Trueing a crank

[ippielb]

I am wanting to true my crank, have it out of sled on the bench. I do not have b blocks, and don't see myself spending $300 on a set. I was wondering about what you can use instea of v blocks. I was thinking about using hardwood. Cutting them to use as v blocks.

I was also wondering what tools you use? From my understanding its only pinchin and spreading the wheels on the crank corresponding the high and low points shown by the dial indicator. Which would be a large chisel shaved down to become a wedge to spread the wheels, and then a pair of heavy hammers and a vise grip to pinch the wheels with the hammers.

Is there something I'm missing? My cranks are only 0.004" but I feel that's too much. I want to be 0.001" or less.

 

[XxXModRods]

Your on the right track bro. Good luck getting down to .001. 002 is all i could get out of mine. Mine was at .004

 

[Rixster]

Go watch the guys at a machine shop true a crank, they used a BIG brass hammer !! They literally beat it back to true. It is quite a ugly process .

 

[ippielb]

Thats exactly what i thought, but guy on hardcore sledder told me i needed "special tools" and everything. Brass still seems hard to me, i dont know if i would trust it to be honest. I just can't find a big solid lead hammer.

Anyone have idea's for V-blocks? I want to set mine up somehow in the vice. to hold it sturdy but to allow it to spin freely without hitting anything.

Very interested to see anyone else set ups. If anyone could post a picture.

 

[mike_s]

Big brass hammer, to get the throws to twist. Large bolt cutters with the jaws cut wide enough to pinch the throws. Half inch breaker bar to spread/twist the throws at the same time. Cold chisel to spread throws without twisting.

As far as a fixture, we built one out of a large vise grips clamp and welded some heavy channel iron on in place of "V" blocks. All it has to do is hold the crank stable whike you read the dial indicator, take it out when you do all the smacking and tweaking and twisting.

I remember doing this when i worked for a shop here, and people would peak through the window just as i would wind up and wack their crank. They yelled at the boss once. LOL!

 

[ippielb]

Haha, thanks for the informative post. Could you explain the breaker bar part, where you spread and twist, what would be the situation for this? I will look into finding a big brass hammer.

 

[xpspenziv]

Google.( Dayton wire wheels). There you will find a big lead hammer.

 

[diggerdown]

I just made my own lead hammer. Old frying pan, a coleman stove, and some old wheel weights. Melted them down, poured them into a piece of 1 1/4" copper pipe witha hold in the side with a heavy rod sticking out. Drove a round piece of wood on to the rod and been beating with it for 10 years.

 

[mike_s]

Haha, thanks for the informative post. Could you explain the breaker bar part, where you spread and twist, what would be the situation for this? I will look into finding a big brass hammer.

Really no reason to use a breaker bar other than if you need to move the counterwights appart and twist them at the same time. This can be done in two separate steps as well, i just used that method to save time.

Thought on using a lead hammer: might not be as effective. With a brass hammer, you will get the force as well as a nice sharp shock to get things moving, without damaging the steel of the crank. With the lead, you definately wont damage the steel, but you will get more of a thud than a nice sharp tink. That sharp tink is more what gets things to move than the weight of the hammer.

 

[ippielb]

I splurged and bought a 3lb brass hammer for $55. Where abouts do you smack the crank to get the best results?

 

[mike_s]

I splurged and bought a 3lb brass hammer for $55. Where abouts do you smack the crank to get the best results?

It depends on where it is out of alignment. If the webs are out torsionally, then you will need to hit one to get it to twist on the crank pin relative to the other web. Basically, you just have to take note where the high and low runouts are and hit the high side...if that makes sense. This will be a fun expirience for you, you will feel like a dog chasing your tail because almost no adjustment can be done without affecting another one you just made.

 

[ippielb]

I'm about ready to throw this crank in the garbage, i've spent at least 7 hours attempting to true this crank. I thought my dial indicator was out of wack. bought a new one. My crank is not a TRUE round circle on the PTO. It has its own high and low spots. I have tried on where the bearing runs as well and i cannot get a reading either. It goes from -0.002" to 0.004 then down to 0.001 and back up to 0.007" no matter how i try to do it. I'm ready to part the sled out, buy new and leave it the Fing thing stock and not touch it.

 

[joshkoltes]

or you could send the crank to a professional first for a quote, another set of eyes never hurts

 

[ippielb]

Looking at the reflection of light on the PTO end of the shaft i can see distortions in the reflection when the high/low spots change.

I will take a video of it and put it on here, show the dial indicator reading.

 

[ippielb]

This is as best as i can get to show a true circle...

And here's another with my new dial indicator.

 

[ippielb]

So I cleaned up my ball on my dial indicator, and polished the PTO end, set up my dial indicator differently, inproved the set up for resting the crank in the blocks. Seemed that there was slight rust spots on the shaft causing the bal to get dirty, and to sway the results.

I have now gotten the PTO end on the very tip down to 0.0015" movement in a full rotation. But on the bearing race closer to the web it is out 0.0035"-0.004" movement. How could one fix that?.

 

[TVC 15]

I don't work at a machine shop. But I have been around them long enough to know trueing a crank is a art. If I wanted to learn how to true cranks I would find a old crank and hammer away. But if I had something I wanted to ride in the near future I would send it to a pro. Just my 2 cents.

 

[ippielb]

What fun would that be. Now I know how to true a crank an do it half *** decent. It's all a learning process some people like to send their stuff off and get the work done for them and say they build sleds. I do it all myself. So I know every little thing on my sled. If anything happens I know what to do and how to do it.

 

[m8magicandmystery]

should you rotate the crank via the connecting rod..??..or should ya steady the rod and rotate the crank closer to the crank center with the force generally applied down to take up brg play etc..??? ...great thread here..very interesting with lots learned..

 

[m8magicandmystery]

ps...are ya going to pin and weld it or is it just going to go out again fairly quick...??