I have a stuck UN51 square taper bb in an alloy frame. Have tried the usual gt85 etc to no avail. Struggling to keep the slotted insertion tool in place to apply any decent force.

Any suggestions gladly accepted. It’s getting me cross!

Bolt a plate over the tool to keep it in place.

Can you put the tool in a bench vice and turn the frame? Oh, and check you’re turning the right direction.. 😉

Have tried the usual gt85 etc

<Condescending question> by etc do you mean something like plusgas which may work or more gt85 type stuff that probably won’t?

Use a big washer and a crank bolt to hold the tool in place on the axle if you’re struggling to get purchase. You can then put a ring spanner on it and stand on it if you have to.

I had this problem recently. I was able to get the non-drive side cup off, but the other side was stuck. I used plusgas penetrating oil and left it to soak overnight (GT85 doesn’t work for this). I then used a g-clamp to keep the bb tool in place and prevent slipping (you may be able to use a crank bolt for this as suggested above). I also use a longer metal tube over the end of my spanner to provide some extra leverage (hitting this with a hammer may also help to get things going.). If you can’t get the non-drive side cup off then you could drill through this carefully so that you can apply some plusgas to the inside of the bb shell.

The bench vice advice wins every time for me
As you are moving the frame the lever you have is on par with a really serious breaker bar.
and keeping the frame horizontal is easy stopping the tool from hopping out.

N

Yeah tool in vice and use the frame as a lever is the best, but if you can’t do that get a (brave/stupid) mate to hold the tool in place while you turn it with a bigger bar slotted over your spanner handle, handle bars work for this if you have nothing else.

Gently warming the BB with a hair dryer can also help a bit as well 🙂

Oh, and check you’re turning the right direction..

+1 this and that it’s different each side.

Having screwed it up myself long ago, despite already knowing the thread directions are different each side and done them fine before, I just carelessly forgot one time. Much swearing later and BB is firmly stuck on.

I now double check every time. Likewise with pedals.

You might be lucky and find the other end cap is plastic which might help somehow?

Pour some plus gas down the night before.
Bolt the tool on with usual crank bolt and a couple of washers.
Put correct size spanner on the tool, ideally ring spanner before you bolt on.
Get a scaffold pole or similar.
Use the leverage.

UN51 = metal cups n’est pas?

We used to smash-out UN31s with plastic cups – rest the BB shell over a big piece of pipe and wallop the end of the spindle with a club hammer.

If you can’t get anywhere with existing tools, see if you can find a bike shop with a Cyclus BB tool – it has a retainer that screws into the spindle and means it can’t cam-out. Clamp the tool in a bench vice and use frame as lever.

Bench vice for me is WWCD!

Un51 wow guessing that’s been in the frame a while.

Some heat , bolt the tool into the cup just remember if it’s the left cup you will need to undo the bolt as the tool starts to turn.

Big bar and socket over the BB tool.
I don’t like hurting my shoulder so use a very long 3/4 drive breaker bar

I’d take it to a shop. They’ll love you for it 😉