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New crank cracked?

General engine tech -- Drag Racing to Circle Track

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AC sports
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New crank cracked?

Post by AC sports » Wed Apr 10, 2019 6:39 am

Bought a new old stock crankshaft last week for a Fiat twincam.
It arrived with lots of factory wax and a few small areas of surface rust which I polished out. Upon further inspection I find this :
At first I thought maybe a scratch, but given it goes into the fillet radius also, I figure it's a crack.
No one local to x ray, so scrap metal?
Only seen this on used cranks and typically either from oil holes or from fillet radii going out.
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Re: New crank cracked?

Post by BillK » Wed Apr 10, 2019 6:49 am

Where are you located ? No shop in the area that can magnaflux it ?
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Re: New crank cracked?

Post by mag2555 » Wed Apr 10, 2019 6:49 am

It does not look like a crack as it's too jumpy and inconsistent!

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Re: New crank cracked?

Post by enigma57 » Wed Apr 10, 2019 7:19 am

Could be a surface scratch. If you test, do a radiograph. Magnaflux test will pick up discontinuities both open to surface and slightly below surface. Dye penetrant will pick up anything open to surface. Neither will tell you with certainty what is going on deeper beneath the surface.

Or you could turn that journal 0.010" (or until line is no longer visible) and then take another look at it. If its OK, turn remainder of journals same amount.

Just a thought,

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Re: New crank cracked?

Post by Dave Koehler » Wed Apr 10, 2019 8:31 am

Left to right? Never seen a straight line crack. That has to be a scratch. Too straight and it appears to hit the high spots of the machining.
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Re: New crank cracked?

Post by Scotty » Wed Apr 10, 2019 10:42 am

I have seen lots of forged steel diesel and petrol automotive crankshafts that have cracks like that witch line up with the forging line , its certainly worth giving it a polish with fine emery tape and further inspection. You can get a white background paint and magnetic black particle spray cans for crack testing then you only need 2 strong magnets placed either side of the crack to inspect if you cannot get it magnafluxed.
Note the alignment of the crack with the forging line on this crank and usually they are predominatly found on the underside of the be jnl.
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Re: New crank cracked?

Post by Dave Koehler » Wed Apr 10, 2019 11:05 am

Scotty,
Oh yeah, seen those but I think the OPs line looks too straight. Flux will tell of course.
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Re: New crank cracked?

Post by jake197000 » Wed Apr 10, 2019 4:29 pm

look at it under magnification

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Re: New crank cracked?

Post by exhaustgases » Wed Apr 10, 2019 6:11 pm

jake197000 wrote:
Wed Apr 10, 2019 4:29 pm
look at it under magnification
X2

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Re: New crank cracked?

Post by AC sports » Thu Apr 11, 2019 12:22 am

Under 10x it definitely has the jagged lines of a crack and not the smooth edges of a scratch. It doesn't look too deep so may clean up with a 10' turn.

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Re: New crank cracked?

Post by modok » Thu Apr 11, 2019 12:27 am

looks like a scratch, even if it is a crack, I'd guess that it will not cause any problems, because of where it is.
It is possible for a a crank to crack that way during heat treating.

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Re: New crank cracked?

Post by Mummert » Thu Apr 11, 2019 1:04 am

The top doesn't look like a crack. They have very defined skwiggles (if thats a word). The second picture is cracked, but with the small surface cracks around it they may not be that deep. The second crank would probably save with a grind.
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Re: New crank cracked?

Post by bigmike » Thu Apr 11, 2019 4:16 am

That is a forging void.

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Re: New crank cracked?

Post by MotionMachine » Thu Apr 11, 2019 8:21 am

bigmike wrote:
Thu Apr 11, 2019 4:16 am
That is a forging void.
I tend to agree with this. Especially considering it's in line with the forging seam. When I've seen cracks like in the pic Scotty posted, they were caused from heat, just like cracks in the face of a flywheel. I've tried to grind them out but rarely do they go away with a minimal grind. Since the crank is new, it hasn't been subject to any trauma. I think it just didn't clean up completely from the rough forging when it was ground.

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Re: New crank cracked?

Post by Truckedup » Thu Apr 11, 2019 8:26 am

MotionMachine wrote:
Thu Apr 11, 2019 8:21 am
bigmike wrote:
Thu Apr 11, 2019 4:16 am
That is a forging void.
I tend to agree with this. Especially considering it's in line with the forging seam. When I've seen cracks like in the pic Scotty posted, they were caused from heat, just like cracks in the face of a flywheel. I've tried to grind them out but rarely do they go away with a minimal grind. Since the crank is new, it hasn't been subject to any trauma. I think it just didn't clean up completely from the rough forging when it was ground.
If so, is the crank usable for high performance ? Grind it undersize to try and clean it up?
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