6.2 Rebuild Advice

[welpro222]

I'm in the process of rebuilding my 6.2 Diesel and want to know whats the best Main and Rod Bearing and Piston Ring Manufacture?

 

[91W350]

Before you get too far, have the block checked for cracking. Why does it need rebuilt? If it lost main bearings, you may be out of business. Glen

 

[welpro222]

Yes of course, block will be inspected first. The motor came out of a 1985 Suburban parts truck. The guy said he ran it out of diesel and could not get it started again. then he used Starting Fluid and said it ran for a bit that died. Anyways regarless i'm rebuilding motor so I have something fresh. So far I have broke down the engine to the bare block and its nice looking. Its a 1991 year 660 Block. The heads were in good shape and are at the machine shop at the moment for bath, inspection, and new valve seals.

 

[welpro222]

Also what do you guys think of the Main Stud Girdle? Worth it or a scam? I'm going to buy the ARP Studs for the heads.

 

[airmech]

For bearings my preference is clevite, rings - perfect circle, pistons - maule (armoured top groove, fully machined and anodize hardened). The stud girdle is definately worth it if you can still get it. I've heard DSG no longer sells the 6.2 girdle and timing gear kit. As stated, check everything out first. The crank can not be machined, so make sure it is within tolerance before spending any money on parts.

 

[ODdave]

Why can you not machine the crank?

 

[papercu]

Why can you not machine the crank?

This is from google
How many miles out of your 6.2? [Archive] - Diesel Place : Chevrolet and GMC Diesel Truck Forums Wayne

 

[67_C-30]

The crank is nitride coated, and cannot be turned, per orignal GM literature.

 

[ODdave]

odd........the military turned them....

 

[760gamemaster]

you can turn a nitrided crank it just wont be nitrided anymore.

 

[welpro222]

Well found out what happen to my other engine. Pulled the passenger side valve cover and found a bent pushrod on the #4 piston, and the rocker shaft broke off (weird). So tonight I pulled the head and saw a huge hole in the cylinder wall and the piston was mangled to pieces. Not only that the connecting rod manage to bend in half and jam itself between the block and crank. I'll have to post pics soon. That explains why I couldn't turn the motor over. I'll pulled the oil pan and see if I can remove the connecting rod, and i'm sure i'm going to see a cracked outer web.

 

[ODdave]

if there is a hole in the cyl wall i probly wouldnt worry to much about the cracked web.......

 

[welpro222]

I know that, I just want to know the cause of failure.

 

[DXTAC]

If it's down that far I'd go with a Scat crank, ARP cylinder head studs, Mahle pistons and either Phazer or Pete Jackson gear drive. My

 

[67_C-30]

odd........the military turned them....

you can turn a nitrided crank it just wont be nitrided anymore.

Sure, you can turn them, but it significantly decreases durability on an already weak crank. It also partly contributed the high amount of failures in the earlier HMMWV's. The 6.2/6.5 cranks are made of nodular iron, and they are heat treated and annealed to have ductility. The journals are then nitrided for wear properties. This combination allows the crank to be hard enough surface to resist wear, but remain ductile enough to resist the shock loads of the high CR of these engines. This was the "next best thing" used in place of the forged steel crank that Detroit originally designed for this engine. (Detroit also desgned it to have a high nickel block like they used in 1982, and the main cranking is almost non-existant in those blocks). GM bean counters had way more to do with poor reputation than the actual design did.

I personally would not turn one of these cranks with that in mind. I always look for a decent crank that maybe needs polishing (which is OK) but I wouldn't turn one without having it re-nitrided which would not be cost efficient. There are too many good cranks out there for reasonable prices.