How do i fix threads on a 1 piece crank???

[flatblack50]

I have this old crank for my Hartford and some of the threads are messed up at where the bolt that holds on the sproket on, starts to thread on. I tryed a wire brush but that didn't help at all. I'm going to take it down to the bike shop tomorrow and see what they say. I REALLY dont want to have go with a modern crank (the bike is from somewhere between 1916 - 1933). Any ideas? Is there a special tool for the treads on a crank...?

 

[Wildcat]

I once used a magnifying glass to look at the threads and used a small file to file down a bad spot and it worked, but it was hard to get it started and I was probably lucky. Usually the threads were hit with something, like axle threads getting damaged, but those threads on the inside of the crank shouldn't have been subject to any real damage, so maybe the bike shop can get it to work. Maybe the threads on the nut are damaged, if so that would be an easy replacement.

 

[flatblack50]

The threads on the nut are fine (i still have to replace it though, it's worn really bad where the bearings ride on the other side). The treads on the crank are smooshed togeather on the first few rings.

 

[bairdco]

you can buy "thread files," which are really skinny files (also called "needle files) and file the dings out of the threads. it's pretty simple.

harbor freight has them for cheap: http://search.harborfreight.com/cpisear ... &Submit=Go

 

[Graylock]

I once bought a set of cranks for my Huffy at a swap meet. I brought the old one to make sure I got the right one. Out of a pile of them I found what I wanted but when I got home I had the same trouble as you did but on close inspection I found the threads were not the same as the old crank. I could what I thought was starting the nut but that only buggered up the threads. So I say to you hows your nuts :shock:.... are they the same thread size?
Just thought I'd run that by you, hope it may help.

GL

 

[Wildcat]

If it won't work with those threads at all, there is another way to use those cranks. I've had a couple bikes where the crank on the sprocket side wasn't threaded. The bearing race wasn't threaded either, it just slid on and the adjuster on the left side held it all together when it was assembled in the frame. You could file down all the threads and slide the original nut over and do it that way. That would be a lot of work filing it down, but you would have your original parts.

 

[flatblack50]

The bolt was on there when i got it. It came off fine, but i'm thinking maybe i got it cross threaded and messed up the threads... I have some of those tiny files ... somewhere... i'm going to have to tear through some boxes and look for them. Thanks!!!

 

[B607]

If it were mine, I'd get a Dremel and a pack of #420 cutoff wheels. Put 2 wheels on the arbor and grind off just the bad threads. Hold the wheel 90° to the threads and grind with the wheel turning away from the threads. There are more than enough threads on the crank to hold the nut/chainring after you grind off the bad ones. After you grind, hit it with a wire wheel to remove any burrs. You may or may not have to dress the lead thread with a file and magnifying glass. Gary

 

[flatblack50]

Thanks everyone!!! Ya the bolt was on there, but once i got it off i couldn't get it back on. But with a couple files and alot of swearing i managed to fix it