Crank Removal Problems

[GideonReade]

I had the same problem a week or two ago, posted viewtopic.php?f=5&t=137259&start=45

Didn't succumb to puller + heat.

Finally put a sacrificial longer bolt in the end of the BB axle, rested bolt head vertically on a brick (bike etc attached, lying down), and hit the inside of the crank arm with a slightly padded hammer. I used a hot air gun as well, and I had to hit it hard, and a fair sized hammer. I was concerned to keep bike frame and crank, happy to risk BB/Axle, it was those I wanted to replace.

[SimonCelsa]

I then take the bike outside and empty a kettle of boiling water over the crank. This usually expands the crank enough to get it off the taper fairly easily.

I can't quite fathom this. If the crank expands then surely it will get tighter on the taper? i.e the square 'hole' in the crank would get smaller as the crank material expands, thus making it tighter!

You want to freeze the crank with a good blast from a CO2 extinguisher (or similar).

Comments as to the validity of the above welcome!

[GideonReade]

I'm tempted to say you need a mathematician to prove that. But, consider the simplified case of four equal lengths of ally, joined at right angles.

Let's assume each piece is 100mm long and 10mm wide.

If they get hot the ally expands. Let's say 1%. So they will be 101mm long and 10.1mm wide. Let's assume growth is from their centrelines in each dimension.

So, across the inside faces, the dimension will be increased by the increase in the side length (1mm), and decreased by half of the increase in two side widths (0.05mm * 2 = 0.1mm). So the inside faces will be 0.9mm further apart.

(I ignored the thickness of the corner joints to simplify arithmetic).

Thus, holes get bigger when enclosing body is heated.

I hope that's right, it's decades since I studied mechanics...

[Marcus Aurelius]

Spray a bit of penetrating oil into the hole, and tap the crank off with a dead blow mallet.

[Pebble]

I then take the bike outside and empty a kettle of boiling water over the crank. This usually expands the crank enough to get it off the taper fairly easily.

I can't quite fathom this. If the crank expands then surely it will get tighter on the taper? i.e the square 'hole' in the crank would get smaller as the crank material expands, thus making it tighter!

You want to freeze the crank with a good blast from a CO2 extinguisher (or similar).

Comments as to the validity of the above welcome!

Heat definitely works - spent many years working on older wagons, but you do need a lot of heat, general rule was heat the nut up to cherry red with the oxy-cetylene torch. I doubt a bit of warmth from a hot air gun or kettle would help.

But saying that, cranks are alloy and that will expand a good deal more than steel.....

[drossall]

I can't quite fathom this. If the crank expands then surely it will get tighter on the taper?

I've always understood that the key thing is that the two metals expand at different rates, which breaks the join between them. You're not really trying to get one to expand off the other, just to get the two surfaces to move against each other, even fractionally.

[SimonCelsa]

That sounds plausible!!

[David9694]

Two frames arrived this week both with cranks still in - photos show components still attached - why? I must be going soft - I’ve not experienced stuck cranks before.

I had to attack one l/h alu square taper with the Dremel - the threads were completely borked. I cut the lock ring off to get it out of the way. The b/b shell needed a pin spanner - getting that to move would also have solved the problem.

Anyway, I cut in either side at 90 degrees to the arm and eventually a forceful lateral bend made it come away. No amount of hammering or jiggling in the vice had done anything.

I did wonder if anyone had ever tried recutting the crank threads?

I didn’t know the tapered puller existed (upthread) but I think in this instance it was beyond any redemption.

The next candidate is a very nice Ultegra octalink. I think they’re meant to be self-extracting - but no. I’ve not come across this system before so advice welcome. The M15 bolt wears a threaded collar. On one side, the collar I found to be on the wonk - there seemed no option but to remove both, which on the wonky side needed a fair bit of torque.

But with the hollow axle, the crank puller has nothing to bite on. The next step seems to be a Shimano part that sits on the end of and widens the nose of a standard crank puller - I assume that’s the difference as regards the dedicated ISIS pullers.

[gregoryoftours]

I did wonder if anyone had ever tried recutting the crank threads?

I didn’t know the tapered puller existed (upthread) but I think in this instance it was beyond any redemption.

The next candidate is a very nice Ultegra octalink. I think they’re meant to be self-extracting - but no. I’ve not come across this system before so advice welcome. The M15 bolt wears a threaded collar. On one side, the collar I found to be on the wonk - there seemed no option but to remove both, which on the wonky side needed a fair bit of torque.

But with the hollow axle, the crank puller has nothing to bite on. The next step seems to be a Shimano part that sits on the end of and widens the nose of a standard crank puller - I assume that’s the difference as regards the dedicated ISIS pullers.

Var and Cyclus sell a crank puller set that actually cuts bigger much coarser threads in damaged cranks. Works very well but costs A LOT and the same puller has to be used in the future with the crank, although some self extracting bolts are provided with the same new puller thread pitch..

It sounds maybe as if your octalink bolts are self extractors but the collars were installed badly or weren't up to the job. Most normal octalink bolts are indistinguishable from regular square taper bolts from the outside.
To remove an octalink crank without the correct puller you can just use a thick washer of the right size for a normal square taper puller to bear against, laying the bike on its side and obviously taking care that the washer doesn't move out of place as you nip the puller up.

[andrew_s]

As it is there is no great emergency to get it off. I was only removing the cranks to repaint that part of the frame, and I can do that with the left hand crank still attached. There could be many thousands of miles left in the currant BB.
Would still like a plan and everything in place for when it does need to come off.

In which case, just paint the frame with the crank in place.
When you've a replacement LH crank available & ready, put it in your saddlebag, take the crank bolt out & put that in the saddlebag, along with a suitable spanner/allen key, and carry on riding.
In due course the dodgy crank will come loose, and you can then put the replacement on in its place.

It may be 10 miles, or you may be riding 2 or 3 weeks, but it will come off in the end. The last time I saw this method used, it was a couple of weeks, the crank coming off in Heddington, half way between Calne & Devizes (home being Cheltenham)

[andrew_s]

I can't quite fathom this. If the crank expands then surely it will get tighter on the taper? i.e the square 'hole' in the crank would get smaller as the crank material expands, thus making it tighter!

No, the crank remains exactly the same shape as it expands (given even heating), which means that the hole gets bigger in the same proportion as the crank itself.

The lengths of the sides of taper increase, as well at the width of the metal between the taper hole and the outside edge of the crank.

[rjb]

You need a home made puller like this knocked up from a chainring.

[David9694]

R/h chainwheel is off - now I’ve figured out the way the self-extract bolts work.

L/h, the threads aren’t great; Shimano bolt collar (deliberately a bit flimsy?) doesn’t grip. Extractor seems to go in ok, but when I put in a washer (from a crank bolt) the end of the extractor pushed through the hole.

[David9694]

You need a home made puller like this knocked up from a chainring.

I like it - engrave it with Campagnolo and sell it as a bottle opener for £149.99!

[GideonReade]

You need a home made puller like this knocked up from a chainring.

It's gorgeous. But I doubt it would work in hard cases: My much more industrial one (that I too made by hand in 1986 or so, at RR Tech College), ultimately just stalled, I couldn't get any more force on. Plus not all crank back faces are conveniently square with room around, that's not going to fit in. I had to fashion an adapter. And add heat. Still stalled. A more brutal method with a big hammer ultimately succeeded.

There must be a task it could do to justify such an elegant existence though...