83 6.2 Busted Crank

[spitfirenut]

Well, I finally got a chance to pull the front of the engine apart on my truck that I developed a noise in last October. I haven't pulled the pan yet, but the way the snout of the crank can move up, down, side to side and front to back is a pretty good indication that it broke. The angle changes to much for a 3 foot long piece of steel in bearings and the flexplate doesen't move back and forth when The snout moves in and out 1/16". Anyway, the balancer looks perfect. My question is this, does anybody know the relationship of the keyway to the slot on the outer ring that goes across the outer edge of the rim (kind of like a saw kerf)? Mine has the keyway and the slot separated by about an inch. I won't be reusing the balancer, I'm just trying to get a handle on why it broke. I'm wondering if the outer ring slipped causing it to lose effectiveness. At the time of failure I was towing a 12' utility trailer empty and had just completed a 600 mile round trip. My gear code is GO8 which is standard rear end ratio(3.08?) so even in 3rd gear could I have been lugging some and creating problems. I usually run in 3rd around town because the transmisson shifts between 3 & 4 real often under 45. I'm leaning toward a used engine from Diesel Depot at the moment, but I want to prevent this from happening again. BTW mileage was approximately 250k when it happened. Thoughts anyone? Thanks,

[john8662]

So you're saying that you removed the harmonic balancer and it had turned 1" on the crank because of a failed woodruf key?

If so, that could sure cause the crank to break. How tight was the bolt on the crank before the balancer was removed? It's supposed to be 200 ft./lbs. So it's fun removing.

[spitfirenut]

No, the mark on the ring outside the rubber is not lined up with the keyway. Should it be? I'm just trying to get an idea why a perfectly running albeit relatively high mileage engine would break the crank with the original balancer appearing to be in perfect condition. I've run into props on boats that can separate from the rubber and look perfect, but slipping and was wondering if that could happen with a balancer. Another possibility that exists is that it was running the original timing chain. No way of telling how much slop though as the front main ate it when the crank failed.
Don
Well, I just looked at a picture of one on ebay and the slot ant the keyway are in the same relationship to one another as mine. Oh well. Maybe the timing chain stretch?

[ 05-13-2005, 02:20 PM: Message edited by: spitfirenut ]