Dustcap From Hell
 

This could just as easily be posted in the Mechanics forum, but I thought C&V would get a kick out of it. This was my first day in the shop with an '85 ST 500 frame that had a few of the stock parts still attached, including the bottom bracket, crank arms, rings, headset, fork, and stem. I already had a difficult time with getting the siezed stem out of the fork...little did I know that the crank arms were going to be even harder.


Lest you wonder why threaded parts ought to be greased, wonder no more. Witness the carnage wrought of a 27-year-old aluminum dustcap on an aluminum crank arm:


The hex hole stripped almost right away when we tried to unscrew the cap. Nothing we did to get traction helped. So the Dremel came out to try and either snap the threads at either end or make a slot for a screwdriver.


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The slot worked for the drive side of the Shimano 600 cranks. Not so for the non-drive side.

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A total of seven hours of hacking, chiseling, Dremel-ing, drilling. I broke the tips off of two flat-head screwdrivers, went through five Dremel cutting wheel heads, wore down a drill bit, and we still couldn't fit a socket in there to grab the nut. If you look closely, you can see that the threads have BONDED TO EACH OTHER. Damn aluminum and its free-flowing electrons...

http://bikeforums.net/attachment.php...hmentid=250295 http://bikeforums.net/attachment.php...hmentid=250296

We came to the sad conclusion that the non-drive-side arm was a goner. Hacked and scratched from drills and Dremels and screwdrivers, we still would have had to re-tap the threads even if we were able to somehow reach the nut. So we decided to cut through the spindle (also a shame, as it was it quite nice shape), and at least save the rest of the 600 EX bottom bracket.

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Just a tap of the hammer, and it was all over. The crank arm was warm to the touch for the next half hour!

So please, kids, make sure to grease your aluminum dustcaps at least once every, say, 10 years or so. Or for Pete's sake, just get plastic dustcaps that can break off if need be!

Jobs like this take patience... penetrating fluid and time can work wonders.

Barring that... WD40 and a torch in a well ventilated area can also do wonders.

Spray the WD40 into the seized part and then heat it with the torch being careful not to burn the frame, cable housings, or yourself... the heat causes the WD40 to burn off and in doing so can often break the hold those parts have on each other.

Have used this on small jobs and for extracting 3 inch bolts from oilfield equipment that might have been in the field for months or years.

Sadly, the shop where they're letting me work on this bike doesn't have a torch license, though the use of one came up repeatedly in problem-solving discussions. Once we got a look at how much these threads had bonded to one another, however, it's possible using a torch still may not have worked. There were a few sections of the thread where it had simply become one big blob of aluminum; absolutely no separation between the threads at all. Not even anything for WD-40 to work itself into! CleanStreak was applied liberally before any drastic measures were taken and worked on the drive side, but not on the other.

Also, I was nervous enough using both a Dremel and an angle grinder for the first time in my life in one day. A torch might have put me over the edge!

And anyway, I'm going on tour in less than two weeks. Gotta get 'er done! ;)

What good shop doesn't have a disposable propane bottle and a benzo torch head ?

Imagine yourself the proud owner of an '85 ST 500 (is that a Black Lightning?). You drop off your bike for some BB servicing or some such work. Couldn't ride today because the bike is in the shop. So you just log onto the bike forums and get the 'ol bike fix in. Hmm, dustcap thread...could be interesting...hey, is that my? MY?! OH, THE HORROR!!!

wow-
why do people go for death when all it take is patience and/or the right tool.

OK the cap was shot, a modern heatgun will do wonders

penatrating oil and time

tapping on the cap to try to crack the corrosion

using dremel to cut a slot thu the threadwall of the cap and then getting it out

if the threads were usable..

heatgun the arm for 5 minutes and try the puller.

if the threads are shot- the arm is gone-destroy arm and salvage axle

drill a series of holes across the crank arm use a chisel to crack it

you would have saved the axle..

heatgun is a must for a bikeshop!

