So I needed to replace my bearings on my qu-ax 36er.
Brought bearings, bearing puller and ISIS crank extractor from unicycle.com.uk
Following instructions from their website extracted the cranks no problem.
Next fitted the bearing puller and after some tight turns the bearing popped off.
Good I thought.
NO.
When I attempted to put the hub bolts back in after fitting the new bearings and cranks I noticed that the action of the bearing puller has pressed the axle screws together near the top. Obviously in hind sight if I had used say a washer on top of the axle that would have deformed instead.
I wish that had been mentioned in the instructions, but instead now I have a hub I can’t screw the bolts back into.
What you need to recut those threads with a Tap. (I damaged my axle bolt threads using the wrong crank extractor!) I ordered the correct tap and had no trouble fixing my axle threads.
Look at this thread, especially where it references what Tap to use… good luck
You’ll need to re-tap the threads of the hub. Sometimes you can do this by merely applying some force to the normal bolt to get it past the mashed threads and into the good threads; if you can do that, the bolt will more or less re-tap the upper threads for you. (If you want to be all fancy about it, you can cut slots in an axle bolt and use machine oil to make it tap better).
Failing that, you could get a tap-and-die set, or bring it to a machinist (or possibly a bike shop) who has one. Crank bolts have pretty standard threads, so it shouldn’t be difficult to re-tap them, as long as the hub is steel. If it’s aluminum, it’ll be harder to repair the damage, but it looks like steel in the picture.
Take your time doing this. If you can, use a counter sink tool to shave off the face of the damaged thread. The thread angle is 60 degrees and countersinks for flat head screws are 82 to 90 degrees which is close enough. Using an oversized drill bit as a countersink by hand is not quite as good with a standard tip angle of 118 degrees but you are more likely to have that. It’s probably a 12mm bolt so using a 20mm or larger bit (by hand) would be OK.
After you peel off what damaged thread you can, use some kind of oil, as Tom recommended, on the correct tap (I think it’s M12x1 or M15x1). S-l-o-w-l-y turn the tap STRAIGHT in to tapped hole. Some of it will be a little difficult because you are reforming and/or recutting threads. Just DON’T force it. It shouldn’t take that much force and after 1/2 to 1 full turn it should get easy. If it doesn’t, stop and rethink it. A bolt, as Tom also suggested, might work OK but it had better be hard. The axle is probably CrMo so it’s already pretty hard stuff.
I was always taught that when tapping, you put half a turn on and then take quarter off, repeating until done. Always nice and slowly and with lots of oil.
That first part might be entirely wrong, but the few taps I’ve done have always ended well.
Excellent point. I’ve tapped so many holes (don’t even think about going there) that I forget that some people haven’t done it at all and don’t know the details. Clearing the cuttings away like this is an important part of the process.
Had the same problem recently with the same tool, my hub was a Nimbus Cromo. I filed off some of the damaged threads then managed to force the bolt back in much like Tholub describes. It worked for me thankfully and i’ve changed cranks a few time since with little problems, although the bolts aren’t as smooth going in as they used to be.
For next time, the washer in the middle protecting the threads sounds a good idea. Though I wonder how well the tool will stay in position, I had to apply a huge amount of force to get these bearings off.
I’m trying to find out what size crank bolts the Qu-ax ISIS hub uses. The ISIS spec says M12 or M15 as Harper pointed out.
Looking at the Unicycle.com.uk website the ISIS hub bolts state that they fit KH but not Qu-ax so I was thinking i would need a M12 tap but this seems to suggest it could be M15?
I pulled a bearing recently and need to replace it (I’ll try using a dime next time too). Is there a tool to help replacing bearings? If not how do you hit it with a hammer without damaging the bearing?
I don’t know what size you would need, but the first thing that comes to mind is a deep socket from a socket wrench set. You would want it to be as close a fit as possible to the axle diameter to minimize the chance of it going crooked, and you want to only put pressure on the inner race of the cartridge bearing.
To install a bearing tap it on by the inner race, using a pipe or socket. Because pulling a bearing off is done by gripping the outer race, the bearing is usually damaged, unless it was a really loose fit. So the correct practice is just don’t remove the bearing unless you have a new one to install. Just throw away removed bearings, they are supposed to be damaged by the extraction process.
Sorry I’m too late, I had replies from Qu-Ax on Thursday, but no forums access… In addition to conforming that it is an M8 thread, I had the following from Michael Erdhuetter:
The easiest way to protect the axle thread when changing the bearings is to put the hexagon screw back into the axle after loosing the cranks.
In the QU-AX toolbox is a better tool to remove the bearings, it doesnt damage the bearings when turning them off and you can use them again. Sorry for my bad English, I dont use it often.
