Main bearing pitting

[DougsfastZ]

Took out my rear main cap last night to do the rear main seal, and saw some slight pitting in the bearing. The crank looked fine, but wanted to know if I need to replace the bearing or check the other ones.

Here are some pics. Let me know what you all think.

http://www.zmydust.com/dougsfastz/images/GN/IMG_3819.JPG
http://www.zmydust.com/dougsfastz/images/GN/IMG_3820.JPG

In the second pic, you can see it on the left side.

Doug D

 

[QuickWrench]

It looks like dirt, or some other physical contaminant. Was a head gasket ever blown in this motor? These look like OE bearings, how many miles were on the motor?

Grab new ones, and keep the oil changed.

 

[DougsfastZ]

Don't know of a head gasket ever blown. The motor has 83k miles.

Doug D

 

[QuickWrench]

The originals took the beating, just like they were supposed to. Since the crank looks fine, grab a new set of bearings...and you're probably good to go.

Although this may draw some flaming, see if you can find some Plastiguage for when you fit the new ones, just to make sure of the clearance. No, it's not like using mic's; but with the crank still in the engine, your options are pretty limited. I've seen whole sets of Clevites come out of the box wrong, so at least you'll have some peace of mind before you turn the key.

If you do use it, make SURE to scrape off the plastic before the final retorque, and use some assembly lube on the journals. Double-check those rod bearings, too.

Good luck.

 

[Red Regal T]

OK.......I'll flame ya......... if the bearings are original standard, just replace them, with standard MS960P in clevite 77. No need to measure anything. There's nothing you can do. You won't have a problem. You might as well replace them. It'll just take a couple hours. I just did my GN about 6 months ago, and they looked like that. I'm not sure waht the oil pressure was because I had an electric gauge. I went in to replace the rear seal, and decided to replace all the bearing while there. I've installed a mechanical gauge and have 30 PSI at hot idle and over 55 at 2000 RPM hot cruise.

 

[CTX-SLPR]

I'll flame back, I had a 65 Riviera GS that had a motor that was just rebuilt because it had been sitting for awhile so they went through and replaces the seals, gaskets and bearings but the factory had installed an oversized bearing on one of the journals so when I changed the oil from the thick stuff to synthetic 10W30, I got a bearing knock..... Always check the clearances.

 

[Red Regal T]

Originally posted by CTX-SLPR
I'll flame back, I had a 65 Riviera GS that had a motor that was just rebuilt because it had been sitting for awhile so they went through and replaces the seals, gaskets and bearings but the factory had installed an oversized bearing on one of the journals so when I changed the oil from the thick stuff to synthetic 10W30, I got a bearing knock..... Always check the clearances.

APPLES AND ORANGES.

Do you have anymore to add to the story that's different than this situation? A 65 motor rebuilt for how many miles?........by who knows who, somebody who didn't do a good job...........wasn't the motor out? This one isn't.

APPLES AND ORANGES

 

[DougsfastZ]

What bearings should I get and from where?

Oil pressure was 22-25 psi at idle on a hot summer day before I tore it down.

Thanks,

Doug D

 

[Red Regal T]

Well, that's pretty good. Maybe you should just put that bearing back in and button it up. I just thought maybe, since you were there you could re-new but, doesn't sound like it's necessary. That's up to you........you know your car.

Clevite 77.. MS960P is the Clevite #.

 

[CTX-SLPR]

Yes motor was out of the car, but the car only had about 86k miles on it at the time. It had just been sitting there for 10 years in a carport in Chicago so rather than risk corrored stuff they just swapped the bearings, no machine work as the crank was still good. It was only the #4 main bearing that knocked, when I had it looked at before I sold it the mechanic said it was an oversized bearing on a factory undersized journal as all the rest were standard. Crank had not been turned, nailheads have forged internals, just new bearings thoughout.
If you want to risk it... go ahead, its easy enough to do plastigauge that I'd use it for cheap insurance because if you can get the bolts and/or studs out to take the maincaps off you can certainaly get some of that stuff in there and check it. I'm going to check mine when I build mine and the machine shop already did it and I trust "Ohio" George Montgomery more than just about anyone else with building a Buick V6.

 

[miked]

Bearing replacement

I agree with Red-Regal, just change the bearings. I also had the same problem, just change the bearings,put a new oil pump pick-up. THe car has run great! Just my opinion, Thanks Mike D.

 

[65vette396]

Originally posted by Red Regal T
APPLES AND ORANGES.

Do you have anymore to add to the story that's different than this situation? A 65 motor rebuilt for how many miles?........by who knows who, somebody who didn't do a good job...........wasn't the motor out? This one isn't.

APPLES AND ORANGES

I'm not trying to argue with you or prove you wrong. But I agree with QuickWrench. I always use plasti gauge if I can not mic the clearances. I had a problem with a brand new set of bearings once and it was worse than the whole set being messed up. I had a big block chevy I was freshining up and the crank was .010 under. 6 or the rod bearings were .010" under. One was standard, and one was for a .020" under crank. I have since never had a problem with a clevite or any other brand of bearing. But it's enough to make sure you check and double check from now on. Drew

 

[turbofish38]

My understanding is that Buick and GM did use OVERsize bearings to assemble the motors as evidenced by all of the odd ball part numbers in the engine assembly manuals used at the factories. Unfortunetly all anybody makes is standard and UNDERsize bearings so like Red says, go with standards. You can tell if they are GM bearings as a lot of times the size and numbers are still printed on the out side of the bearing shell. Sometimes the numbers imprint themselves on the rods and main caps. Excuse me if you think I have the word over and under backwards. This is the terminolgy used in the shop manuals.

 

[Red Regal T]

Originally posted by 65vette396
I'm not trying to argue with you or prove you wrong. But I agree with QuickWrench. I always use plasti gauge if I can not mic the clearances. I had a problem with a brand new set of bearings once and it was worse than the whole set being messed up. I had a big block chevy I was freshining up and the crank was .010 under. 6 or the rod bearings were .010" under. One was standard, and one was for a .020" under crank. I have since never had a problem with a clevite or any other brand of bearing. But it's enough to make sure you check and double check from now on. Drew

Probably because your talking about BRAND X.

 

[CTX-SLPR]

and you are saying that Brand X's assembly lines are shoddy compared to Buicks......? Same freak'n company man!! I always check the bearing clearances, especially with our cast cranks, an undersized journal that hammers the bearing would ruin your day really fast and force you to cut a perfectly good crank. Better safe than sorry, now if you will excuse me I'm going to go grab some plastigauge so I can check my main bearing clearances on my 4.1 that just came home from the shop.

 

[65vette396]

Originally posted by Red Regal T
Probably because your talking about BRAND X.

If you call Clevite brand X, you are correct

 

[Red Regal T]

Originally posted by CTX-SLPR
and you are saying that Brand X's assembly lines are shoddy compared to Buicks......? Same freak'n company man!! I always check the bearing clearances, especially with our cast cranks, an undersized journal that hammers the bearing would ruin your day really fast and force you to cut a perfectly good crank. Better safe than sorry, now if you will excuse me I'm going to go grab some plastigauge so I can check my main bearing clearances on my 4.1 that just came home from the shop.

Well, chevy's do suck, but that's another matter. Why do you keep talking about your motors that are on a stand, out of the car? The thread was about an "in" car situation. While you lay on your back, under the car, you roll the bearing out..........the old bearings are marked. If standard, replace with standard.

Now, if your new motor is on an engine stand in front of you, of course, I would recommend at least checking clearances with plastigauge. OK?