Would you use this cam bearing?

[JHZR2]

This is an offshoot of my diesel misfire thread found here:

https://bobistheoilguy.com/forums/threads/mercedes-diesel-misfire-after-hg-replacement.384310/

However it is more general interest, so I figure a separate thread may be useful to others.

I had a broken camshaft, as can be seen in the linked thread. I think it was tightened down wrong.

Here’s the bearing that was over the break (some call it the cam tower):

There is a little line that can be seen, in the middle, in the direction of rotation. But there’s also a perpendicular scratch, seen in the bottom most photo, and some “speckles” from foreign debris, probably there when the crack first happened (and subsequently flowed out, no debris present.

I can’t seem to feel any of it with a fingernail.

Is this bearing useable?

Is it useable with a new cam?

Is it useable with a good used cam?

Will a good used cam wear in its surfaces and asperities with the surfaces and asperities of this bearing?

There is plenty of thickness left on the bearing from what I can see.

Thanks!

 

[zzyzzx]

How much is a new one?
How many miles are on the vehicle?

 

[emmett442]

Looks like there is no bearing shell: the machined cam cap itself is the bearing. In that case, you have no choice but to run it or replace the entire head. The cam tunnel is align bored with the caps in place. They are mated to that head, in that position for life. You cannot mix-match, or replace them unless you have the machine work done.

That said, I don't see much of concern. I'd roll with it.

 

[demarpaint]

If going through all that work to install a new cam, I'd be replacing that bearing with a new one. Used cam?: If it was the bearing mated to it, maybe. Odds are my OCD would have me replacing the cam and all related parts with new.

 

[Highlander 1459]

is the bearing cap the bearing? or is that a bearing shell in a bearing cap?.
if I had it apart that far I'd replace it, even if it is the top bearing and doesn't carry much load..

 

[JHZR2]

How much is a new one?
How many miles are on the vehicle?

Unknown availability, >30yo engine, 116k.

Looks like there is no bearing shell: the machined cam cap itself is the bearing. In that case, you have no choice but to run it or replace the entire head. The cam tunnel is align bored with the caps in place. They are mated to that head, in that position for life. You cannot mix-match, or replace them unless you have the machine work done.

That said, I don't see much of concern. I'd roll with it.

That’s super important insight.

I wasn’t sure if the machined cap still has some sort of babbitt coating on there. But the proper alignment which I assume affects oil flow, does seem super important!

If going through all that work to install a new cam, I'd be replacing that bearing with a new one. Used cam?: If it was the bearing mated to it, maybe. Odds are my OCD would have me replacing the cam and all related parts with new.

Tend to agree. But cams on these engines aren’t a known weather point. In fact, they look like new with 300-400k on them. I’ve seen a number of them in person. I have all variants of this engine (4/5/6 cyl) and the cams all look perfect.

So my thought is this - since I don’t 100% trust the workmanship situation right now, change the cam (30 min job working slow) with a junkyard/free cam
That has higher mileage, turn the engine by hand, run the engine some, then once all is certified ok, then change to a better new/low mileage used cam and new lifters.

Because cam swap is so easy, and a new one cam is $600, I’d prefer to manage my risk in getting the engine up and running.

 

[JHZR2]

is the bearing cap the bearing? or is that a bearing shell in a bearing cap?.
if I had it apart that far I'd replace it, even if it is the top bearing and doesn't carry much load..

It’s the bearing itself. I didn’t think about loading. Wouldn’t the loading actually be upwards, since the cam is acting down on the lifters?

 

[RedSpider]

Looks like there is no bearing shell: the machined cam cap itself is the bearing. In that case, you have no choice but to run it or replace the entire head. The cam tunnel is align bored with the caps in place. They are mated to that head, in that position for life. You cannot mix-match, or replace them unless you have the machine work done.

That said, I don't see much of concern. I'd roll with it.

I agree with this 100%.

If you cant catch the scratches with a nail, run with them. Like he said, you cant just replace these with another, they are line bored to that head. A machine shop could probably make a replacement work, with a lot of custom work on their end, but you're pulling the head in that scenario.

Replace the cam, use the existing bearing caps, and if the oil pressure is ok, I wouldnt be too concerned. Just my $0.02.

 

[demarpaint]

So my thought is this - since I don’t 100% trust the workmanship situation right now, change the cam (30 min job working slow) with a junkyard/free cam
That has higher mileage, turn the engine by hand, run the engine some, then once all is certified ok, then change to a better new/low mileage used cam and new lifters.

Because cam swap is so easy, and a new one cam is $600, I’d prefer to manage my risk in getting the engine up and running.

OK, put that way changes things a bit. It makes more sense to me now. Interesting project!!

 

[Highlander 1459]

It’s the bearing itself. I didn’t think about loading. Wouldn’t the loading actually be upwards, since the cam is acting down on the lifters?

yeah, you are correct. I'm thinking of a crankshaft, where the load is mostly opposite..
it almost looks like it has a place for thrust bearings.

 

[ARCOgraphite]

Knock down any high points, don't be too aggressive.
Striations etc, hold oil = good.

Insure assembled shell diameter provides for correct bearing clearance.

You will be limited to certain machinists/shoppes if they require resizing

 

[ripcord]

I think I would at least torque that cap into it's spot and mic the inside diameters at several different locations just to make sure it hasn't been distorted and is nominally in spec. It seems to me like that journal may have been subject to lots of stress if the camshaft was broken there.

 

[SC Maintenance]

Plastigauge. They still sell it. There will be a clearance spec in the manual.

Or is that a lost art now?

 

[Malo83]

No !

 

[cptbarkey]

how does it compare with the others?

 

[JHZR2]

I think I would at least torque that cap into it's spot and mic the inside diameters at several different locations just to make sure it hasn't been distorted and is nominally in spec. It seems to me like that journal may have been subject to lots of stress if the camshaft was broken there.

Good point. I can do that easily with the cam out.

I think it snapped on tightening the cam towers, the cam snapped, and the one side spun while the other side didn’t.

I’ll put a micrometer on it as well. Thanks!

No !

Why?

how does it compare with the others?

good question. I’ll look for specs and do some measurements.