so cruising down the street oing from 4th to 5th. i press the clutct pedal and really weird knocking/ vibrating noise comes out. pull over and check it. it seemed like tranny. go ack on the highway to go home and sounded like a clutch, get home now it sound like a motor, we pull the tranny out and inspect it and it seems fine clutch seems fine. pull the pan and come to find this. what would cause it, wasnt reving it or anything just cruising. its a 2.4 100mm crank. its from the clutch side.

 

Great googly moogly! WTF? Any further info gleaned from the motor autopsy?

 

How olds the build and what brand crank?

 

It looks like a torsional fatigue stress fracture originating at the root of the radius between pin and web. It was caused by torsional vibration, and probably started at a stress concentration caused by a piece of slag, or a forging defect, right at the surface of the pin where it meets the web. Unfortunately this happens in the life of Evo!


Time for a rebuild. What are you going for next?

 

Surprisingly the journal was unharmed. The engine is about 6 month old. The rods were unharmed. So I got a new Manley forged crank and a new set of acl bearings. Gonna send the crank with clutch and it's component's to get balanced togethe . I am keeping the same setup since it didn't harm anything. And go back and shoot for more power.

 

Out of curiosity are the 2.4 cranks forged like the OEM 2.0's? Rarely hear about crank failures on the stock 4G63.

 

ive always heard the 4g64 OEM cranks were about 1/2 as strong as the 4G63 cranks.

You got to think... those 4G64 cranks were all in sedans... and in general, slow cars.

The 4G63 cranks were in evo's, which meant the engineers payed a little more attention to the crank strength.

 

4g63 cranks are much better than 4g64. But then I'll be 2.1 lt. Instead of 2.4lt

 

Bad hit! Glad to see nothing else was harmed! Hopefully your new crank will give you some better luck

 

Dynamically balancing the crank with flywheel and clutch only addresses part of the problem - primary balance. I'm guessing you were running the 4g64 crank without the balance shafts right? If so, consider using a fluidampr crankshaft pulley (http://www.fluidampr.com/product/610701/) in the rebuild to reduce harmonic torsional vibrations that will rapidly fatigue the journal/web next to the flywheel.

 

This would be the first 4g64 crank I've seen anyone break What power were you making before it died?

 

the car has made 700+ before.

 

yea i had no balance shafts. but what bothers is motor ran fine on the old 700 setup. we just refreshened couple things up and threw a smalled turbo and this happened. sucks. but yea the forged crank is here just waiting on the fluidampr

 

I was going to ask about whether or not you had balance shafts. Does this mean it's better to keep the balance shafts? Or would a Fluidampr make up for what is lost with balance shafts? Generally curious about it as I'm contemplating a 4g64 build at some point.

 

I'm pretty sure English said something about the 100mm cranks being horrible. "Horrible" is a relative term, but they just never had great luck with that. That or I'm completely backwards and the 100mm were perfect. But I'm pretty sure not...