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Norm's 2 stroke repair center Having problems with your 2 stroke motorized bicycle engine? Just ask Norm, he loves to tinker and troubleshoot engines


Crank truing question.

Having problems with your 2 stroke motorized bicycle engine? Just ask Norm, he loves to tinker and troubleshoot engines


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  #1  
Old 03-27-2012, 11:13 AM
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Default Crank truing question.

A friend of mine told me he's seen people take a hammer and strike the flywheels on little pressed together crankshafts like our china girls have, to true them.

Has anybody ever heard of anyone doing this? I'm sure he's talking about having the crank in your hand, not in the motor.
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Old 03-27-2012, 04:17 PM
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Default Re: Crank truing question.

Yep, put it in a vise though. That's how we used to do Harleys....and they probably still do it that way.
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Old 03-27-2012, 04:38 PM
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Default Re: Crank truing question.

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Originally Posted by Bikeguy Joe View Post
Yep, put it in a vise though. That's how we used to do Harleys....and they probably still do it that way.
Thanks for the reply.

Well, I've got a couple of new cranks that aren't very true. I guess I'll give it a try.

I assume we're talking about twisting one of the flywheels on the crank pin. Sounds easy enough.
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Old 03-27-2012, 07:39 PM
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Default Re: Crank truing question.

Quote:
Originally Posted by biknut View Post
A friend of mine told me he's seen people take a hammer and strike the flywheels on little pressed together crankshafts like our china girls have, to true them.

Has anybody ever heard of anyone doing this? I'm sure he's talking about having the crank in your hand, not in the motor.
Well, you have to have the crank chucked in a lathe. Then it is solidly and accuratly mounted. Then you use a dial indicator on the other crankshaft wheel to tell when it's true.
I've seen this done on dirtbike cranks after pressing apart to change rod bearings.
They are normaly barely pressed together, trued on the lathe, and then pressed all the way, and re-checked in the lathe. I doubt that you could control the amount of movement, of if it would move at all, completly pressed together.
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Old 04-07-2012, 03:47 PM
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Default Re: Crank truing question.

as Wayne Z said,setting it up in a lathe and dialing it in with a dial guage and a hammer it the typical method,vee blocks are also used.
generally a couple small tack welds to prevent it from moving out of alignment.
in some small engine manuals it is outlined very well-the area to strike to give correct alignment.
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Old 04-07-2012, 09:33 PM
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Default Re: Crank truing question.

Quote:
Originally Posted by tooljunkie View Post
as Wayne Z said,setting it up in a lathe and dialing it in with a dial guage and a hammer it the typical method,vee blocks are also used.
generally a couple small tack welds to prevent it from moving out of alignment.
in some small engine manuals it is outlined very well-the area to strike to give correct alignment.
So it sounds like it's common practice to strike the flywheels for truing?

I'm going to buy a 20 press from harbor slave, and start trying.
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Old 04-08-2012, 07:20 AM
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Default Re: Crank truing question.

you will also need a dial indicator and a magnetic base and a set of vee blocks.the press is for dismantling and assembling the crank.i wouldnt attempt to align it with the press,the risk of bending the shaft is quite high.
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Old 04-08-2012, 08:19 AM
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Default Re: Crank truing question.

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you will also need a dial indicator and a magnetic base and a set of vee blocks.the press is for dismantling and assembling the crank.i wouldnt attempt to align it with the press,the risk of bending the shaft is quite high.
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Old 04-08-2012, 03:46 PM
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Default Re: Crank truing question.

now all i need is to find the manual for aligning crank and post the generic info up on here.i think its in a polaris snowmobile manual.
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Old 04-10-2012, 01:11 PM
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Default Re: Crank truing question.

I have watched a mechanic "rap a crank" into true after it pressed together. It was properly suported & braced to nudge the alignment...It was a yamaha service shop at that time....He sold the yamaha name to the local super dealer & he's importing chineese bikes now.....

so you can true a crank with a hammer.....but its not just going crazy with a 2# maul. you need the proper measuring tools & fixtures.

This shop ruled the flat track engine builds when the DT360 engines were the ones to beat on the short tracks in the midwest.
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