What bends a crank?

[Anonymous-0]

It may be a dumb question but we were talking in the shop the other night and we have heard of engines bending cranks. What causes this to happen and what most time will happen when this happens other than the crank? Just wondering, thanks for any information to learn from.

 

[Pete in MD]

Liquid, water or fuel, in the cylinder that doesn't compress on the compression stroke. Use of ether causing pre-detonation on the compression stroke.

 

[Kent Petersen]

most cranks get bent when a brg gos out

 

[tim s]

A lot of times when a bearing goes out it will create heat and stress, then when you un-bolt it it will sorta "wilt" slightly from being stressed..it may still rotate okay while torqued down in the block, but when you spin it up on a lathe it really shows up, a "small" amount will grind out as you turn it..

 

[Pete in MD]

I can't disagree with you Kent and I don't think you disagree with the causes I listed. But he asked what would cause a bent crank, not what the most common cause was.

 

[Anonymous-0]

I cannot speak from my own experience. Back in 1976, we purchased a 1955 Oliver. It was traded for a 4440 JD in the summer of 1979. We never bent a crankshaft, but we did break a crankshaft in between the 3rd and 4th cylinders. I wish I could say exactly what the cause of it was, but I cannot. What I can say is that we have had some "lemons" on the farm over the years in a variety of colors and brands. This particular tractor was most definitely one of the biggest "lemons" we ever "attempted" to put to work on the farm.

 

[teddy52food]

Back when I was grinding cranks, a bent one had a bearing failure. If it didn't I used the magnaflux & often found it was cracked.

 

[turklilley]

Too much heat is what causes most crankshafts to bend. Can come from bearing falure.

 

[Anonymous-0]

I've never done it but several guys have told me that lugging a motor down to almost stalling it under load can bend a crank or even a rod. Overloading the tractor or even letting the clutch out without revving the motor a little while starting out is not good for a motor. You wouldn't think it would but the crank actually flexes when lugging.

 

[CBL95]

lugging, stalling, out of time, either, if enough is in the cylinder water, fuel, oil, etc. trying to bar the engine over directly if the engine is stuck and a whole host of other things and could possibly maybe happens.