Re: Is it ok to straighten a bent crank
[Re: duckblind]
#1825572
05/13/15 11:12 AM
05/13/15 11:12 AM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
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No problem, very common procedure.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Is it ok to straighten a bent crank
[Re: Supercuda]
#1825640
05/13/15 12:27 PM
05/13/15 12:27 PM
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Joined: Jan 2004
Posts: 9,066 Eugene, Oregon
minivan
master
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master
Joined: Jan 2004
Posts: 9,066
Eugene, Oregon
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No problem, very common procedure. If the crank breaks it will be during the straightening procedure.. Friends Z28 ( 69 - 302) came back in two pieces from the machine shop, back in the day.... An expensive setback when its your High School daily driver..LOL
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Re: Is it ok to straighten a bent crank
[Re: duckblind]
#1825943
05/13/15 06:47 PM
05/13/15 06:47 PM
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Joined: Oct 2005
Posts: 8,882 Ontario, Canada
Stanton
Don't question me!
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Don't question me!
Joined: Oct 2005
Posts: 8,882
Ontario, Canada
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It is a crude process where you put the crank on some V blocks in the hyd press and then you guess at how hard you have to push it. You have to push it past center so it springs back to dead even. Push it too far and it bends the other way. That's why it can take hours to get it dead on. However, breaking a "forged" crank by trying to straighten it is unlikely unless the thing is bent in half!! Cast cranks aren't worth trying and will snap - likely what happened to that chevy crank!
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Re: Is it ok to straighten a bent crank
[Re: duckblind]
#1825949
05/13/15 07:10 PM
05/13/15 07:10 PM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
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Pretty sure a factory Chevy 302 had a forged crank.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Is it ok to straighten a bent crank
[Re: duckblind]
#1826019
05/13/15 08:23 PM
05/13/15 08:23 PM
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Joined: Jan 2011
Posts: 4,785 Utah and Alaska
astjp2
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master
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Utah and Alaska
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Nitriding could cause a crack. ok, let me clarify, straightening a crank that has been nitrided could cause it to crack. Tim
1941 Taylorcraft 1968 Charger 1994 Wrangler 1998 Wrangler 2008 Kia Rio 2017 Jetta
I didn't do 4 years and 9 months of Graduate School to be called Mister!
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Re: Is it ok to straighten a bent crank
[Re: astjp2]
#1826042
05/13/15 08:42 PM
05/13/15 08:42 PM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
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Nitriding could cause a crack. ok, let me clarify, straightening a crank that has been nitrided could cause it to crack. Tim That would explain the 302 crank, they were nitrided.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Is it ok to straighten a bent crank
[Re: Supercuda]
#1828422
05/17/15 12:36 PM
05/17/15 12:36 PM
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Joined: Jan 2004
Posts: 9,066 Eugene, Oregon
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Nitriding could cause a crack. ok, let me clarify, straightening a crank that has been nitrided could cause it to crack. Tim That would explain the 302 crank, they were nitrided. Yes the 302 crank was forged and I believe it had larger journals than the 283.. Remember the 302 was technically a 327 bore with a 283 crank.. Seems as if Chevy was on strike?? when this happened and as said above, this was his "daily" transportation so panic to get it fixed was happening.. NO 302 cranks around so we looked into using a 283 crank.. Wasn't gonna work...
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Re: Is it ok to straighten a bent crank
[Re: duckblind]
#1828425
05/17/15 12:38 PM
05/17/15 12:38 PM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
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Yeah, the 302 used the 283 stroke but the larger journal sizes, and that it way more chevy info than I wanted to know.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Is it ok to straighten a bent crank
[Re: Cab_Burge]
#1828549
05/17/15 03:27 PM
05/17/15 03:27 PM
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Joined: Jan 2004
Posts: 8,295 fredericksburg,va
cudaman1969
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fredericksburg,va
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As probally already mention whne you spin a rod bearing the heat warps the crankshaft, a forged steel crank will bend but it can, and should be be straighten in a press safely before grinding the mains or rod journals I had one 1969 440 crank out of a CA Hiway Patrol car that had spun a rod bearing, I took it to my crankshaft grinding company and watch them try to straighten it in the press before setting it up for grinding, that rascal broke in the middle Far better for it to break in half there than in the motor I always heard when a bearing spins it forms a crack from the heat, got a hemi Kellogg crank with that problem. Better check for cracks, mopar is famous for that.
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Re: Is it ok to straighten a bent crank
[Re: cudaman1969]
#1829403
05/18/15 06:46 PM
05/18/15 06:46 PM
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Joined: Jan 2003
Posts: 16,376
dogdays
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,376
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Magnaflux it, using magnetic particle, not dye penetrant before it is ground, to see if it's worth saving. If it's been ground, dye penetrant should show you any cracks. That goes for any crank.
The overheating CAN cause cracks, really it's probably the uneven cooling that does it, but it doesn't have to. Lots of steel things are forged at red heat or a little hotter, and they don't have cracks. For example look at the Callies ad for its connecting rods where they show you a rod blank during the forging process.
If you can afford it I would strongly suggest getting a 4340 crank, either new or slightly used. It will be 50% or more stronger than the stock crank. I'd hate to waste all the machine work in a block to try to save a buck on the crank.
R.
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Re: Is it ok to straighten a bent crank
[Re: cudaman1969]
#1829453
05/18/15 07:56 PM
05/18/15 07:56 PM
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Joined: Aug 2003
Posts: 43,230 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,230
Bend,OR USA
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As probally already mention whne you spin a rod bearing the heat warps the crankshaft, a forged steel crank will bend but it can, and should be be straighten in a press safely before grinding the mains or rod journals I had one 1969 440 crank out of a CA Hiway Patrol car that had spun a rod bearing, I took it to my crankshaft grinding company and watch them try to straighten it in the press before setting it up for grinding, that rascal broke in the middle Far better for it to break in half there than in the motor I always heard when a bearing spins it forms a crack from the heat, got a hemi Kellogg crank with that problem. Better check for cracks, mopar is famous for that. As already pointed out heat from spinning a bearing can, not always, cause cracks. I have all my rotating parts magged before using them, I have had some cranks with cracks in the fillets ground out and welded up and then repaired In fact I have a old forged steel Bryant 4.5 stroke top fuel carnk with the center counterweights that is cracked in multiple places, I've got a bid of $800.00 to have it welded and repaired so it is uaseable in a street or mild bracket race motor.That crank has never spun a bearing that I can see any evidence of or the crank repair specialitis could see or tell of A new one like it starts at $3200.00 now so maybe I will have it fixed and use it
Last edited by Cab_Burge; 05/18/15 07:57 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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