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Bent crankshaft causes and myths

Posted By: fourgearsavoy

Bent crankshaft causes and myths - 01/12/14 10:28 PM

Has anybody ever seen first-hand a crank bend from laying in a box on a shelf? Now to me it seems physically impossible that something that is built so strong can bend under it's own weight.Now if this were true how could you possibly ship one
I'm building a Chevy small block for my father-in-laws Vette and one his "buddies" tried to tell me not to use the crank he has becuse it's bent because it's been laying on a shelf for too long.
Now if this is true how long does it take for a crank to bend under it's own weight? One week, one hour, a year
Now most of us have purchased a brand new crank and it comes in a box that has probably been on a shelf for a while so are they all bent?
Gus

Attached picture 7995091-savoyburnout.jpg
Posted By: 71yelladustr

Re: Bent crankshaft causes and myths - 01/12/14 11:34 PM

Those guys probably believe in unicorns too. If you are concerned about it why not just check it? I would think if you installed only the #1 and #5 upper main bearings in the block, then layed the crank in the bearings, and slowly spun it with a dial indicator on the #3 main journal it would show any signs of a bend. Correct??
Posted By: 67_Satellite

Re: Bent crankshaft causes and myths - 01/12/14 11:39 PM

I'd rather let it lie flat for years than stand it on end and knock it over once.
Posted By: MR_P_BODY

Re: Bent crankshaft causes and myths - 01/12/14 11:40 PM

Quote:

Has anybody ever seen first-hand a crank bend from laying in a box on a shelf? Now to me it seems physically impossible that something that is built so strong can bend under it's own weight.Now if this were true how could you possibly ship one
I'm building a Chevy small block for my father-in-laws Vette and one his "buddies" tried to tell me not to use the crank he has becuse it's bent because it's been laying on a shelf for too long.
Now if this is true how long does it take for a crank to bend under it's own weight? One week, one hour, a year
Now most of us have purchased a brand new crank and it comes in a box that has probably been on a shelf for a while so are they all bent?
Gus



To me if they bend that easy you dont want it.. but
most crank shops hang them from the back flange BUT
thats to save space in the shop... the one shop I
use to deal with I asked them this myth and thats
all it was.. a myth unless you put a few hundred pounds
on it for a LONG time... its easy enough to check
with V-blocks or on the lathe
Posted By: drew72

Re: Bent crankshaft causes and myths - 01/13/14 12:26 AM

And batteries will discharge sitting on concrete.
Posted By: moparts

Re: Bent crankshaft causes and myths - 01/13/14 12:37 AM

Quote:

And batteries will discharge sitting on concrete.



But the old tar top batteries will ( Pre 70's ), not the plastic case ones
Posted By: Cab_Burge

Re: Bent crankshaft causes and myths - 01/13/14 02:24 AM

I've had several 318 forged steel cranks out of OEM production motors that had the #2 main bent(checking it with a set of V blocks and a dial indicator) .0007 that was just enough to make those cranks kave a tight spot when spinning it without any rods or pistons in the motor. I have heard the same thing on laying cranks down, they will bend Maybe a cast iron crank will I also have several smashed toes from bumping into a crank standing up and it falling forward onto my foot I have several new foregded steel stroker cranks in thier shipping boxes laying on my shelfs in the shop, I have never seen or heard of or had a forged steel crank be bent if it had not spun a rod bearing or suffered some other form of abuse first
Posted By: moparman89

Re: Bent crankshaft causes and myths - 01/13/14 02:46 AM

Cant believe this is even a thread. If a crank will bend under its own weigh how would it ever hold up to the stresses of a engine?
Posted By: dakotawilly

Re: Bent crankshaft causes and myths - 01/13/14 02:49 AM

Chinese cranks are a crapshoot,their idea of runout is when the cat gets away from the butcher block.plus I am quite sure the average employee at the bingdong crankshaft factory cant read.....hence the occasional blem sales from most of the crank distributors.....
Posted By: Twostick

Re: Bent crankshaft causes and myths - 01/13/14 08:59 AM

Define bent.

.00000x I'm sure could happen by putting it in a hot sunny window that only heated one side. If it was stored on its side and only supported by the end mains I'm sure there is also measurable deflection but I doubt there are many people with the instruments to accurately measure it.

