broken crankshaft??

[keltalon]

what do you think caused this crankshaft to break like this. by the way it was a remanufactored could it have been vibration of some sort?

oh yeah forgot it came out of my car. maybe remans can't handle 300 plus horsepower

 

[Rabbi]

wow.......


makes me think twice about using my machined 7 bolt crank!

 

[gsx951]

Post a picture of your crank pulley.

 

[bjones18]

Two things:

1. stock harmonic balancer or aftermarket?

2. pic appears to show fracture at the radius of the rear main journal. Check the machined radius (should have a generous radius and cannot be sharp 90 corner) see if there is a crack initiation point.

 

[gsx951]

mine.....

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[forcefed4]

I think a couple of you guys hit it on the nose...

His mod list:

hks 264 in and 264ex cams auto to manual swap! Evo VIII sodium filled ex valves ported and polished head crower spring and retainers ajusa composite head gasket 2g pistons balanced engine under drive pulley no balance shafts

 

[bjones18]

I think a couple of you guys hit it on the nose...
under drive pulley ,,,

Oooo. There is a real good reason engine designers put than think called a harmonic balancer on the front of your crankshaft. And there is a really-really good reason they call it a harmonic balancer and not a pulley. There is also a really greedy excuse for people to make underdrive pullies without two masses separated by an isolater (spring).

Sorry to say, you may have bought your (ud-pulley) crank failure.

 

[keltalon]

Two things:

1. stock harmonic balancer or aftermarket?

2. pic appears to show fracture at the radius of the rear main journal. Check the machined radius (should have a generous radius and cannot be sharp 90 corner) see if there is a crack initiation point.

well the corners are not radius!!

 

[keltalon]

I think a couple of you guys hit it on the nose...

His mod list:

hks 264 in and 264ex cams auto to manual swap! Evo VIII sodium filled ex valves ported and polished head crower spring and retainers ajusa composite head gasket 2g pistons balanced engine under drive pulley no balance shafts

why would it break on the clutch end if it was the underdrive pulley. i have the new crank installed and i am taking no chances i put the stock harmonic balancer back on with a fidanza flywheel.

i found the answer to my own question

Torsional vibration: Every time a cylinder fires, the connecting rod hammers the crankshaft, making it twist as well as spin. After every twist, there's a rebound as the crank unwinds. This twist/rebound cycle is known as torsional vibration and if not controlled, it will result in rapid bearing and crank journal wear and can lead to a broken crankshaft. ( Source: Fluidampr's tech pages. )

Harmonic balancer: The harmonic balancer, or vibration damper, is a device connected to the crankshaft to lessen the torsional vibration. When the cylinders fire, power gets transmitted through the crankshaft. The front of the crankshaft takes the brunt of this power, so it often moves before the rear of the crankshaft. This causes a twisting motion. Then, when the power is removed from the front, the halfway twisted shaft unwinds and snaps back in the opposite direction. Although this unwinding process is quite small, it causes "torsional vibration." To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft that's causing all the trouble. The balancer is made of two pieces connected by rubber plugs, spring loaded friction discs, or both.
When the power from the cylinder hits the front of the crankshaft, it tries to twist the heavy part of the damper, but ends up twisting the rubber or discs connecting the two parts of the damper. The front of the crank can't speed up as much with the damper attached; the force is used to twist the rubber and speed up the damper wheel. This keeps the crankshaft operation calm.
( Source: AutoInsight training program )





Torsional vibration will destroy a crankshaft and/or bearings if left un-dampened.

 

[damnslowtsi]

Has anybody seen a crank that was broken at other than #4 rod journal. Looks like all the pics I 've seen had it at that very spot. Just curious.

 

[Defiant]

Yup.
http://www.dsmtuners.com/forums/showpost.php?p=1513989&postcount=386

 

[keltalon]

Yup.
http://www.dsmtuners.com/forums/showpost.php?p=1513989&postcount=386

WOW!

 

[Jason's TSI]

Several years ago I was having a problem with cranks breaking just like that, I swapped balancers, flywheels, everything I could think of, but after about two months the crank would break again. I replaced the block and never had another problem.