Stripped crank threads - Help!

[Caph]

I've managed to strip the crank extraction threads on the non-drive side crank. I'd unwittingly managed to damage the crank extractor by cross threading and then it in turn damaged the threads. The nett effect is that I have a smooth surface where once I had threads!

I can remove the drive side crank and completely unscrew the bottom bracket but that's as far as I can get.

I've tried pouring hot water on the crank then punching out the BB. That didn't work. I've tried a 3" gear remover but there just isn't enough clearance and in any case the crank has a curved profile which means there isn't anything to grip on. I've also tried drenching it in WD40 and chain oil.

Has anyone got any other ideas? Has anyone any experience cutting through the square tapered section of a Shimano BB? Will a Dremel do (I'll buy one if it will do the job) or will I have to resort to an angle grinder?

I'm ready to consider any option at the moment.

 

[Mussels]

If I'm imagining it right you need to get the remaining crank off the BB, if so then a Dremel should do it easily as the crank is a fairly soft alloy. You won't need to cut all the way through, go about 3/4 through and a swift blow to a cold chisel in the slot should split the crank without leaving a mark on the splindle.

 

[Caph]

Unfortunately for me I have the Shimano Acera M361 crankset which is one of the tougher cranks around. Think big, hard and heavy. However I hadn't thought of cutting the crank. It's a lot more accessible than the spindle anyway.

Thanks for the idea.

 

[Deleted member 4366]

When you tried punching the spindle, did you use a big hammer and drift. .A medium hammer probably has less mass than the BB assembly. Perhaps, if you try a 2lb or lump hammer, it'll shift, but be careful not to damage the BB threads. Momentum is everything under these circumstances!

 

[Orraman]

If there are any threads left you could try this link.

Park Tool Co. » ParkTool Blog » Removal of Cranks with Damaged Threads (square type only)

If you decide to saw and then chisel, it is best to rest the crank on the most massive lump of steel you can find, and use d8veh's lump hammer to drive the chisel.

An alternative might be to lay the crank on said steel with the corners of the square vertical and strike the top of the crank above the square with the hammer. Pounding vertically down on a metal tends to spread the metal sideways.
Or a 60 degree knife tool in the hardy hole of an anvil underneath and a large chisel on top ~~ know any smiths?

Dave

 

[Mussels]

If the crank comes loose and causes damage then it should be the crank that is damaged, that's why the crank should be made of softer metal than the spindle.
If that makes sense.

 

[Caph]

That does make sense Mussels.

Unfortunately the threads are completely removed. I don,t think the tool will be much use.

The point about the hammer is right though. I remember thinking that it didn,t feel like I was making much of an impact with my medium hammer. I'll try a bigger hammer!

Thanks for the help so far.