broken crank and harmonic balancer ??

[92gmc]

this is a spin off from the "bad things happen when 6.5 miss" thread.

How many of you have experienced a broken crank and determined that the harmonic balancer had failed and (presumably) caused the crank failure ?

IMO, as Mark Rinker alluded to, rough running due to injection problems or a weak cylinder may have more to do with a crank breaking than harmonic balancer condition.

My 87 that broke a crank was a very strong and smooth high mile engine. Not really much towing or heavy hauling, the only notable hard thing on that engine was a lot of cold starts in sub-zero.

comments ??

[450]

Do you know if you had the block web cracks prior to the broken crank?...My 6.2 snapped its crank and ripped the bottom end out, it hammered seconds prior to sudden stop...it was high milage but the balancer looked good...it ripped the block webs out along the same lines as where the web cracks would be...I would guess the cracks were there before but can't say for sure...it also ripped a rod out of the piston...too much damage to say what came first, although it looked like the piston came down and met a crank throw.

[Diesel Dan]

I pulled down a low mileage 6.2 and high mileage 6.5 and both had cracked blocks. Both good balancers, no broken cranks. The 6.5 did spin 2 rod bearings. One auto, one manual. Cracks were only .5-.75" long at main web outter bolt hole.