70 L-46 rear main bearing condition

[Dennis D.]

Pulled the cap to change the rear seal. Found this condition. Guy at the local speed shop said the flat marks are from sitting for as long time. The weight of the crank forces out the oil film enough to cause a dry start condition. Also easy to spinning the bearing. Any opinions? Should I change the bearings while I'm at it? Sounds like I'll have to drive a lot more often. (what a shame!)

[Dick W.]

Re: 70 L-46 rear main bearing condition

The bearing looks like that it also has had a lot of trash going thru it. I would change the bearings as long as I had the pan down. Depending on the mileage I might even consider an oil pump. A standard, not high pressure or volume pump

[Dennis D.]

Re: 70 L-46 rear main bearing condition

Dick

Pans off, in fact engines out for what started as a clutch R&R. Wanted to frshen up and reinstall. Your probably right to be safe than sorry. Don't know if I should search for other issues, (while-I'm-at-it). Thanks

[Joe L.]

Re: 70 L-46 rear main bearing condition

Dennis-----

This bearing may or may not suffer from any problem associated with prolonged non-use. However, it does suffer from scoring. I would replace it. Check the back side of the bearing shell and report whatever stampings that you might find on it. They will be small and, usually, lightly stamped but they should be there on either side of the bearing shell.

[Dennis D.]

Re: 70 L-46 rear main bearing condition

Joe

On one back edge: 3-92STD, LOWER, MP 2509 P

On the other back edge: CLEVITTE 77 C

[Joe R.]

Re: 70 L-46 rear main bearing condition

Dennis,

Your bearing and possibly all the bearing in you engine have been trashed. Don't know why but the bottom line is: spend a few bucks and you'll be sure that your engine is OK.

We can kick this dog to death but again the solution is change the bearings and check everything else such as the valve train.

Regards,

JR

[Dennis D.]

Re: 70 L-46 rear main bearing condition

JR

Looks like a tear down. Anything specific checking the valve train, or just in general? Thanks

[Joe R.]

Re: 70 L-46 rear main bearing condition

Dennis,

Check rocker tips, push rods, lifters and spring seats for wear and possible breakage of a spring. Also, check the timing chain for clearance to the cover. Might as well take a peek at the cam bearings. Can't be too careful.

Regards,

JR

[Joe L.]

Re: 70 L-46 rear main bearing condition

Dennis-----

The engine has had the bearings replaced previously, perhaps as part of an engine rebuild. These particular Clevite bearings were NEVER originally used in your engine. Also, these are a "tri-metal" type bearings as indicated by the "MP" code. Everyone has their own ideas about which bearings are best and some like this type. Not me, though, and for EXACTLY the reason that these bearings suffered damage-----less than ideal embedability characteristics.

Most Chevrolet engines, big block and small block, originally used premium aluminum main bearings. This is the type that I prefer for all street applications. You can obtain these from Federal Mogul and also from GM.

[Roy B.]

Re: 70 L-46 rear main bearing condition

If the crank bearing surface looks like your bearing I would do a complete engine over haul .

[Dennis D.]

Re: 70 L-46 rear main bearing condition

Joe

It's probably 10 years since a complete pro rebuild. Going to tear the engine down and inspect. Any part numbers on the bearings you suggest? Thanks

[Harold #43147]

Clevitte Tri's

I like them been using them on my OLDS race car since Christ was a Corpral Joe Mondello uses them to. Just my opinion

[Joe L.]

Re: Clevitte Tri's

Harold-----

For racing purposes, Clevite 77 tri-metal bearings are great. Federal-Mogul also makes a good tri-metal bearing for such purposes. However, for street applications, stock or hi performance, I like premium aluminum bearings best. GM has been using premium aluminum bearings pretty much across the board in Chevrolet engines, both big block and small block, for MANY years. L-88s and ZL-1s were originally built with premium aluminum bearings, too.

[Joe L.]

Re: 70 L-46 rear main bearing condition

Dennis-----

Assuming the engine stays at standard, these are the GM numbers:

mains 1-4= GM #10120990 $19.15 EACH GM list (you need 4)

rear main= GM #10120993 $39.18 EACH GM list (you need 1)

rods= GM #12523924 $27.51 EACH GM list (you need

The above-referenced parts are manufactured by Federal-Mogul. If you can find a Federal Mogul retailer that can get you the F-M premium aluminum bearings ("AP" coded) in boxed sets, you can get these a LOT cheaper. However, finding F-M premium aluminum bearings in F-M boxed sets is usually not so easy.