Web Cracks

[450]

Longtime Lurker.....first time poster....anyway...how many of those that have broken crankshafts also ripped the center mains out of the block?...happened to me at freeway speed, in overdrive, good oil pressure not overheating...harmonic balancer looks ok...All of sudden, a little hammering, loss of power, hammering gets louder, motor locks up. Yep..it sounded as ugly as the pieces in my oil pan looked. Is it possible that the dreaded cracks in these motors let loose causing the broken crank...or is mine the exception?...to be fair the motor had at least 184,000 on it...Now I have a good running/sounding spare motor with 375lbs compression in all cylinders, but it has the cracks too....is it just a time bomb if I use it?....

[odee]

my 87 sub had around 325-425 on the engine when the crank let go a few years ago. I bought it used and rode it about two years before this happened. Since then I have bought just about every 6.2 piece in my neck of the wood that I had ran across. I have about 6 block here now with the same cracks and or broken cranks with the cracks. I hope someone with more time with these engines will put some more info out about this problem.

[britannic]

One alternative is to hunt for an early "red" (painted) engine or a genuine CUCV military block, these had a higher nickel content and were very resistant to cracking. My military block is still crack free after 170K plus miles. The more expensive route is to find a 6.5L 599 block or buy one of the new Hummer 6.5L replacement engines.

[odee]

I have one of the early red engines in my sub right now, bought it from a guy who was swapping to a gas engine for 200 dollars put a different pump on it been riding it for about 6 or 7 months now. Has anyone had one of the red blocks checked to see how thick the cylinder walls are in them? Just wondering I have run across two more red engines that I can pick up cheep or next to nothing for them. If they checked out to be plenty thick I was thinking of boring one to take my 6.5 parts.

[450]

Thanks for the replies....was able to come up with a "red" block....its been sitting 8 or 9 years...pulled it apart....small cracks in one web, but no where as bad as the 84 I had...gonna run with it and see what happens. Tempted to convert to a gasser as I have a complete Sub with rusted body and a fresh 350...but I do like the diesel, plus I had already invested the new injection pump, injectors, headers and 3 1/2" dual exhaust into the blown motor. Still wondering if the cracks caused the crank to snap though......

[odee]

I to have pondered the thought of rebuilding one of the cracked blocks that I have. Who knows how long I drove or the p/o drove my sub with the main webs cracked. The last time I was at my father in laws in Almont-Mi. I ran across two 6.2 diesels at the salvage yard there in town. He was wanting about 275 apiece for the ones that were out of the trucks. I don't know the name or number for the place thou.

[Diesel Dan]

I pull a '599 block out of a '93 I had. The motor was froze up, #3&4 rods siezed up. Block had the small cracks about 1/4-1/2" long on the #3 main web outter bolt hole. Motor had 227K miles on it.

From what I could see part of the crack problem is the holes weren't chamfered. This leaves a sharp edge and stress risers which leads to cracks. Also witness marks looked like the caps were walking around at the mating surface of block/cap.

[Dezman125]

Hi
If anyone decides to use a block with cracked webs,their is a stud and girdle setup for the main bearings,it ties all the main bearings together with some high strength steel plates.I'm not sure where you would find them in the states,the machine shop i deal with has them advertised on thier wall.
I will bw installing them with my turbo,if i everfind all the pieses i need.Seems like cheep insurance to strengtheen the bottom end

[450]

I do not like the idea of useing a block with the cracks, but out of the three I have all have them...seems way too common and I wonder if it has more to do with the bottom end problem on these motors then there given credit for...I.m sure a bad harmonic balancer does'nt help things, but mine looked pretty good and still grenaded the bottom end...kinda scary to know they are there and still use it, but there are no turbo plans in my future and the cracks are minor..I remember Dr. Lee talking about running his with cracks prior to his new motor...but he didn't say for how long....anybody else run with cracks and if so, how long did it last?

[NH2112]

The block I took out of my K10 had 290K miles on it and all the main webs had BIG cracks. It never gave me a bit of trouble, though, and if I'd needed to I would have put it back together and run it without any worries.

[odee]

I've got about 4 0r 5 6.2 and 6.5 block with the mains cracked in them. Two had broken cranks the others just block damage on the mains. Could it be from the lack of the bolt hole not being chafered as said above or just not enough material in the block casting? Will the studs and girdle help out a lot or is it just a added insurnace item?

[cubby]

I have a 85' 4x4 with about 250,000 miles. This truck has plowed snow every year of its life. I just bought a CUCV engine with 70,000 miles, I,m planning to do the swap in about 2 months. I can't wait to tear down the old motor and see how bad it is! (or isn't)

I have been running my other plow truck with the 6.5 with 6.2 bolt on stuff, and it has been running real good. 700-800 miles so far :D