Jerry From LA
Jerry From LA UltraDork
1/10/24 10:37 p.m.

Hey Everbody,

A co-worker pulled the 5.3 liter LM7 out of his truck to tear it down due to "terminal valvetrain noises."  Sure enough, a cam bearing came out with the cam showing evidence of having spun. There were also issues with adjacent roller lifters and some cam damage.

The question:  Is there any way back with this block or is it scrap?  I don't have pics but the back of the bearing has score marks on it.  How can he assure a tight enough bearing fit if the block is saveable? Is this a known issue with this engine?

I've built 17 motors but only one had pushrods and it was a B20 Volvo. Total caveman stuff, comparitavely speaking.  That one didn't have bearing seating issues.


Ranger50 MegaDork
1/11/24 6:52 a.m.

Given they are plentiful still, I'd call it scrap and find another.

Edit: I mean you can fix it but then you are going to need a bearing set that fits after finding out what the spun bearing diameter is. You can go with a 55mm roller bearing possibly and eliminate most of the issue. But then you have to line hone the cam tunnel at probably $200, bearings at $100, new compatible camshaft at $500..... 

Streetwiseguy MegaDork
1/11/24 8:21 a.m.

Not worth fixing.  The junkyards ate full of rebuildable engines that don't need specialized machining and custom bearing parts.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) GRM+ Memberand MegaDork
1/11/24 1:02 p.m.

It can be fixed, but likely not for the $250 cost of just getting another block.

The way it's fixed is to overbore the cam journal and use oversized bearings.  Pretty common back in the day.

First gen Vipers didn't have cam bearings.  The cam rode directly on aluminum in the block.  As you can imagine, billet steel spinning in aluminum didn't last long.  The fix was to overbore it and install AMC cam bearings since they were the right size.

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
1/11/24 8:12 p.m.

I had this happen with a 3800 Series II.  Just lost all oil pressure one morning.


Pulled the engine, installed new cam bearings, engine is still good ten years later.  No oversize.

newrider3 HalfDork
1/11/24 8:49 p.m.

Peen the cam journal in the block with a punch for a tighter bearing fit; or use sleeve retaining compound?

GaryC83 Reader
1/11/24 9:32 p.m.

In reply to newrider3 :

That's the fix for early L92's. They like to push the cam bearings out as well. My Escalade did it at about 125k. 

RacetruckRon GRM+ Memberand SuperDork
1/12/24 12:59 p.m.
Curtis73 (Forum Supporter) said:

First gen Vipers didn't have cam bearings.  The cam rode directly on aluminum in the block.  As you can imagine, billet steel spinning in aluminum didn't last long.  

Except this is exactly how nearly every single OHC engine operates without issue.  There was probably some less than ideal engineering decision made on Gen1 Vipers and the problems weren't completely flushed out given the developmental resources. But let's not go and make bold, generalized claims like that when that is clearly the exception not the rule like it was stated.

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
1/12/24 9:46 p.m.

In reply to RacetruckRon :

OHC engines have much different loadings on the lifters than OHV.  Some OHV camshafts actually have flexing issues from all of the loads (looking at you small block Chevy)

RacetruckRon GRM+ Memberand SuperDork
1/12/24 11:37 p.m.

In reply to Pete. (l33t FS) :

They absolutely do have different loading, journal sizes, cam lengths, etc. but my problem is with Curtis' generalization of aluminum soft, steel hard = no work.

Jerry From LA
Jerry From LA UltraDork
1/13/24 10:32 a.m.

I think Curtis was referring specifically to Chrysler's inappropriate use of the technology in that particular application rather than a condemnation of steel cams riding in aluminum generally.  His knowledge runs deep on many automotive fronts.  An OHC head can be corrected or replaced rather easily if it wears badly compared to a block.

My co-worker said he "felt grooves" in the bearing land. I don't know if this engine has a passage behind the bearing or just an oil feed hole. That is what prompted this thread.

Run_Away GRM+ Memberand Dork
1/14/24 3:54 p.m.

I've head this seems to be a more common issue on 6.0L iron blocks. I'd toss in a new bearing with some green loctite (sleeve retaining compound) and run it.

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