Main Bearing failure help :(

[Mikeandwendy74]

Ok, oil cooler line went bye bye, now motor runs pretty good but not really good, pulled motor, off with oil pan, found only 1 crank bearing that suffered damage. it is not totally demoished but it is grooved now, and metal has been shaved. The crank journal is just barely scored, if feeling with finger, you can barely feel grooves. Does this mean the crank is shot? can I just slap in new bearings? Will the crank chew the new bearings up? Should I have the crank polished...will that even help? By the way the block is perfect as far as cracks around the main webs go, I cleaned real good and tried the torch trick. Any help and advice is GREATLY appreciated. Thanks for looking.

[AKMark]

I've had two 6.2's spin bearings. I would have it polished, you never know how long it's gonna be before it gets looked at again, and a little insurance never hurt.

My two were weird. First one happened on a motor with over 300K on it. It ran fine, but two days before the oil pressure gauge had stopped working. I verified it had pressure with a manual gauge in the shop, but had removed it to drive. Then it just died twenty miles from home on a -40 night. Not good, had all three kids and the wife with me as well. Luckily a buddy got up there within thirty minutes and we always keep blankets in our vehicles. The second one was on the rebuilt motor. I was moving from Alaska to California, and had approximately 5000 miles on it. I was pulling a really heavy trailer that had no aerodynamics whatsoever. Top speed was 50 mph, and frequently it would shift into second at that speed attempting to keep speed up on the hills, normally it would drop to almost 15 mph up the steep inclines. It was doing a good job, good oil pressure, no overheating, EGT less than 800, and the built 700R4 was doing it's job well. I had to stop at a rest stop at the top of a large hill to allow a passenger to utilize the facilities, and decided to let it idle and cool off after the hard pull. The stop ended up taking close to 15 minutes, and the oil pressure had dropped to almost 10 psi. When I pulled away, the #1 rod bearing spun. 300 miles from where I was moving to. Not good, a real PITA.

I had used a resurfaced crank during the rebuild and had built it to the proper tolerances. I can only imagine that the oil had overheated during the hill climb and caused bubbles that smoked my bearing.

Moral, don't mess around, do it right.:o

[Robyn]

As long as no bearings spun in the block or any rods you should be fine to pollish the crank and replace the shells.

If you dont need to remove the heads and such you can stuff the pistons up into the block and yank out the shaft and then do your work and then replace it.

Might be a great time to clean it up and check the heads and do gaskets and such as well as a timing chain, rocker buttons and a few other goodies while its out. Maybe new soft plugs as these are usually toast after 100K.

Best of luck

Robyn

[Mikeandwendy74]

thanks for the advice, one question for ya, when they"polish a crank, are they removing some of the journal? will the bearings need to be oversized? the bearings that are in the block right now are stamped with the following
FM letters are in a circle
3861-AP-L

.25 US

9 99

Any clue what these numbers mean?

[Robyn]

The bearing you mentioned is a .25mm undersize.
These engines use select fit bearings on both the rods and the mains.
The mains can be standard or U S and the rods can be standard or U S
there is no rhime or reason. They just used this to make up for sloppy machine work.

The factory undersize bearings are .0005" and .001" US

.25mm is actually a .010" UNDERSIZE (Cranks been ground)

A millimeter is .03925" so divide by 4 and its about .0098" US or in SAE it would be rated as a .010" US

The clearance can be as much as .004" on these so unless you are really taking a buttload off the crank you should be fine.

I would Mic the crank and see whats what and then with things dry do a plastigauge and see what you have

These engines are better off a little loose as opposed to being tight.


Best

Robyn

[ronniejoe]

I know on small blocks, you can get .001 under bearings for just such a situation. Don't know for sure on 6.5's though.

[Mikeandwendy74]

Thanks for the info. I pulled both heads off going to go with a full rebuild I think we'll see :)

[Robyn]

GM offers a select fit bearing for mains and rods is .0005" and .001" U S but they are spendy as compared to aftermarket stuff like Cleavite, ect.

The size you gave .025mm indicates that you have a ground crank and a .010 Approx undersize already.


Best

Robyn

[Mikeandwendy74]

so if the crank was ground thats not a good thing i take it.... hmmm I guess my main question is if I polish it can I get the same size bearings and simply replace them? or should I look for a replacement crank...whats your opinion?

[ronniejoe]

We grind 6.5 cranks 0.010 under all the time.

[Mikeandwendy74]

We grind 6.5 cranks 0.010 under all the time.

I think i'm finally getting the concept of the needed size bearings....i think, so if the crank is ground .010, then the .25 bearings that I have right now in the block are actually OVERSIZED bearings for an UNDERSIZED crankshaft...yes?

[Robyn]

a .25mm undergrind on a 6.2/6.5 is just fine. The issue is that the radius in the fillet has to be maintained.

Many folks talk about losing the tufdriding on the surface.
These are Nodular iron shafts not steel and the Tufdriding is a chemical hardening process done on steel shafts.

If your crank is not scored and will pollish up good just be sure the bearing clearance is within specs and your set.
As I mentioned before, a little bit loose wont hurt these engines at all.
Better to be on the top side of the spec than the bottom.

Tight bearings just make me nervous.

I set my Burb at about .003 across the board and it is sweet.

best

Robyn

[Mikeandwendy74]

Well after 3 laborous hours of complete dissasembly, heres what I found out about running out of oil ughh:

2 spun connecting rod bearings
1 chewed up main bearing which suprisingly enough to the naked eye did not do much damage to journal(didn't spin just got burnt)

no damage to camshaft lobes

1 broken top ring(compression ring?)

piston bores look smooth as glass and need to be rehoned no more crosshatch pattern

3 pushrods that need to be replaced(not bent) just worn at the top a little bit.

lifters look good but still need to pressure test em'.

pistons are a little carboned up but look good.

connecting rods look ok will have them checked out.

I might be able to get away with a few parts and a new crank.

heres the question, with a bore guage how can I tell if the rings are standard or oversized? anyone know the standard bore diameter for a 6.2?
and will a 6.5 crank fit in a 6.2?just curious
any help is appreciated thanks

[Robyn]

Running out of oil always comes at a price, no matter what.

A couple rods and a crank, some bearings, a set of rings and gaskets.
New head bolts, push rods. Hmmm
Major overhaul.
Now make sure you install the pushrods with the copper colored ends to the top

Robyn

[john8662]

I think the best answer for the questions about the engine should be acquired at your favorite local machine shop.

I'd have them look at your crankshaft for the difinitive answer of whether it'll polish, or have to be ground, again. If so, I'd suggest finding another crank, for a 6.2L. If you have a 2-piece rear main seal, you have to use a 6.2L crank for a 2-piece block, a 6.5 crank will not work. All 6.5 cranks are single piece rear main seal units.

Get the block torn down completly, remove the camshaft, etc. You'll likely need new cam bearings too considering your oil loss, so this needs to be done too.

Take the block to the machine shop, have them mic the bores with their cylinder bore gauge, this will give you the correct answer on what's oversized and what isn't. They'll need at least one of your pistons. The shop should have access to the AERA specifications on the 6.2L Diesel. This will grant them STD size and enable them to do the math from there.

The block needs to be hot tanked and cleaned out, this will clean out metal debris from bearings gone south (or further south in the pan).

Two of your rods need to be resized due to the spin, but I think the best solution would be to find suitable replacements. Ask if they can match the length of the rods when they refurbish and resize the large and small ends.

The should can also likely assist in getting parts too.

J

[Mikeandwendy74]

Thank you sir for the information I appreciate it.