Broken Crankshaft

[Beedee]

Friend of mine just broke the crank in his 92 1 ton :eek:
I've seen a few posts about this.
How wide spead of a problem is it.
It has a 5 speed manual tranny
His wife uses it to pull a horse trailer, and the Mech working on it thinks that it has something to do with pulling the trailer with a gearjammer, nothing in the way to absorb the shockload from accelerating and decelerating.
I know that in the large off highway trucks I work on, when we went from the 2 cycle engines to the 4 cycle, we had to put a rubberized coupler between the engine and the torque to absorbe the shock, but that was to protect the tranny.
Any thoughts?

[Jim P]

My 95 had a broken crank when I bought it. It also has a 5 speed trans. but I don't think that is the reason that it broke because the break was up towards the front of the engine. I would think that if torque is breaking them, it would be in the back, close to the flywheel.

I think the reason they break is just because the crank is not strong enough to handle the high compression that these engines have from the factory. The 6.2 engines broke cranks even without the added stress of the turbo and a 6.2 and a 6.5 crank are the same.

The front balancer and crank pulley are known to fail and ad to crank failure but both were good on my truck when the crank broke.

[C.K. Piquup]

I`ve owned 3 6.2 and 2 6.5TD GMs over the last 16 years without a broken crank.I hope my luck holds out.It has happened to more than a few,both auto and manual.There`s alot of speculation,but no definative explanation.These cranks are nodular which is a very tough material.They are not to be machined.Most feel the cause is in a deteriorated harmonic balancer.The manual trans theory is bunk.A manual trans is a great way to go for towing.

[Kennedy]

Typically we see cracked blocks prior to broken cranks. Mine tore the entire second web out.

My rebuild cracked all 3 center webs, but did not affect the crank which by the way was reground (index ground) and nitrided.

Then I added these:

http://www.kennedydiesel.com/images/Splayed-caps-Installed.gif


It now runs about 26psi boost...

[Beedee]

The break was at the back, between #8 and the rear main.
As for the manual tranny thing, I was thinking about it as I was going to work this afternoon, and it makes no sense at all does it, after all, how many tractor trailers are there on the road with automagics in them????
Once again, thanks for the response guys.

26 PSI boost John :D , it will be a while before I'm ready for that tongue.gif

[grape]

Hey John, what do you get for a set of caps and studs? My machine shop will love me for this one.

[Kennedy]

http://www.kennedydiesel.com/detail.cfm?ID=267

[tanker]

Mine broke behind the 2nd main cap. Possible cause was a bad vibration damper, the rubber started to come out. :mad: Other possibilities, but no one knew for sure. Block was also cracked but not sure what happened first. My GM dealer said they see a lot of them in 6.5's. I don't think I've heard of any 6.2's breaking. I hope my new Avant holds up until I can afford a newer rig someday. So far, so good with almost 30,000 miles on it. ;)

[eracers999]

Ive always had a feeling that these things break or crack on start up.
Perfect situation for breaking a block or somthing would be to try to start a 6.5 on a cold morning with 1 or 2 glow plugs not working, it gets just enough raw fuel in the cyl to hydro lock that cyl or real close to it.
So its my belief that a 6.5 needs the glow plug sys kept in real good shape or they will get murdered on start up.
kent