6.2L ran out of oil... what can I expect?

[Quack_Addict]

I have a 6.2L J-code from a 1987 3/4 ton Suburban. The engine was spent when I got the truck - previous owner's kid ran it out of oil (maybe 2 qts oil in the pan). I replaced the engine some time ago with a 6.5L.

Anyhow, the 6.2 has been sitting on an engine stand untouched since pulled. I had to drop the oil pan and loosen the rod/main caps to turn the engine over enough to get the torque converter bolts out during removal from the vehicle. There were several chunks of shrapnel (thin pieces of bearings about like aluminum foil) in the bottom of the pan.

Is it possible that this is a rebuildable engine? I realize the crank would need some amount of machining, if it's any good at all. What about the block, heads, etc?

[britannic]

FYI: the crankshaft is nitrided and cannot be machined, only polished.

[NH2112]

I'd go ahead, pull it apart, and start measuring. Cranks go pretty cheap on eBay so if everything else is OK (and the idiot bidders don't come out in force) you could have yourself a spare engine, or one for a project.

[CleviteKid]

The Brit is correct, the crank cannot be MACHINED in the lathe sense of the word, but it can be GROUND undersize, but then it is worthless, except as a doorstop.

If the bearings have been extruded out, then the rods are also shot, and maybe the main saddles also.

Without lube long enuf to extrude bearings, the rings have probably gouged grooves in the cylinders, and the valve stems may have taken out the valve guides in the head. The intake manifold is probably still OK . . . :rolleyes:

Dr. Lee :cool:

[Dieselboy]

There's a guy in my local off-road club that bragged to me about how well he built his 6.2L. Everything sounded good until he mentioned that the crank was turned .010/.010. :eek: Depending on the steel, case depths range from .005 to .020, and since the material under the hard nitride surface is soft and ductile (impact resistant), the overall strength of a machined crankshaft is drastically lower.

The process of nitriding is darned neat. It's one of the lowest temperature treatments (~950-1000*F), the part is allowed to cool slowly without a quench, and yet it produces the highest wear resistance of all the diffusion methods (70 HRC is easy with Nitralloy 135).

Dr. Lee:
I am curious what our cranks are made of - 41XX, 43XX, a Nitralloy, or something else?

PS: I am studying for a test tomorrow in a materials science class, and part of it covers diffusion treatments. When the professor said that we were going to be talking about nitriding, I stopped doodling in the margins and paid attention. ;)

[CleviteKid]

Calm down Dieselboy, and stop day-dreaming about chrome-nickel-molybdenum alloy steel forgings. Our cranks are high-quality nodular cast iron with a fine pearlitic matrix.

I am teaching Materials Science this semester at U of Miami, and always look for a few gearheads in the class to keep it interesting. Wish you were one of them; we would have a blast at the expense of the other students.

Dr. Lee :cool:

[Stage1]

Hi Doc,

Agree this type of crankshaft material can perform very well. I believe my 70' Buick 455 crank is made of similar material. It is a "D" S/A stocker that turns 6500 RPM w/ about 14 to 1 compression. Stall speed is about 5500 RPMs, car weights about 3950 lbs., so it takes a little shock when the light turns green :eek: No problem w/crank, with proper oiling modifications.

Les

[Quack_Addict]

I am going to start the disassembly sometime soon to free up the engine stand for another SBC build; possibly start on it tonight. At least I can look forward to the intake and coolant crossover still being good. :rolleyes:

I didn't notice complete bearings extruded out, just foil thin pieces of them munched up like scrap paper. Hopefully this wasn't enough to friction machine the sides of the rods near the crank journals.

Are the 6.2L head bolts TTY (torque to yield) and/or worth saving? Is it likely the fuel system (injectors) may have been damaged?

[Quack_Addict]

Never mind on the TTY bolt question... I just read Brandon's post.

[bio-diesel]

I don

[CleviteKid]

Remember all the information about bad torsional dampers leading to broken crankshafts? That is because torsional (twisting due to torque) stresses are what can break cranks, and the damper is like putting a rubber coating on a bell - it cuts down on harmful resonance that can amplify stresses.

The hard layer on the outside of the crank is also very strong and fatigue-resistant. This is MORE important that the wear resistance - since the bearings with a soft babbitt coating are designed to wear to protect the crank. For occasional racing (strip, street, doesn't matter) the number of stress cycles accumulated is not that great. But try towing a large camper back and forth across the Rocky Mountains and you will be subjecting the crank to LOTS of high stress cycles, and fatigue resistance becomes very important. For any diesel engines that the members of this club are rebuilding, we recommend that you INSIST on polishing ONLY of the crankshaft - no turning or grinding allowed. Let some non-member buy those cranks.

Dr. Lee :cool: a.k.a. The Clevite Kid, for good reason ;)

[JeepSJ]

Be careful with cranks on e-Bay. When I was trying to decide between buying and building, I contacted more than a few people who were selling cranks. They typical response was "it is a little rough, but it will clean at 10/10". I also talked to many rebuilders, and nearly all admitted to turning the crank 10/10. I think Avant was the only shop I found that didn't grind their cranks.

[bio-diesel]

Sure resonance/vibration will kill an engine or for that matter any machine running at high speed, the harmonic vibrations magnify the affects of stress. Back the question of grinding the hardened layer, nitriding is a bearing surface treatment it doesn

[CleviteKid]

Nitriding, carburizing (a.k.a. case-hardening), carbo-nitriding, burnishing, shot peening, flame hardening and induction hardening are all surface treatments, in that their effect is limited to a zone near the surface of the metal component being treated.

Why use these surface treatments on things like axles, Colt revolver frames, leaf and coil springs, typewriter (remember them?) keys - the ones that push the ribbon against the paper, not the ones your fingers push, crankshafts, u-joints, gear teeth, roller bearing races, etc. etc. ? One reason is for added wear resistance from other components rubbing against them. But do you think Col. Colt really was worried that drawing and reholstering your revolver was going to wear it out? If so, why not case-harden the barrel too?

The main reason is for added strength at the surface. In either bending or torsion, the major loading modes for most real structures (crankshafts are loaded in BOTH bending and torsion) the highest stresses are at the surface. It is well-known that fatigue resistance is proportional to ultimate tensile strength and hardness, for any given surface roughness. Ductility is not a concern for fatigue, where no macroscopic deformation is involved anyway. All these treatments listed above make the surface layer of a metal harder and stronger, and many of them also create favorable compressive residual stresses to better resist the initiation and propagation of fatigue cracks.

In particular for crankshafts, the fillets adjacent to the cylindrical journals are nitrided, shot peened, roller burnished, etc. for added fatique resistance. The bearings never touch the fillets (except during bearing failures !) so wear resistance of the fillets is not an issue.

Dr. Lee :cool:

[CleviteKid]

Attention Bio-Diesel:

If you want to continue this discussion, please start a new thread in The Members Forum.

Thanx, Dr. Lee :cool: