Crank Bearing Damage

[inthegarage]

Hello, I've been in the process of replacing gaskets/seals to a 1980 GM 151 in my CJ7 .

I dropped the pan yesterday and found a large broken bolt laying there. It came from the 2nd main bearing cap. I don't know how long it has been there, the engine was running/driving before I tore it down. It made a good bit of noise when it did run, but kind of what I expected from a nearly 40 year old Iron Duke.

I removed the cap today and looked at the bearing. I'm not sure if it is ok, this is my first work inside an engine. So I'm looking for help on if this bearing and crankshaft needs significant work after running without a bolt in one of the mains.

Thanks!

 

[gert]

It doesn’t look like it has spun, its old and worn but not worn out.....


Go to the parts store and get some plastigage and take a reading of the bearing clearance, if the clearance is to much you will loose a lot of oil pressure and it might be a good idea to rebuild it or replace it


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[RiverandSand]

It doesn’t look like it has spun, its old and worn but not worn out.....


Go to the parts store and get some plastigage and take a reading of the bearing clearance, if the clearance is to much you will loose a lot of oil pressure and it might be a good idea to rebuild it or replace it


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WOW
What he said!
I can't imagine the oil pressure was to good either.
On the back of the bearing it should have the size listed, that will tell if the crank was turned or not.

 

[inthegarage]

I thought the oil pressure gauge was broken when it did run because it always read zero. Now you've got me worried it was running with no oil pressure.

Thanks for the help guys!

 

[gert]

I thought the oil pressure gauge was broken when it did run because it always read zero. Now you've got me worried it was running with no oil pressure.



Thanks for the help guys!

Check your clearances that where you need to start, if the clearances check out good I would run it


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[inthegarage]

Check your clearances that where you need to start, if the clearances check out good I would run it


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Thanks for the hint on plastigage. I dove into the FSM and it describes how to use the plastigage to determine the bearing clearance. But I'm not sure what spec I should compare it to? The FSM has "Crankshaft Clearance Limit New" value of 0.0005" - 0.0026". Is that the value I should be looking for, does that sound right?

If that reading doesn't match up, then I assume I have to buy undersized bearings? Is that a common thing? Will the guy at the parts store look at me like I'm crazy?

Sorry for the dumb questions. I feel like I know just enough to be really dangerous and want to take the proper precautions.

 

[gert]

Yes .0026 sounds right, if it’s to much more than that like .0045 or something you will need to look into how good the crank looks what the other bearings look like what their clearances are


You might be able to get away with replacing the bearings with the same size you have now which will be stamped on the back of the bearings

If your crank feels scored up it will eat new bearings up same as the ones that are on it now at which point you have to machine the crank......

If your pulling the crank to machine it you might as well think about rebuilding or replaceing the motor

From what I saw in your pic the crank looks good


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[Lumpy Grits]

Never trust the OEM, OP gauge.
Crankshaft looks good.
Pull a couple more 'caps and have a looky-see.
Make sure you mark the caps so they go back on in the exact placement they came from.
LG

 

[coldair]

Never trust the OEM, OP gauge.
Crankshaft looks good.
Pull a couple more 'caps and have a looky-see.
Make sure you mark the caps so they go back on in the exact placement they came from.
LG

Just what Lumpy said and make sure you mark them so they are also facing the right way they have to go on the same way they come off. cap has to face the same way as you take it off.

 

[cglax6]

Just what Lumpy said and make sure you mark them so they are also facing the right way they have to go on the same way they come off. cap has to face the same way as you take it off.

Yes to all of this and what LG said...

Bearing is shot...the other half will look chewed up like that one. From what I can tell on the crank, it still looks good.

If it were me, and I still wanted to use the engine, I'd rebuild it. If you dropped the oil pan and a bolt was just hanging out in there, that would scare the bajeebus out of me.

I'd pull the engine, take the crank out, have the crank inspected and worked by a machine shop, if needed. You can have them order new bearings based on if they need to work the journals or not. I'd also take a good look at the cylinder walls as well. If you're pulling the crank to replace bearings, you may as well pull the pistons too.

Has the engine been rebuilt before? If not, it might need an overhaul anyway. Dead giveaway is the bolt in the oil pan!

Let us know what the rest of the bearings look like...the one you showed is pretty chewed up.

 

[cglax6]

I thought the oil pressure gauge was broken when it did run because it always read zero. Now you've got me worried it was running with no oil pressure.

Thanks for the help guys!

You'd have catastrophic failure if you had zero oil pressure. You most likely have a bad sensor, gauge, or wiring.

And if you end up rebuilding the engine, or any part of it, look up Pete's Garage on youtube. He has some excellent videos of engine rebuilds, and a set in particular of him rebuilding a SBF and explains every step in detail that can be applied to your motor.

It'll make you that much more dangerous...

 

[inthegarage]

Well, I'll be honest.

The broken bolt in the oil pan spooked me quite a bit. It must have been broken for a little while as the broken end worked itself free from the block, so I have both parts of the bolt, weird.

My original plan was to clean this thing up, slap some new gaskets on and get through another year or so.

But given the multiple recommendations for a complete rebuild, I'm crating it and saving it for another day/year/decade. It just really didn't make sense to me to pour so much work and money into an Iron Duke just to get 84 hp back (if I'm lucky). One day, I might use it as my first rebuild, because I won't cry if I screw it up, but for now, it's going to live in the corner of my garage.

So, the SM465 I've rebuilt will now go behind an LS.

If anyone is in the market for a well worn GM 151 Iron Duke, you know who to contact

As a side note, I always read that the Iron Duke was a Pontiac small block cut in half. It made sense, but I had rotated the engine to get the bearing out the other day and this angle caught my eye. It really does look like half a small block!

 

[cglax6]

But given the multiple recommendations for a complete rebuild, I'm crating it and saving it for another day/year/decade. It just really didn't make sense to me to pour so much work and money into an Iron Duke just to get 84 hp back (if I'm lucky). One day, I might use it as my first rebuild, because I won't cry if I screw it up, but for now, it's going to live in the corner of my garage.

Bummer!

Best case scenario: The bearings are shot, and the crank is fine. When you pull the pistons, and inspect the cylinder walls, they look good. No weird scratches or dents in the valves or top of the pistons. If all is well, you're paying for new bearings, an oil pan gasket, a machine shop to measure and verify what bearing size you need, and maybe new piston/oil rings. Max $400...and that's a high estimate. If you're real nervous about the crank, pull one and have it inspected or honed by a reputable shop. I know it may be hard to find one, but there are a lot of good Jeep yards around the country that should have some laying around.

You may have just got lucky that the bolt just sheared and caused no other damage higher than the bottom of the oil pan.

The noise you were hearing before was probably due to that cap not being secured all the way down.

I think it's worth a try...especially if you have to source a whole new engine. If it's cheap to fix what you have, and you still want a new motor in it, you can take your time with the new one. It doesn't take too long to tear apart for a look-see.

Just my opinion though...