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Old 12-10-2007, 06:05 AM
83elky's Avatar
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How to tell if my crank is forged or not?

I just bought a 383 package for 300$ It has a gm crank, .30 over trw aluminum forged flat top pistons and not sure of the rods yet was told they are 585 rods? My question is how do you tell If the crank is cast,forged or steel? On a chevy 400 2 pc rear main crank. I think it's a 1969 block any help would be appreciated

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Last edited by 83elky; 12-10-2007 at 06:45 AM.
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Old 12-10-2007, 06:39 AM
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The parting line on the front weight should be about an inch wide if it's forged. A cast crank will have a thin line.
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Old 12-10-2007, 09:00 AM
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I've put two pic.s up here, you can see the forging line and the cast line (I've circled both in the pic.). the cast pic is pretty good representation, the forged pic. is the best I could find, and it's not a pretty pic. for obvious reasons!


Forged crank (see wide trim line)


Cast crank (see thin casting line)

Hope these help, Good Luck!
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Old 12-10-2007, 10:05 AM
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Those forged cranks must have that weak point.I have one that cracked just like first pic
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Old 12-10-2007, 12:55 PM
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Gorilla glue!
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Old 12-10-2007, 01:41 PM
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Quote:
Originally Posted by 11echo
I've put two pic.s up here, you can see the forging line and the cast line (I've circled both in the pic.). the cast pic is pretty good representation, the forged pic. is the best I could find, and it's not a pretty pic. for obvious reasons!


Forged crank (see wide trim line)


Cast crank (see thin casting line)

Hope these help, Good Luck!
Wow. That first crank needs some duct tape!!

Mark.
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Old 12-10-2007, 02:23 PM
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Is there a casting number on the crankshaft? If that 400 crank is a factory crankshaft there should be casting numbers on it. If you go to www.mortec.com you can look up the crankshaft casting numbers. More than likely it's a cast crank, especially given how much you paid for the setup.
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Old 12-10-2007, 06:14 PM
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So, Is this proof that a forged crank is not as good as a cast?
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Old 12-10-2007, 07:03 PM
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No, it just proves that 11echo is good at breaking cranks

Forged is almost always stronger than cast. Cast is a bit brittle; strong, but doesn't respond well to really high shock loads like high output engines can make.
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Old 12-11-2007, 08:02 AM
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Hey "I DIDN'T DO IT!" ...as I said this was the best pic I could find! but it does point out NOTHING is "bullet proof"!
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Old 12-11-2007, 10:03 AM
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Pulled the oil pan off today and come to find out it's a aftermarket scat forged crank. So i got a pretty good deal so far, but We'll see when it comes back from the machine shop. Thanks everybody for the help! If my crank has a crack in it like the forged pic one has IS THAT BAD? lol j\k sucks to be that guy! Thanks again
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Old 12-11-2007, 11:35 AM
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One thing! ...Be sure to have that crank crack tested!!! ...They soak it in a dye penetrating solution to check (I forget the name of this test!!?? anybody?? ...help an old guy out?? *L*) ...One time I had bought a 454 steel crank in a swap meet. It looked good but thought I'd check anyway, turned out to be a bad crank!! Save me alot of money!!!
MAGDAFLUXED!!! That's what it's called!! (Gawd I hate getting old!! *G* )

Last edited by 11echo; 12-11-2007 at 11:41 AM.
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Old 12-11-2007, 12:44 PM
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Quote:
Gorilla glue!... duct tape...
Ain'ch y'all heerd a J-B Weld!?

Quote:
Is this proof that a forged crank is not as good as a cast
NO NO NO This has nothing to do with proving anything. Any crank can be broken - any, cast, nodular, 5140, 4340, even billet. And, they break for many different reasons. Sometimes its fatigue. So, after X million cycles, even if it mags good, rings good, when it's life is over its over.
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