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A friend called me up yesterday after a mis-adventure during his attempt at a bottom bracket overhaul. He stripped out the threads on the (left) crank arm while using a Park crank puller. In a pinch, we rented an automotive gear puller but could not get enough purchase for that to work.

Any tips on this? Especially a way that will not ruin the crank arm. (I know, the crank arm is now ruined in terms of future removal, but in the meantime with a bottom bracket overhaul and without any further damage, it'll get him through another season's commute.)

Update 12/31/2011 This question was asked over a year ago now, so problem solved at that time. Followed the advice by whatsisname and we got the crank arm to loosen by slowly riding around the block a few times. Once it was loose, we were able to finish the job using some strategic tapping with a padded dead blow hammer. Then replaced/rebuilt the entire crankset and bottom bracket. (The thing was trashed beyond the removal issues...) The recent additional answers may be of use to others who find themselves in a similar predicament.

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This last time I did this, it was because I hadn't remove the crank bolt. Oops! Once I got it off, the remover screwed in all the way and the crank came off easily. –  Jay Bazuzi Nov 23 '10 at 0:22

7 Answers 7

up vote 9 down vote accepted

Your crank arm is trashed.

With the crank bolt removed, gently ride around a few miles, it should work itself loose enough that you can yank it off.

Otherwise many shops have basically a slightly larger crank puller for addressing this issue, where they chase out a larger set of threads, then use the larger puller to get it off. The crank arm typically goes into the garbage at that point however.

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This is actually what I told my friend. I wanted to make sure that there was not a technique or "magic tool" that I was not aware of. The automotive gear puller would have worked had it been bicycle sized; unfortunately adequate leverage wasn't possible. Anyway, my friend will be getting a replacement crank. –  user313 Nov 23 '10 at 19:07

A similar idea to whatsisname's: Use a rubber mallet to tap on both sides of the crank arm, alternating between the inside & outside, so as to work the arm loose. The hits do not have to be brutal, but with enough force to get some movement happening so that the arm is loosened. Put more force on inside face, since you are trying to take the arm off, and only a light tap on the outside face. This method has the advantage of not having to get on the bike and risk an accident should the arm come off unexpectedly.

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I whole-heartedly agree that getting on the bike and riding around town with no crank-bolt is not a good idea as a method of removing this crank arm. The arm coming off in traffic could be catastrophic for the rider and possibly for other road-users. Tap it off--it's already trash--and do the replace in a controlled environment! –  DC_CARR Nov 23 '10 at 21:04
Perhaps, but if you simply loosen the bolt then the crank won't come all the way off, but will still work loose just a easily. –  Daniel R Hicks Jan 1 '12 at 19:26

If you know someone that works on automobiles ask if they have a tie rod remover.It looks like a heavy duty tuning fork with tapered ends.In the absence of one of these use two large screwdriver and wedge them between the crank arm and the bottom bracket,being careful not to damage the chainring.Tap the screwdrivers or the tie rod tool just hard enough to exert some pressure.If it doesn't pop off try to warm the crank arm with a heat gun or a hair dryer.The idea is to heat and expand the crank arm but not the shaft. As it warms tap the scewdrivers to see if it moves.You might want to apply some lubricant just be careful of heat and combustable fluids.Let it sit over night with the pressure applied and keep tapping the tool until it releases.You can also try to tap the arm with a ballpeen hammer while holding a second hammer 180 degrees opposite.The shock from the moving hammer distorts the crank arm hole while holding the second hammer stabilizes the shaft.This seems like it involves some complicated positioning and may be easier with two people until you get the hang of it

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I have resorted to that sort ball joint splitter. With some cranksets it might be possible to to it without damaging the chainrings (if they are removable chainrings worth keeping, take them off), but in my case it wasn't. (Incidentally, another sort of ball joint splitter makes a usable cotter press. Not many people have cottered cranks these days though.) –  armb Oct 4 '13 at 11:49
"Heavy duty tuning fork" type: amazon.co.uk/Draper-14159-Ball-Joint-Separator/dp/B0001K9Q2C Usable as "cotter press" type: toolbox.co.uk/draper-13914-19mm-capacity-14632-63529 –  armb Oct 4 '13 at 11:53

I've just been through this in a restoration I'm doing. I have a decently equipped shop so some people might have to find a friendly mechanic... The Park tool simply pulled the threads right out of the crank. I've not had that problem before so I know it's not me. I have often suspected that the Park tool is very slightly undersized, so this did not inspire my confidence.
I tried heat (MAP gas, don't use oxyacetylene, it will melt the crank), various solvents/releasing fluids, riding the bike without bolts up steep hills, tapping with hammers on the sides etc... all to no avail.
Finally before giving up and cutting the damned things off, I took it to my friendly bike shop where their profession-grade tool was able to dig into the remaining threadforms and just barefly get the drive side crank off...but not the other. From here I could disassemble the bottom bracket and used a 12 ton press to push the axle out of the right crank arm. The taper LOOKS OK, but before re-installing, I'm setting up to bore out the crank arms and push in a steel threaded insert. I'm going to try retaining the insert with just friction and Locktite Green (671) but it may need to be peened. Doing it this way shouldn't weaken the crank arm and will provide steel threads to pull against next time.... Not the answer for everybody, and it may be too costly to hire a machinest. Even with the tools and ability, it would probably be cheaper on some scale to just buy a new crankset, but then why replace when I can fix it?

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I just heated the crank arm up with a butane torch, grabbed an aluminium drift, laid by bike across my knees, and gave the boss where the inner chainring bolts on a firm blow with a hammer using the drift. Came off real easy.

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Thought: Go to a building supply place and get a bundle of tapered shims. Probably the plastic ones would be best. Insert four shims, in pairs, with opposing tapers, one pair on each side of the crank shaft. Tap the shims in tighter and tighter until the arm pops off (or the bearing cup pops off, whichever occurs first).

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I asked the question in November 2010, so this is a tad late. However, your answer may be of value to someone else in the same predicament. –  user313 Jan 1 '12 at 19:59
Or until the plastic shims crumple and break. @mikes tie rod remover is more effective. Does depend just how stuck the crank is of course. –  armb Oct 4 '13 at 11:54

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