what would cause this failure of a crank?

Saw this on the CJ2A Page. What would cause a crank to fail like this?

Over revving,then piston hitting the valve??

I will vote lack of oil pressure.

Over-rev and or Over-torque(rev it up and dump the clutch). Better sideline all jeeps and get an analysis done at the Swiss Metals Lab.


It's amazing that a crank would break with numbers like these, Horsepower (actual @ 4,000 RPM)................60
Torque (max. @ 2,000 RPM).........................105 Lbs. Ft.

Mis-alignment.
Check shaft alignment, then check crankshaft deflection.
Verify with allowables of engine specs.

Over reving and over torqueing? Lack of oil/oil pressure?

Lots of possibilities. Do they have any other pics?

Of particular concern are what appear to be circular gouges in the un-machined face of the crank. This is obviously not intended to be a wear surface, and yet appears to have been subjected to some pretty harsh wear. Did something allow or cause a lateral force on the crank, rather than the circular motion it is designed for??

WW2Chevy said:

Of particular concern are what appear to be circular gouges in the un-machined face of the crank. This is obviously not intended to be a wear surface, and yet appears to have been subjected to some pretty harsh wear. Did something allow or cause a lateral force on the crank, rather than the circular motion it is designed for??

Click to expand...

Pogostick?

kcimb said:

WW2Chevy said:

Of particular concern are what appear to be circular gouges in the un-machined face of the crank. This is obviously not intended to be a wear surface, and yet appears to have been subjected to some pretty harsh wear. Did something allow or cause a lateral force on the crank, rather than the circular motion it is designed for??

Click to expand...

Pogostick?

Click to expand...

Huh!?!

WW2Chevy said:

kcimb said:

WW2Chevy said:

Of particular concern are what appear to be circular gouges in the un-machined face of the crank. This is obviously not intended to be a wear surface, and yet appears to have been subjected to some pretty harsh wear. Did something allow or cause a lateral force on the crank, rather than the circular motion it is designed for??

Click to expand...

Pogostick?

Click to expand...

Huh!?!

Click to expand...

Perhaps someone was using it as a pogostick.

I think the circular marks are from when it broke, and was rubbing against the other part of the crankshaft.

The pogo comment was a complete waste of space.

It more than likely Over rev, and possibly OUT of Ballance{Loose Flywheel}

Could just be metal fatigue. We had a farm tractor break a crankshaft in half during startup once. It was just a little 4 cylinder gas engine with 65 hp. Of course, Murphy's Law was in effect during the break......we had a hay barn catch fire and this was the tractor with the loader on it that we needed to unload the barn.

Fording problem maybe.

I had a 1964 Impalla SS 327 2 speed auto trans. I was driving down the road around 65 mph and accidently bumped the shifter into low. It cracked one of the counter weights on the crank and dang near tore it off.
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Usually, if the crank breaks behind the #1 main it is a vibration damper issue....if the break is in front of the last main journal, be it a 4, 6, V6, V8, etc, it usually indicates a problem at the rear of the engine, like a flywheel/clutch issue.

Pattern of gouging appears to continue across fractured surface. If the gouging occured first then it's sharp, rough edges could have created stress risers.
Better shots of the fracture surface would help. If one area shows a darker tinge then it may have been cracked for some time and at some point just failed across the rest of the crank throw. A shock like dumping the clutch will put far higher loads on a part than high but constant torque.
Sheared vs. snapped vs. cracked surfaces each have their own distinctive "look". A little close-up study would probably reveal some tell-tale signs.