Just trying to learn from this crankshaft failure. The crank is a Eagle 4.25 - 2.75 main which has been in my bracket car since 2007 (yes 18 years) and I estimate about 4K 1/8 mile passes. The engine is a 351W bored and stroked to 460 cid. The max rpm I shift at is 6400 rpm with a two speed PG and the balancer is a ATI super balancer. If you zoom into the picture you can see cracks in the corner of the timing chain gear key way. The crankshaft snout drives an alternator and vacuum pump only. No warning when it suddenly let go at the finish line. Why did it fail? Why would there be cracks at the key way feature? Any help would be appreciated. Note: not sure how to attach my photos?

Tim

This message has been edited. Last edited by: thehueypilot,

4k 1/8 mile passes…that thing should be in a museum, especially for an eagle

Is the crank gear cracked on the backside? (Closest to the block)

No the timing gear is in good shape and the crank failure happened right under the gear as it is barely holding onto the crankshaft. I got lucky the gear did not fail/fall off and take the engine out.

Tim

quote:

picture you can see cracks in the corner of the timing chain gear key way

Front or back of the gear?

The cracks in the key way are to the front of the timing gear. One thing I am going to change is the amount of length the balancer sticks out from the end of the crankshaft. The difference between a late model and early model car is about one inch more of length (maybe the width difference of the serpentine belt vs the v-belt). I purchased the early model balancer which should move the balancer and pulleys weight in toward the center of the crankshaft which hopefully takes away some stress from the failed area? Any thoughts?

Tim

PS thanks to Ken Harris for the helpful info!

This message has been edited. Last edited by: thehueypilot,

You honestly should be making a post thanking eagle. It broke because you pushed it past its intended use by 2000 passes.

That crankshaft owes you nothing, Just gotta hope your next one last that long

This message has been edited. Last edited by: Big Steve,

quote:

Originally posted by Big Steve:
Thank crankshaft owes you nothing, Just gotta hope your next one last that long

This 1000%

Yeah, you got 4000 passes out of a Chinese crank.... I'd say you are way ahead of the game.

Years ago It was shown that multiple position keyway timing gears caused stress risers in crankshaft snouts.

If you`re going to buy anther "cheap" crank, look into Scat. There cranks have come a long way and mic up very nice. I got away from the Eagle cranks.

No answers for you, but a good while back I saw a broken crank on a diesel engine on a diesel-electric drilling rig. The engine was still running and the balancer was wobbling like crazy. This is only to say it sounds like a similar failure.

When assembled did you check the alignment of the timing gears before installing the chain?

Stress risers generated by intermittent bore contact may result in crankshaft failure. This is from even Callies. Aside from that stay away from the 9 slot setup. You will never need it. If your for real on the 15 years and 4k hits. I think and end table will be in order.

quote:

Originally posted by Bad News:
Years ago It was shown that multiple position keyway timing gears caused stress risers in crankshaft snouts.

This. ^^^^^^


What vibration dampner you running?

Easy answer is LS swap.....

quote:

Originally posted by Eman:
When assembled did you check the alignment of the timing gears before installing the chain?

Yes the gears were checked for alignment during the initial install. The timing gears/chain were in good shape but I will replace them. I have not heard of the multi key way gear causing stress risers but it did fail right under the gear. I guess I got lucky the gear held onto what was left of the crank snout.

Tim

quote:

Originally posted by Goob:

quote:

Originally posted by Bad News:
Years ago It was shown that multiple position keyway timing gears caused stress risers in crankshaft snouts.

This. ^^^^^^


What vibration dampner you running?

Easy answer is LS swap.....

ATI super balancer with the late model four bolt set up. I am switching to their three bolt balancer which is about 1/2” shorter.

Tim

This message has been edited. Last edited by: thehueypilot,

IIRC, the multi-keyway gears didn't have enough bevel on the engine side and were actually cutting into the crank when driven on fully.

Don't run the blower belt so tight.