Stupid plastic crank dust caps...
 

I was going to remove a crank from an old bike, and so I used the nice wide blade on my crank puller to remove the plastic dust caps... I kept applying more and more pressure until the blade twisted destroying the cap. I then tried the other side with the same results.

Now, I am busy trying to remove the remnants of the caps, and realized that if I get too aggressive, I could destroy the threads in the crank.

Now through my efforts, most of the caps are gone except for the threads...

Has anyone successfully removed the remnants of plastic dust caps from a set of cranks without destroying the threads?

Any help would be appreciated!

Is it the harder plastic that shatters without bending or the kind that will bend and deform a little?

If it is the hard plastic type I'd try and shatter it by prying inward with a small screwdriver or striking the screwdriver from behind to push the plasitic away from the threads. Do this until a portion of the inner threaded ring was opened and then it could be squeezed and pulled out or further shattered until all the threads were just small curved bits that would not stay pushed out against the crank threads.

If it is the bendy-soft type of plastic then I would take an exacto-blade and score the inside of the ring that is left and then try and peel it out -bending the ring into itself as soon as the scored part broke and the "C" that was left could be pulled inside of itself. Or just carefully insert a small flat screwdriver in between the plastic and the alloy threads and try and peel it inwards and away from the threads enough to cut or grab to yank out.

Plastic is not as hard as aluminum so if you just yank/pull/hit at the plastic it can't hurt the aluminum. The plastic "threads" should fail and strip WAY before the alloy ones will. Just be careful with any metal tool up against the alloy threads.

One other option is if you can get a narrow shouldered crank-nut socket in there past the plastic bits you might be able to remove the crank bolt and then use a regular "3-arm" automotive gear-puller to pull the arm off without removing the plastic first which might just pull the plastic out or at least allow you to work on the crank up on the vise.

Man - I hate it when this happens - I don't think it can be avoided although a geaser told me to heat up the outside of the crank slowly before trying to back out the cap - Once they have more or less shattered I just use my little trusty butane torch to spot heat the remnants inside the threads then just pick them out with a small screw driver - Of course you have to be careful of heat sensitive finishes and other parts but on a vintage bike this might not be a big issue...

If you need something wider in the future (I know, don't get plastic caps in the future)-- try a quarter/1 euro coin. That worked for the old, crap caps on my Stronglight TS. Now if I could figure out how to get the super brittle, metal caps of my pedals....

http://t1.gstatic.com/images?q=tbn:A...HsgnlNkwqnd3EQ

I use to break them all the time, now I use a bottle opener similar to this one and I rarely break them anymore. When I do break one I use the end of a screwdriver to tap it out ccw. Once it's been broken they generally tap out pretty easily.

I cracked the remnants up with a needle nose pliers and pulled the pieces out.