Crank failure

General engine tech -- Drag Racing to Circle Track

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dwilliams
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Re: Crank failure

Post by dwilliams »

That's where 50oz 5.0s like to break. For the record, I've never seen a 28oz 302 break there.

I've never seen *any* 351W crank break there, though. What balancer were you running?
Steve.k
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Re: Crank failure

Post by Steve.k »

That is a Windsor crank to fit it 400 ford. Romac balancer. But the one that spun was professional products which i hear not that great.
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Re: Crank failure

Post by Steve.k »

IMG_4030.JPG
IMG_4029.JPG
. Well boys after further inspection i made the mistake. No fault of rpm or balancer. Can you see from pic what i did on #1. Thats a different rod of course. I did talk to the builder i bought Rod's from he skeptical he thinks enough bevel each way? Thats the only thing i can find in whole engine.
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Steve.k
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Re: Crank failure

Post by Steve.k »

Not looking like rod issue. They are specifically beveled each way. Does not matter the direction.
Dan Timberlake
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Re: Crank failure

Post by Dan Timberlake »

Good closeups of the fracture surface would likely be useful.

I'm suspecting the crack started at a geometric or material defect in the rod journal radius/fillet.
Steve.k
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Re: Crank failure

Post by Steve.k »

IMG_4045.JPG
IMG_4047.JPG
IMG_4020.JPG
are these better.
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Kevin Johnson
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Re: Crank failure

Post by Kevin Johnson »

Steve.k wrote: Mon Aug 19, 2019 11:55 am Any specific reason why crank would break in front of front main? 700hp na? Forged Steel.? 438 inch sbf.
Sorry that I misunderstood the break location: in front of the front rod journal; behind the front main.

Thanks for the pics.
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Steve.k
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Re: Crank failure

Post by Steve.k »

300-400 passes. Likely to end of cylce time.
Dan Timberlake
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Re: Crank failure

Post by Dan Timberlake »

The radius on the other end of the rod journal //looks// nicely formed and finished.

On the next crank I'd go easier on the web/cheek thinning and especially the size of the lightening hole.
If I'm looking at the pictures correctly the finish of the lightening hole is kind of ragged.
download/file.php?id=22361&mode=view

Straight on pictures of the actual fracture faces might help understand how important that was.

================.

I'd say the crack(s) had a wonderful time initiating and propagating around the fillet/radius.
download/file.php?id=22359&mode=view

Dye pen LPT of the radius with the pan off and one rod cap removed would have caught them in the act many passes before the final failure.
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Re: Crank failure

Post by Steve.k »

Thanks Dan. I'll get you some better shots tonight. So you thinking cycle time and normal fatigue basically ?
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Re: Crank failure

Post by ClassAct »

Steve.k wrote: Sun Aug 25, 2019 12:26 pm Thanks Dan. I'll get you some better shots tonight. So you thinking cycle time and normal fatigue basically ?
No way is that cycle time. That is a junk damper, like I said way back. Seen it before. A junk damper will break any crank. Morose should have been sued and bankrupted when they released that idiotic solid aluminum hub to the pubic. Bet I've seen a dozen (maybe more) cranks killed by that one junk part.

That's a bad damper. Whether it was junk to start with, or just ended up junk I can't say. But your damper did that. I personally have abused stock cranks way more than that and never broke one like that.
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Re: Crank failure

Post by Steve.k »

I've never broke a stock crank ever and also ran alot more than this. So you are saying the professional products damper that spun a few years ago started this?
ClassAct
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Re: Crank failure

Post by ClassAct »

Steve.k wrote: Sun Aug 25, 2019 6:03 pm I've never broke a stock crank ever and also ran alot more than this. So you are saying the professional products damper that spun a few years ago started this?


I'm saying that's what a crank looks like when the damper isn't doing the job. Don't care what name was on it.
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Re: Crank failure

Post by Steve.k »

Well it could be. Thats the answers im looking for. The second damper romac are a good name damper. But not saying it couldn't be defective.
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Re: Crank failure

Post by Joe-71 »

Do any of the other crank journals show signs of blueing where the rods have been against the cheek of the throw? That blueing seems to be a sign of too little rod side clearance. Maybe it is the pictures, but it sure looks suspicious. Be interesting to measure those two rod big ends together and see just how much clearance you actually had. Joe-JDC
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