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Author Topic: Crank Straightness Tolerance  (Read 6448 times)

rjcroc

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Crank Straightness Tolerance
« on: August 19, 2006, 03:12:03 PM »

Hello to all,

I am trying to straighten my crankshaft and want to know what tolerance is acceptable. Before welding I had .002 TIR now I am at .010 and need to know what I need to straighten the crank to. Is the origional .002 even in spec.?
Thanks for any info

Rick
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mobile_bob

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Re: Crank Straightness Tolerance
« Reply #1 on: August 19, 2006, 03:15:46 PM »
not sure of the spec, but am curious

why did you need to weld the crankshaft?

bob g
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rjcroc

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Re: Crank Straightness Tolerance
« Reply #2 on: August 19, 2006, 03:31:03 PM »

Gib keys, need I saw more?
Drilled them out after weeks of kroil,Jameson,Baileys,miller lite, not to mention a little agrivation.

Rick
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"THE GREATEST DANGER FOR MOST OF US IS NOT THAT OUR AIM IS TOO HIGH AND WE MISS IT, BUT THAT IT IS TOO LOW AND WE REACH IT"  MICHELANGELO
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GuyFawkes

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Re: Crank Straightness Tolerance
« Reply #3 on: August 19, 2006, 04:06:45 PM »
Quote from: rjcroc on August 19, 2006, 03:12:03 PM

Hello to all,

I am trying to straighten my crankshaft and want to know what tolerance is acceptable. Before welding I had .002 TIR now I am at .010 and need to know what I need to straighten the crank to. Is the origional .002 even in spec.?
Thanks for any info

Rick

Half a thou was the "known" limit, eg 0.0005 inch***

*** known as in I've had to do this twice _ever_ to cranks that had suffered some damage (both wrapped up a belt and stalled out) , and this was the number given to me by a Lister tech many moons ago, in both cases the whole crank was heat treated before and after, it was a loooong job, if a replacement crank had been available we'd have done it that way.

remember this was original lister with the bushed mains, we took a great deal of care getting the flywheels running true and square, last thing we wanted was buggering up the flywheels and having to bush them...
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rjcroc

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Re: Crank Straightness Tolerance
« Reply #4 on: August 19, 2006, 04:26:32 PM »

Guy, thanks for the info. Where did you measure the .0005? Even with the crank on rollers at the bearing mounting location I only measured .002 but I also checked at the ends of the shaft and also got .002 so I thought the crank was relativly straight. Now I still get .002 near the bearing mount and .010 at the end. Did you mechanically straighten or use spot heat to straighten? Thanks again. Im going to make this basterd into a silk purse if it kills me.

Rick
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"THE GREATEST DANGER FOR MOST OF US IS NOT THAT OUR AIM IS TOO HIGH AND WE MISS IT, BUT THAT IT IS TOO LOW AND WE REACH IT"  MICHELANGELO
6/1 METRO, 6/1 LISTER SOM, 6/1 LISTER, 1 1/2 HP LISTER D, LISTER PUMP,LISTER PETTER LPWS4

GuyFawkes

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Re: Crank Straightness Tolerance
« Reply #5 on: August 19, 2006, 04:54:30 PM »
Quote from: rjcroc on August 19, 2006, 04:26:32 PM

Guy, thanks for the info. Where did you measure the .0005? Even with the crank on rollers at the bearing mounting location I only measured .002 but I also checked at the ends of the shaft and also got .002 so I thought the crank was relativly straight. Now I still get .002 near the bearing mount and .010 at the end. Did you mechanically straighten or use spot heat to straighten? Thanks again. Im going to make this basterd into a silk purse if it kills me.

Rick

lathe chuck and live centre plus dial gauge, measured along the full length.

straightening was done with a fly press with the weights removed, cautiously. lead sheet between press and shaft to protect shaft.

setting up in the chuck and live centre took ages each time (from memery) as did heat treatment, the straightening and measuring (+ marking (french chalk)) was very quick
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Original Lister D, megasquirt multifuel project, compressor and truck alternator.
Current status - project / standby, Fuel, good old pump diesel.

cujet

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Re: Crank Straightness Tolerance
« Reply #6 on: August 19, 2006, 06:12:45 PM »
While two thousandths is a lot for a normal engine, I suspect in the listeroid world it is near OK. Ten thou is really too much. It should not be too difficult to get it right.

Chris
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