I think I would try to do it with a two-armed bearing and wheel puller rather than trying to rethread the crank while it’s attached to the axle and hub. Also, I don’t know what that thread dimension is. If you can get it off with the bearing puller by grabbing it from behind then you can throw the crank in the trash where it probably belongs or get it rethreaded then.
Here are some images of wheel and bearing pullers available in most autoparts stores for not too much money. Maybe you can borrow one from a shop or a friend. I think the one in the upper left hand corner is a two arm. A three arm might work but I think the long part of the crank might get in the way.
After you manage to get the crank removed it should be possible to get those threads retapped to clean them up. A good bike shop should have a tap of the right size. It’s not unusual to strip those threads so a good bike shop should already have the tools.
If the threads are really chewed up it might be necessary to use a helicoil. I’m pretty sure there are standard helicoils for that thread size. But if you have to go through the trouble of putting a helicoil in then it might be easier to just get a new crank if it’s not an expensive crank. And again, a good bike shop should have the right helicoil and be able to install it.
Oh oh, I got the tool (thanks guys) now here’s problem #2
The bottom of the crank - that the 'armm’s of the tool fit onto are rounded. there is little room between the bearing and the crank. the tool ceeps slipping. resting the ‘legs’ on the other side of the bearing would fit, but this will pull the bearing and crank off together (in theory)
My limited experience doesn’t allow me to decide on my own if this would be hazerdous to the bearing.
Is it a good idea to just try and ‘cut’ the crank arm off? Maybe a grinding disc, or juigsaw? I’m thinking a cut down to the spindle to the top spindle flat, the the right. This would take off the whole corner , and, in theory, have the crank fall off.
the bearing is bigger than the crank. A hacksaw or jigsaw can’t fit in to make a easy cut. Maybe diagonal cutting?
If you can’t use pedal motion to loosen the crank you could try alternately tapping each side of the crank end with a rubber mallet to mimic pedal pressure. Make sure it’s made of rubber, plastic or leather and not metal - I know you no longer care about marking the crank but a metal hammer could stress the axle and cause it to break later. Don’t wallop it hard assuming one blow will fix it, just use medium weight and lots of taps to slowly work it loose. Be patient and the taper of the pyramid axle will work the axle off.
If the mallet doesn’t work then you will probably have to pull the crank by pulling the bearing as well. You might get lucky and not damage the bearing. But even if you do, a bearing is not that hard to replace - much easier and cheaper than a new axle.
Of course if its a profile splined axle you could bang away at it all day and it’ll never come loose this way - only the bearing puller will work.
Bad idea to use any kind of saw. Too easy to misjudge or slip. Put a notch anywhere on the axle and you’ll set up a weak point where the axle will eventually break.
What about one of those tool marking etchers? You know, the ones that vibrate and make a hellacious noise and then scratch your name onto hardened metal tools. I wonder if that would work the crank loose. I think maybe all of the energy would be dissipated at the surface because the frequency is so high. Maybe an orbital sander with just the pad. That’s a longer stroke and lower frequency and larger surface area.
OK, Sofa. Get something wedged in between the bearing and the crank to pre-stress the crank. A wooden wedge maybe. Then press an orbital sander pad up against the crank and vibrate the hell out of it.
You may be able to clean up the threads with a
“thread restoring” or “thread repair” file, followed
by a tap.
Machining->Taps and Dies
Machining->Thread Restoring Tools
You’ll probably want a “hand tap”, one without
the pointy end on it. You need to measure the
hole diameter with inside calipers, and the
thread pitch with a thread pitch gauge in order
to select the correct tap/file size. Most of this
stuff should be available at auto parts stores.
It may be less hassle to take the Uni to an
automotive machine shop and have them
do the job. I’d expect they could do it
for $20-$30, about the cost of the tools
Sometimes auto repair shops think unicycles are cool and will help for free.
I still like the idea of vibrating it off. If you have someone to help you and you don’t like the wooden wedge idea to pre-stress the crank, try this as a vibrating aid. Have your assistant place the blade of a large (largest possible) screwdriver against the INNER race of the bearing. There should be a stop on the axle so the bearing won’t go in towards the hub. Pry between the INNER race and the crank while you vibrate it. I think it will work loose like that in a jiffy (where a jiffy is an undefined but reasonably short period of time).
I did grind off a crank once. It took forever and I had the use of a good 4
1/2 inch angle grinder. I did it with a sanding disc because that is what I
had handy. I was careful to only grind just far enough to not quite hit the
spindle. I found I did not have to quite grind through the crank as the
grinder made so much heat that the crank worked loose before I was actually
grinding on the spindle. I do not recommend this method except as a last
resort. I do not know what the heat of the grinding might do to your bearings,
although bearings can be replaced. My bearings were not harmed. It was a
A propane torch might be better. Try some Liquid Wrench or other penetrating