I'm trying to remove the bottom bracket from my old mountain bike but the cup side (non-drive) is stuck.

I've got the crank arms removed and have removed the cartridge from the drive side (Drive side being reverse thread) but the non-drive side is infuriating and is not moving in any direction.

The spline drive I'm using has almost shattered the teeth on the cup itself trying to remove it. I've let is soak in WD40 for now and will go back again shortly but I'm debating cutting it out with a dremmel as a backup (but I'm not sure if that'd ruin the threads on the bike).

Can I leave the non-drive side installed and insert the new bearing and cartridge from the drive side instead?
Or any tips on how to remove it from the bike?


\\before it comes up: I understand that the non-drive side is a standard thread (as the drive side is reverse). Counterclockwise should remove it.

Metal cup, I'm assuming? Try using a crappy old flat-blade screwdriver you don't care about and a hammer, setting the blade on one of the splines and try to spin it out that way

A long M8 bolt with some washers is a good way to secure the tool against the NDS cup for removal. You'd need to put the BB back in for that, but no big deal.

Consider the circumference of the BB shell. Think about how little of that you might lose if you are somewhat skilled when you cut the ring out.
In short, don't worry about it.

If your really lucky it will be plastic (Shimano UN54), this can be cut out with a mini hacksaw, if metal, and you have a vice, stick the tool in the vice, and rotate the frame round it (you may need to secure it as #ThermionicScott suggests

I've done this many times with steel and cast iron plumbing pipes of various sizes. I used a Sawzall - definitely not a fine surgical instrument! Even when I grazed the internal threads, it didn't present any problem at all. Your Dremel wheel will offer much greater control.

It's best to make two cuts with a small space between them. Then, knock out the little piece, gently tap the ends of the big piece inward, and unscrew it.

Thanks guys.
The M8 screw idea to retain the tool is a brilliant idea to allow me to get more leverage without the socket camming out of the cup.

If that fails: cutting

Don't forget to soak threads with PB-Blaster.

You can buy screwdrivers designed to be hammered on like a chisel. They're awesome.

This is what I use.
You'll have to adapt bolt length/washer stack for your spindle length.


I'd suggest getting some REAL penetrating oil.
Lay the bike over on the NDS, level as you can, and apply through the shell to the threads so that it can run into them.
Let it soak for 20-30 minutes.
Rap the cup with a wrench or ??? to "vibrate" the oil in. Light taps, not heavy handed swings. Pretend you're ringing a bell.
Repeat a couple more times.
Remove cup.

Quick update: it was near-welded in by the factory by being very badly cross threaded. Whoever installed it HAD to have known what they did. The threads on the non-drive side are, sadly, destroyed (either from initial installation or from my removal).

Well... There goes that frame. Maybe one will pop up on goodwill

It was a cheap bike that gave me ~10 years of it's time (that being said: I think I've ridden my new road bike more miles this year that I did ever my MTB)

There's no need to give up on the frame just yet -- Velo-Orange offers a threadless cartridge BB. Not cheap, but should last long enough to be worth it.

The frame threads can probably be cleaned up. Take the frame to a bike shop, ask them to chase and face the BB - takes less than 5 minutes. If the frame is steel, the thread in the frame is a lot stronger than the treads of the BB cups.

If the frame is aluminum, VO and Sunlite (Niagara Cycle has them) make BB for installation into frames with striped BB threads. The Sunlite ones are very reasonably priced.

I used a motor tool (Dremel equivalent) with a cutoff wheel to get an old cro-mo cup out of a Trek 950. Took the frame over to Wheel Away in Campbell, they ran their Park Tool thru the BB, chased and faced. No issues.

Thanks guys. Investment cost is a significant consideration on this fix considering the quality of the vehicle to start with.
Great options I didn't know I had.

Where in Ontario are you located? If you are in my neck of the woods, I might be able to chase and face it.