Author Topic: Crank Shaft Runout  (Read 2577 times)

Offline jmccrack

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Crank Shaft Runout
« on: August 09, 2015, 01:19:51 AM »
Hey Guys.
Just wondering when I run a dial in the area you see in the picture I get .0015" runout. I know it should be "0" thoughts??

Offline b.lindsey

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Re: Crank Shaft Runout
« Reply #1 on: August 09, 2015, 01:28:41 AM »
Is the diameter you are measuring machined or is the crankshaft built up from something like drill rod? As long as it is running fine in the bearings and not binding, you should be ok. Just my 2 cents.

Bill

Offline derekwarner

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Re: Crank Shaft Runout
« Reply #2 on: August 09, 2015, 02:47:40 AM »
If you think about the 1 1/2 thou run out, it may be a bend in the journal landing it self ...really has little to do with being a part of the crank shaft assembly as you are measuring a shaft that is contained in the bearing bush

What is the clearance between the bush & the journal section?.......you need not measure these components, just try & gauge deflection on the indicator

If you move the indicator pointer closer to the web, does the run out decrease?.........

What is the reading on the opposite journal?.......... Derek
« Last Edit: August 09, 2015, 06:41:24 AM by derekwarner_decoy »
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Offline philjoe5

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Re: Crank Shaft Runout
« Reply #3 on: August 09, 2015, 04:19:14 AM »
Quote
I know it should be "0" thoughts
Runout of 0.0015" doesn't seem excessive to me.  I think the ideal of "0" is seldom achieved.  If your crank rotates smoothly then you should have a winner.

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline Art K

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Re: Crank Shaft Runout
« Reply #4 on: August 09, 2015, 06:03:27 AM »
Phil,
I wouldn't think that would be a problem unless it binds while rotating. I must admit I've never checked the runout on my Upshur and it'll turn 7000 rpm.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Online Roger B

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Re: Crank Shaft Runout
« Reply #5 on: August 09, 2015, 07:18:21 AM »
As the others have said if it runs freely it should not be a problem. Is the crankshaft just pinned or have you silver soldered or Loctited? Heat can result in residual stresses and distortion.

If it still concerns you you need to make some more measurements as Derek says. Another option is to mount the crankshaft in a collet in your lathe and make the measurements there. That way you can see if the mainshafts are splayed or parallel but not in line. If appropriate a careful tweak to correct the alignment may be possible.

The crankshaft in the picture was machined from cold rolled steel which tends to have a lot of residual stress.
Best regards

Roger

Offline jmccrack

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Re: Crank Shaft Runout
« Reply #6 on: August 09, 2015, 04:47:17 PM »
Thanks Guys
I think by its very nature a crankshaft needs support. On a single throw like this one the if the free ends were not supported in the bearings there would be a lot of runout. When I put one free end in a collet and do not support the other with a centre I have about .010" runout which I can bend back in place very easy.As soon as I bring up the centre support it runs within .0005". When I put the bearings in place I have .0015' runout (with no oil) I have .001" clearance in the bearing. Great information thanks. This my second engine and my first crank.

 

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