Removing a crank with a destroyed thread

[Punkawallah]

Still working backwards: does anyone have an alternative to a blowtorch to remove a cheap and nasty plastic cup-and-cone bottom bracket?attempts to remove it conventionally just broke the plastic (and yes, I was turning it the right way).

I’d avoid a blow-torch. The burning plastic could give off all sorts of noxiousness (even for a bike workshop), and if it melts into the BB threads you’ve got another headache. This might give you ideas, although the BB concerned was aluminium in steel:

View: https://www.youtube.com/watch?v=SPHD9VMj43U

 

[Punkawallah]

But make sure in Space first

It’s the only way to be sure ;-)

 

[Ajax Bay]

Echo caution with caustic soda. A father of our son's fellow U10 rugby team member used this on a sink and is now blind in both eyes.
On the BB's plastic cup (left hand side), which is now broken beyond repair, I had this problem - the 20-spline tool munched the plastic - but I got it out by unscrewing the (metal) drive side cup. However this option is not available to the OP till he cuts off the crankset.

 

[rogerzilla]

Hacksaw and chisel is what I've used.

 

[Wobblers]

Some research has revealed that Würth make a drain cleaner which uses Potassium Hydroxide, which apparently has the same effect on aluminium, so I now have a source if/when all other alternatives fail (and I've got the BB our of the frame)

Potassium hydroxide, or caustic potash, is just as nasty as caustic soda (which is sodium hydroxide). In my opinion, both are easily as dangerous to eyesight as any of the inorganic acids. I'd suggest using washing soda (that's sodium carbonate) instead: it has the same chemical action on aluminium as hydroxide, but is very much less aggressive. You'll probably have to leave the solution in contact with the stuck seatpost for some hours to give it time to break down the protective oxide layer on the aluminium.

 

[Andy in Germany]

Potassium hydroxide, or caustic potash, is just as nasty as caustic soda (which is sodium hydroxide). In my opinion, both are easily as dangerous to eyesight as any of the inorganic acids. I'd suggest using washing soda (that's sodium carbonate) instead: it has the same chemical action on aluminium as hydroxide, but is very much less aggressive. You'll probably have to leave the solution in contact with the stuck seatpost for some hours to give it time to break down the protective oxide layer on the aluminium.

That is useful information, thanks. If it works it's even better than the caustic soda because we could use it with clients (I'm not letting my clients near caustic soda; they don't have the capacity to do risk assessments) How do you apply the baking soda? Pour down the baking soda and add water?

 

[fossyant]

Is this crank off yet ?

 

[Andy in Germany]

Is this crank off yet ?

Not yet: I've ordered a pull tool, and it will arrive next week at the workshop; I'm on holiday, but I'll be going in on Friday because the training currently includes wheel building theory. I'll have a go at the crank after that; then the bottom bracket.

 

[Big John]

RJ the bike Guy has become very proficient with that bearing puller and makes it look easy. I've got one of these pullers and I got nowhere but, in fairness, I hadn't watched RJ's video before I used it. I think it may work so good luck Andy.

 

[Hover Fly]

Long time ago, I adapted the inner screw in part of a commercial crank puller to fit a home made* to fit the cranks 3 arm puller, the crank came off quite as easily as with any extractor made to fit the threads. No corrosive s or heat involved. The crank, a Stronglight steel 49 and bottom bracket were still usable.
Remember the pin of the extractor must touch the axle, not the inside face of the crank, a rookie’s mistake I’ve seen made.
* Lathe and mill were involved.