Crank extractor not screwing in properly

Question

I'm trying to insert my crank extractor into the crank of a square taper (Shimano Tourney). It won't really screw in properly. On several attempts it will go in a little bit (about 1 or 2 mm) and quite abruptly won't turn anymore, as if it didn't go in properly. It doesn't feel right. I've tried it enough times that I'm fairly sure it's not the angle I'm using causing the problem.

I am starting with the inner part of the extractor fully inside the outer part, so it isn't that the inner part is simply already pushing into the spindle or anything.

The crank extractor is the Birzman universal crank extractor.

What am I doing wrong here?

It's at this point that the extractor will 'stick', only going in a very small amount. Shouldn't it go further?

Answer 1

If you want to save the cranks, consider taking this to a shop.

Wonder if this bike was run without a plastic cover over the hole?

I suspect the threads in the crank are slightly damaged. You might be lucky and force the extractor in correctly, or you might screw-up the threads completely if it on the wrong angle

An LBS will have taps that will chase the threads back to smoothness. Taps like this are quite expensive and generally unnecessary for the home mechanic. I don't own any this size.

You can try another crank-extractor - I own two and they have subtly different tolerances. Not sure how that works but one goes in where the other doesn't, and its not always the same one that works.

If the cranks are trash already, then slap a lot of lube in and have your best effort at lining up the extractor. Your last resort is to carefully cut the crank off by grinding through the eye, without going into the BB.

If the BB needs replacing AND its the left side, you might be able to grind through the BB axle between crank arm and BB, and then use a drift to push the stubby bit out of the crankarm eye. This should save the crank arm but it will still have damaged threads. If its the right-side then the spider and chainrings will be in the way.

Answer 2

You don't indicate whether you're installing the extractor into the crank with a wrench or your fingers. It's very common for them not to go in readily with fingertips alone, and if you find that putting a wrench on it lets you get it in there then you don't have to do anything further.

Look very carefully at the threads of the crank. Are there signs of stripping or cross-threading? If there is some damage, is it to just a few threads causing a high-friction spot, or is it all or many of the threads past a certain point?

I don't totally understand why this is, but the common way in a shop to touch up an M22x1 extractor thread (as opposed to replacing a destroyed one with a larger size) is not with a conventional tap, but with a much simpler and cheaper piloted chasing tool that looks like this: They do a good job but you might notice it's pretty much the same thing as the outer part of a crank extractor plus some flutes to clear material and a reference guide, and the nature of various square taper cranks is that there's no guarantee that the extraction threads were precisely aligned enough in the first place that you'll ever be able to necessarily use the guide. (I've at least used them in situations where the guide was a no-go but it was fine in the end.)

Where I'm going here is that while there are no guarantees you won't destroy you cranks this way, if the damage is moderate or better then it's pretty reasonable to use your extractor outer bit as an impromptu thread chaser. What I would do is use a 90 degree scriber you don't have reservations about bearing down on to get into the threads and try to "clear a path" for it, doing some preliminary shoving around of errant or damaged material. Then use either cutting fluid or heavy oil to lube up the threads, guide in the tool as much as you can by hand, and then put a wrench on it and very gradually advance it. The leverage of the wrench will let you feel what's happening, i.e. whether it's totally stuck or able to make some progress. If you have some luck and it advances, do a little bit and then go back out all the way so you can clear any material, then go back in, repeating until you can work it back and fourth with no friction.

Answer 3

I've got the cranks out - I used the Park Tool CWP-7 instead of the Birzman.

It still wasn't as smooth as I hoped it would be -as others have commented - but much better. Scraped a little of the black paint off of the tool but I'm assuming this is normal. Not entirely sure what is so different between the two extractors just by looking at them, I guess the moral is to make sure your tools are fit for the job before forcing anything. Thanks all for input.