Crank truing question.

biknut

biknut

Well-Known Member
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.
 
Yep, put it in a vise though. That's how we used to do Harleys....and they probably still do it that way.
 
Bikeguy Joe said:
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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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.
 
biknut said:
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.
Click to expand...

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.
 
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.
 
tooljunkie said:
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.
Click to expand...

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.
 
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.
 
tooljunkie said:
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.
Click to expand...

I'm hip mac daddy.
 
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.
 
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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