Kevin
Posted By: GTX MATT

Re: Bent crankshaft causes and myths - 01/13/14 09:56 AM

Quote:

Chinese cranks are a crapshoot,their idea of runout is when the cat gets away from the butcher block.plus I am quite sure the average employee at the bingdong crankshaft factory cant read.....hence the occasional blem sales from most of the crank distributors.....



Posted By: sshemi

Re: Bent crankshaft causes and myths - 01/13/14 09:16 PM

This is stupid.

If it gets bent when laying down it should get longer when hung and shorter when standing.
Again its just stupid.
Posted By: Mopar Sam

Re: Bent crankshaft causes and myths - 01/13/14 11:21 PM

It lays flat in the motor.
Posted By: Guitar Jones

Re: Bent crankshaft causes and myths - 01/13/14 11:22 PM

Quote:

This is stupid.

If it gets bent when laying down it should get longer when hung and shorter when standing.
Again its just stupid.



Man I've been doing it wrong!
Posted By: cudaman1969

Re: Bent crankshaft causes and myths - 01/14/14 01:17 AM

Not a crank but something along the same line are the propeller shaft in navy ships. Some are 200 feet long or more and 36-48 inches in diameter. When docked they turn them very slowly to keep from bending. If they have to work on any part of the shaft they put blocks every so many feet for support, they will bend if not done.If it bends it's remachined where it rides, quite a process since it can't be removed from ship
Posted By: MR_P_BODY

Re: Bent crankshaft causes and myths - 01/14/14 01:28 AM

Quote:

Not a crank but something along the same line are the propeller shaft in navy ships. Some are 200 feet long or more and 36-48 inches in diameter. When docked they turn them very slowly to keep from bending. If they have to work on any part of the shaft they put blocks every so many feet for support, they will bend if not done.If it bends it's remachined where it rides, quite a process since it can't be removed from ship



I've never seen one that long but the 1000' ships
here shut down and nothing is turning... I never
turned my shafts even over the winter on my barge
Posted By: cudaman1969

Re: Bent crankshaft causes and myths - 01/14/14 01:57 AM

Shafts must be short, USS North Carolina are that size, and this was first hand knowledge from two engine room guys from a carrier during WW2. They had a lathe that road a cradle with the man riding for the full length.
Posted By: dakotawilly

Re: Bent crankshaft causes and myths - 01/14/14 02:11 AM

I suppose anything could bend under the right conditions,how about the friendly delivery guy tossing it during shipping,you know the old saying,"hey yall watch this"................
Posted By: dOrk !

Re: Bent crankshaft causes and myths - 01/14/14 02:12 AM

Quote:

Has anybody ever seen first-hand a crank bend from laying in a box on a shelf?





WITH the major weather TEMP CHANGES in Ohio ...I have heard a CRANKy person can get bent-outa-shape just thinking about the great tropical temps in Florida ....

What say YOU ?
Posted By: dakotawilly

Re: Bent crankshaft causes and myths - 01/14/14 02:33 AM

absolutely!!!!!if you don't like the weather in ohio,stick around 5 min it will change.....
Posted By: dOrk !

Re: Bent crankshaft causes and myths - 01/14/14 02:39 AM

Quote:

absolutely!!!!!if you don't like the weather in ohio,stick around 5 min it will change.....



Yeah dw ... big changes here toooo ... the swing 2day was 79 the high ....66 the low ....

....a little windy in the Gulf ... with 4 foot rollers ... but PURRfect for some 80mph shots !
Posted By: MR_P_BODY

Re: Bent crankshaft causes and myths - 01/14/14 02:42 AM

Wasnt bad up here today.. was 46*.. its still 42* now
Posted By: CHAPPER

Re: Bent crankshaft causes and myths - 01/14/14 04:55 AM

I have found that my crank bends easily, no matter how you store it.
I believe it has more to do with age than lack of proper care/storage.
Posted By: dOrk !

Re: Bent crankshaft causes and myths - 01/14/14 04:57 AM

Quote:

I have found that my crank bends easily, no matter how you store it.
I believe it has more to do with age than lack of proper care/storage.



A BENT CRANK and rusty-nuts ....

TELL THAT to Dr Phil ...
Posted By: VernMotor

Re: Bent crankshaft causes and myths - 01/14/14 05:01 AM

Swollen Rusty Nuts
Posted By: d-150

Re: Bent crankshaft causes and myths - 01/14/14 05:02 AM

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