Stripped Crank Arm
 

An unnamed knucklehead stripped the threads on my Alivio crank arm (square bottom bracket).

Does anyone know any good tricks for getting it off, or am I going to have to resort to a bandsaw?

TIA, Mike

I feel for you. I've lost a crank or two that way, even after stopping and using lots of penetrant after the pulling got hard. Sometimes the crank threads lose the battle - even sadder when it's a rare and valuable old crank you wanted to save.

I've tried a jaw puller, but with 0% success. What has worked is multiple cuts with an angle grinder, working carefully in case you want to salvage the bottom bracket.

https://www.harborfreight.com/16-in-...iABEgIRmvD_BwE
Of the appropriate size-

Often, removing the mounting bolt and riding around the block a few times is enough to work the arm loose. Don't go too far from home/shop, as once it gets loose you'll want to stop riding and walk back, or risk ruining the crank arm. There are kits to cut new threads into stripped arms; too costly for a one-off job, but perhaps a local shop has one.
https://cimg1.ibsrv.net/gimg/bikefor...f2b2dae446.jpg

One trick is to go ride the bike with a crank arm retaining bolt only finger tight. In time the crank will come loose and the bolt will keep it from falling off the bike while you limp home. Andy

A variation on this----

Back the bolt off half turn from tight, and do sprint intervals near home. The arm will come free with an audible pop.

If that fails, leave the bolt off and join some friends on a century in the Poconos. (based on experience)

Otherwise, buy a pair of #6 Jacob's Chuck wedges for a few dollars.

Sounds like the crank arm is already ruined, but yes, loosen the bolt and ride. If a local bike shop has a tap to recut the threads, the crank arm might be salvageable.

This is a common misconception. Unless the damaged threads are limited to the outermost few, you cannot magically cut new threads to save a stripped crank. While it might be possible to restore some thread by chasing (not cutting) the damaged threads, they simply won't have the strength needed for pulling a crank.

Likewise, tapping new threads, would mean a larger size for which you'd need to seek a non-existent remover.

HOWEVER - if one ops to use Jacob's Chuck wedges, the crank can be reused and removed the same way as often as needed. Likewise, with the ride till it comes loose approach, though that would be less convenient.

In summary, I see no need to "fix" or trash the otherwise good crank arm.

One trick I used once was to loosen the bolt a turn or two, get yourself an assistant to hold the bike a few inches off and parallel to the floor by holding onto the crankarm or chainrings and then you use a drift to give a decent smack to the head of the crank bolt. This should move the crank just enough to come loose from the BB axle. Don't get too carried away with the hammer and may take a few hits. Heat to the crank first may help a little but to be safe pour some boiling water over it rather than a flame.

Use a bearing seperator/puller if you wish to salvage the crank arm. It will do the least amount of damage, if any.

https://cimg8.ibsrv.net/gimg/bikefor...68e5316ea4.jpg

JA Stein made (makes currently?) a crank extractor thread repair kit It has an oversized thread tap (pilot too IIRC) and the now oversized extractor/puller.

Bicycle Research and BR offered an extractor thread chaser w/ pilot. here's a shot of it. Andy
https://cimg2.ibsrv.net/gimg/bikefor...6aaf710734.jpg

I've had that fail several times, on cheap MTB cranks with riveted chainrings. I couldn't get the wedges placed in way that didn't end up blocked by the inner chainring.

That's how the VAR kit I mentioned above works. It cuts new, 24mm x 1.5mm threads, and then sell the customer the 24 x 1.5 thread self-extractors for subsequent crank removals.

True, but my rule is try the easy way until/unless it won't work. The beauty of using these (which used to be dirt cheap) is that when they work, you know that are can be reused and remover the same way, saving the cost of replacing.

Yes, and BITD we also sometimes retapped cranks to use Stronglight removers. But, IMO, we need to self impose cost limits for saving anything short of a true collectible.

One time the outer few threads on a crank arm were buggered up and I just couldn't get the crank puller started. I machined a steel rod to both fit closely into the bolt hole of the bottom bracket axle (so the rod was square) and a close fit on the hole in the crank puller. Once the crank puller was all lined up I was able to get it started. Carefully working it in, I eventually got it all the way seated and had enough threads into the crank arm to allow the puller to work. This is not very helpful advice if you don't have access to a lathe, however. Sorry if this therefore doesn't help!

....I have one, and it works well. The little inserts he makes, to turn the crank arm back into one that accepts a standard puller, are only available sporadically. But he does list them on his website. All his stuff is well made and very functional. I had several classic cranks that were stripped by less skilled mechanics, over at the bike co-op here. So for me it made sense as an investment.

https://steintool.com/portfolio-item...-system/...175 bucks (ouch).

For the OP, I would just either find a pickle fork, or an angle grinder, destroy that Alivio crank removing it, and replace with something better. But I have stuff that is better.

...

...

Drill chuck wedges.

https://www.bikeforums.net/bicycle-m...dge-sizes.html

Andy, this tool looks essentially like what was trying to describe. I'm guess that the smaller threaded 'stud' screws into the axle of the bottom bracket and it aligns the thread cutting portion. I didn't know they made such a thing. Very cool!

Thanks everyone!

Riding it with the crank bolt loose sounds promising.

And the other end of the pilot threads onto "stud-type" axles. But it only works if the arm threads are damaged, but not stripped. And AFAIK, it's been out of production for many years now.
https://cimg4.ibsrv.net/gimg/bikefor...255dd7238f.jpg

Easy enough to make one, find a buddy with a lathe.

And can harden the tool after single pointing and slitting. Andy

Is it worth the effort for a few uses? Just cut the two threads in some cold rolled round bar - done; you could knurl it or mill flats for easier use. And you'd have to mount the crank on an axle (or mount it on a face plate) and thread that too. People do this stuff for fun, you just have to find them.

J.A. Stein also makes a version of it. I have one of those along with an extractor tool.
EDIT: Guess it was already mentioned, but I will say +1 to those that say it works well.

just loosen the bolt and ride around the block a couple times.

/markp