I'm in the same camp, believing it's a dimensional problem with the crank fillet or line hone.

Eric

[Probird]

Originally Posted by steve25

Well that rear main feed hole needs to be flared out to the left and right as that bearings oil hole you show in the Jurnal is restricted from what I can see!
Is this a factory block ?
How much power is the motor making?

With factory blocks at very high power levels the number 2 and 4 main bearings are most times the first to show issues due to the block flexing from not running a crank with a full 8 counter weights!

Running only a 6 counter weight Crank has has taken out many a factory block before its time once a given power level was reached.

Many times if a factory block come split down the middle and the motor was not in a detonation condition , then was due to running only a 6 counter weight Crank!

Also have you rechecked your converter for balance?

This an IA2 block making about 800hp or so.

Originally Posted by johnta1

Check rear crank filet.
It's probably not wide enough?
(rubbing the bearing on the edge)

That was my first thought too. I laid the bearing on the crank and it didn't look to be riding on the filet area. But it could be.

Originally Posted by johnta1

BTW, Rick, was the block recently align bored/honed?

Not recently. It was done about 5 years ago. I just went down and looked at the previous set of bearings that was in there for 2 years and it doesn't show this issue. This is also the same crankshaft.

Originally Posted by mgarblik

Nothing I see from the pics indicate a cause for low oil pressure. Opening the rear feed hole in the bearing to match the hole in the block would be a good idea. I hope my next statement makes sense, but I suspect the root cause is the line hone on the block. Pontiacs have that very thin bearing area on #5 and it is difficult to hone exactly correct without care to flip the block multiple times during the hone process. When you line hone, typically the end of the block closest to the drive motor will hone a little larger than the far end. To compensate, you flip the block end-to end several times to equalize the size. It's a little tricky on that thin #5. As far as the oil leak, the seal cut groove looks very rough, even for an aftermarket block. I think you may have better luck with this particular block using a 2 piece BOP type seal so you can measure and cut the ends to get the right crush on the seal. Because of the roughness in the pic, I would put a very thin skim coat of RTV along the groove to seal the rough machining to the back of the seal. You need to do this quickly while the RTV is wet so it can flow. I know BOP does not recommend this but you appear to have a rough surface there that would be very difficult to dress. Good luck.

I did previously run the 2 piece BOP seal and didn't have this problem. I bought another one piece to replace this one last week before I found this thinking it might be the problem since replacing the pan gasket twice didn't fix the leak. I'll try the RTV thing and see how it goes.

Originally Posted by Elarson

Bearing #5 gets the best oil pressure and flow of all of them, if the feed hole isn't restricted. I'm in the same camp, believing it's a dimensional problem with the crank fillet or line hone.

Eric

See the pic of the old bearing that was in there for 2 seasons, roughly 300 passes. No work done to the block or crank since this one was in there. The worn bearing was in for maybe another 150 passes more than the old one. Maybe a bearing dimension issue?

We only have 5 or so more weekends left to race so I'll be pulling it out again then to see if the RTV trick worked. I'll also put the old undamaged rear main bearing back in and see what it looks like. I'll probably only put 40 or so more passes on it though.

[Half-Inch Stud]

Could say that copper-tracked bearing is as right as rain now. Some 600 grit on the copper rail and.....

MAYBE the Rear Main Cap was cocked with sealant, to cause the bearing shells to cock under crush, to cause that wear. Whereas the Lower shell front load-bear surface has an oil float to avoid such a wear pattern. We're talking a mil or two to show such copper.

[charlie66]

I would put the old bearing back in the cap/block , torque it down with out the crank and measure it front and back to see if its the same . Measure the crank as well and compare and see what your clearances are. It might of been a bad bearing is all ... or too close to the radius...

Good luck im sure you will work it out....

[chiefbigb]

What does the imprint on the back side of the bearing look like?

[Tiger Paw]

The aftermarket crank that I bought had all the mains slightly hourglass shaped journals, so that would be my guess. I would modify that oil hole to match the bearing.

[chiefbigb]

On the mains if I'm concerned of a radius problem I will remove the thrust bearing and measure crankshaft end play then install it. If im well within the measurements taken prior I'm good. Just how I check this. I have had this same problem it was in the housing bore.

[Half-Inch Stud]

Originally Posted by chiefbigb

What does the imprint on the back side of the bearing look like?

Yea,Ditto.

Can you flip BOTH shells over a post the photo?

[Probird]

Originally Posted by Half-Inch Stud

Yea,Ditto.

Can you flip BOTH shells over a post the photo?

Here is a pic of the back of both shells. In the other pic I'm pointing at one of the slots in the main cap. That one was almost completely covered with silicone. Will that cause an issue?