I think that this is the OP's bicycle.

Seized dust caps can be a royal pain but I have yet to be defeated by one.

If so, I missed that.

I just came from checking out Drillium Dude's dremel handiwork and it was a bit jarring to see those dremel scars on the crank arms. I felt bad for them. Maybe a file or saw on the remnants of the cap, say around photo #3, could have saved the spindle. Patience, penetrating oil and patience pays plenty.

I found this an easy job. I bought a bike with a dust cap already totally rounded out so I gently tapped in a Torx bit a fraction larger than the hole and it came undone easy it all so keeps the cap undamaged and useable.

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This would have been a very good time to check for a loose fit of the adjustable cup (with the lockring pulled, of course). You might have been able to pull the whole unit out and saved yourself some time (though junking the spindle and LH cup in the process).

-Kurt

Yup, this is my bike, so I'm ok, though sad, that we had to resort to this. I'm changing to a triple anyway, so the stock double spindle was just going to be given away if it could have been saved.

No torch in the shop because I believe getting a license in NYC is a royal PITA, and they don't get enough requests to warrant the cost. Yes, I could have found a shop that has a torch, but these guys have been great to me. Would have been nice to try, absolutely. I'd still be afraid of hitting the BB or the frame, though.

Torx bit was attempted, and just caused further rounding :(

We were thinking of cracking the crank arm and trying to save the axle, but again, I was the one worried about slipping and hitting the frame. I'm not a pro, but I'm learning as much as I can. I'm more or less doing this myself as my first build ever, and the shop is being kind enough to loan me a stand and advice when I ask for it.

We had 3 full days of work at this dust cap before we finally resorted to these measures. We were incredulous that a simple dust cap was killing us, but I do think that not even a heat gun and more patience would have helped in this case. After 27 years of metal on metal, the crank arm threads and the dust cap threads had bonded completely. When we were chiseling and filing away at the edge of the cap we were sure we'd be able to pull off the threads when we hit the edge. But when we got there there were no threads to be seen...it looked as if one thread had melted into the other, like a piss-poor weld!

All in all, I'm happy that at least the DS arm and the entire BB could still be saved and can be donated to someone. This is what I get for getting excited by poor condition frames on NJ's Craigslist, but I'm happy with this project and can't wait to restore it as a tourer/commuter. It was certainly an interesting chemistry lesson that metals are always able to exchange electrons to the point where, after nearly 30 years, they've essentially welded themselves to each other!

I had a run-in with a chrome plated plastic dustcap that nearly got the best of me, so I can imagine how much of a nightmare a seized aluminum one would be. I eventually picked all the bits out and saved the extractor threads.

Having said that, since the DS arm came off, I would have cracked the lockring and removed the NDS cup, then tossed the lot into a bucket of Kroil to soak for the duration of the tour :)

This is exactly what I'm going through on an '87 Circuit I bought last month. I'm avoiding working on it anymore in hopes of not having to ruin cranks. Maybe this weekend I'll give it another go.

Torch: Propane or maap gas. All it takes is a few seconds blast to expand the aluminum. It also works well for removing stuck crankarms, if you think the extractor is going to strip the threads blast the arm for few seconds and it'll come right off.

Seen similar aluminum fusion-like problems at the threads with BBs for sale at ebay, where the inner most threads on the BB cups had been left behind in the BB shell when the cups were removed.
Never experienced such, but I guess it happnes enough.

Chombi

Plastic caps can obviously be melted out with a propane torch.

For the metal ones that have gotten stuck like the OPs I use a small, narrow chisel and a few different drift punches and lots of patience.

And like Sixty Fiver I've never been beaten by one and I've never destroyed a crank arm getting one out.

At least it's done.

I've had to dremel slots in a couple dust caps. For one I had to chisel / break the plastic to clear the threads. One time I stripped the threads and had to cut the crank arm. One cut was enough to free it.