Crankshaft straightening question.

[69427]

Dropped off my new (old stock) Chevy 427 crank at the machine shop yesterday to get it checked out prior to getting the block machinework done. The machinist says that the crank has some runout in the center. We discussed straightening it. I'm interested in additional input here. What's the proper way to nudge it back straight? I've heard conflicting info over the years. Opinions? Recommendations? Experiences?

thanks,
Mike

 

[DWncchs]

If he does straighten it make sure he checks the flywheel mounting flange runout when he's done. (Oh and try and find the flywheel flange runout in a book.)

 

[69427]

If he does straighten it make sure he checks the flywheel mounting flange runout when he's done. (Oh and try and find the flywheel flange runout in a book.)

Damn, good point. I didn't think about that. Thanks, Roger!

 

[DWncchs]

I didn't think about that.

I didn't either and found out the hard way after the engine was back in the car. :bullshit:
The engine builder had the gull to tell me no one checks that flange for runout because that spec is not in any books. Probably no spec in print because its supposed to be .00000000000 #%^&$@#$

 

[pcf_mark]

Be sure they crack check it first, straighten it, then crack check it again. If is cracked now stop - I had a GM steel crank crack from the oil hole to the fillet from a street car.

Once they straighten it, it is likely to crack. If you can put it in the block with oiled bearings and bolts torqued and it turns freely (no seal) I would leave it go for a street car. The GM nitride heat treatment make the cranks more likely to surface crack. I have no experience with the modern LT1/LS1 but the old BBC behaved this way.

 

[69427]

Be sure they crack check it first, straighten it, then crack check it again. If is cracked now stop - I had a GM steel crank crack from the oil hole to the fillet from a street car.

Once they straighten it, it is likely to crack. If you can put it in the block with oiled bearings and bolts torqued and it turns freely (no seal) I would leave it go for a street car. The GM nitride heat treatment make the cranks more likely to surface crack. I have no experience with the modern LT1/LS1 but the old BBC behaved this way.

Yep, we followed that sequence. It's straight now, and no cracks detected.

Given that I've unavoidably ended up putting more money into this engine than I had planned, I've started to get nervous lately. I never worried about the possibility of grenading my current track engine (iron block and factory crank), but this one will hurt the wallet if anything goes south. So, I decided to put this crank on the shelf for now, and I ordered a stronger aftermarket crank. It ought to be here by early next week, and hopefully I can finally get some of the machine work done. (I gotta remember to compare the two crank weights just for amusement, too.)
I'm not discounting the possibility that I could still do something stupid and scatter this engine some weekend, but this way I'll know that I eliminated as many unknowns as I could prior to putting it together. It'll be worth it just to be able to sleep better at night.

 

[TimAT]

What crank did you decide on? I've looked at Eagle, Scat and Callies. Callies looks the best to me in that price range. All Forged 4340 stuff.

 

[1981Z06Vette]

You probably already know this, but store the crank on end...lying flat on a shelf somewhere over the years is probably what bent it in the first place.

 

[mrvette]

You probably already know this, but store the crank on end...lying flat on a shelf somewhere over the years is probably what bent it in the first place.

I have heard that too, makes NO sense to me, but heard it from two different machine shops over the years....

:rain::gurney:

 

[Carb Doc]

You should never leave a crank sitting on the bench or anywhere else, if it is not in the block it should be hung from the Flywheel Flange in a Crank Rack. This goes for Cams as well, hang them up don,t leave them lying around.

 

[big2bird]

You probably already know this, but store the crank on end...lying flat on a shelf somewhere over the years is probably what bent it in the first place.

I have heard that too, makes NO sense to me, but heard it from two different machine shops over the years....

:rain::gurney:

They sag from the unsupported weight. Go in a camgind shop sometime. They are all standing up. Same at National Crank when I was a pup.

 

[SmokinBBC]

Pic from a shop I visited.

 

[69427]

Pic from a shop I visited.

Guys, help me out here. Why wouldn't the crank bend just as easily when being hung like this? It just doesn't look like there is an equal amount of counterweights spread throughout 360 degrees, given that one set of counterweights are above the hanger pins.

 

[SmokinBBC]

Guys, help me out here. Why wouldn't the crank bend just as easily when being hung like this? It just doesn't look like there is an equal amount of counterweights spread throughout 360 degrees, given that one set of counterweights are above the hanger pins.

According to Carb Doc, these are hanging from the wrong end.

 

[Carb Doc]

I believe that the hanging part is more important than which end it hangs from

 

[badbirdcage]

The way you straighten the mains for finish is you grind them straight. That way they are stress free. When you push a crankshaft around in a press to attempt to get it straight you induce stress into the shaft. And yes, the flywheel flange should be machined perpendicular to the mains. You do that with a lathe, aligning on the main bearing surfaces after the shaft is finish ground.

We always used to stand crankshafts on the flywheel end or hang them in a rack from the flywheel end.

Rich:beer:

 

[Carb Doc]

SmokeyYunick addresses the issue of Crankshaft Straightening in his Book " POWER SECRETS", THIS IS NOT SOMETHING THAT HE RECOMMENDS, if you are interested in the details, Page 32 the last paragraph before LUBRICATION.

 

[clutchdust]

Never heard such a thing about cams. Back when I worked for Comp Cams, we had rows and rows of cams in boxes on the shelf. Cranks I see, cams I don't.

 

[big2bird]

The way you straighten the mains for finish is you grind them straight. That way they are stress free. When you push a crankshaft around in a press to attempt to get it straight you induce stress into the shaft. And yes, the flywheel flange should be machined perpendicular to the mains. You do that with a lathe, aligning on the main bearing surfaces after the shaft is finish ground.

We always used to stand crankshafts on the flywheel end or hang them in a rack from the flywheel end.

Rich:beer:

But, it had to be straight when it was ground new. Would you not be just taking the sag out and returning it to the "as new" posture?

 

[Ozzy]

IMHO, they are stored on end as to not take up so much space. Easiest way to store and sort them is on end.
Why hang them versus stand them on end ? So they don't get knocked over and damaged, plain and simple

IF you are worried about "warping" over time, then the only way to store a crank would be to set it in an align bored block

Look at the weights on a crank, when hanging each counterweight is pulling down in with a different tangent.

If you think the crank will bend over time then those tangential angles will be bending the crank in numerous directions.

Has anyone ever taken a precise measurement of the overall length of a crank when laying in a block, then taken the crank out of the block and put it on end, either hanging or standing and remeasured it to see the deflection? I have not but am curious as to how far it does deflect.

just my $.02 worth.