Tandem Cycling - need help -- eccentric issue

I have a 2008 Co-motion Speedster. Today I noticed the chain was just a tad loose so I went to adjust the tension. There are 4 little 4mm allen screws that hold it in place. When I went to loosen the top left one it was a little tight and long story short when I went to loosen it I broke the little ball on the T-allen wrench in the allen screw.

I knew better to use the ball end of the wrench but had a mental lapse.

Any ideas how to get that out of the allen screw??? it is loose (as in it moves a little) but will not come out --so far.

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second question assuming I get it out where can I buy the little allen set screws as a replacement

thanks

Mike

I'm assuming it's wedged in there, I'd probably try something like this

Again, if it's wedged in there you should be able to drill out the center without touching the allen screw. Once it's drilled-out, and assuming it didn't come loose in the process, I'd thread in a small easy-out / screw extractor which I'm guessing would do one of a couple things:

- split the thing open.. at which point I'd back out the extractor and pick the pieces out of the screw head.
- bite and twist the hex head loose
- bite, but not twist the hex head loose... but give me enough leverage to work the thing loose.
- bite and unscrew the allen head screw with the t-ball still wedged-in the thing.

As for replacements, call Co-Motion or Tandems Ltd... I'm guessing they'd mail you some in an envelope at little or no cost. Other than that, if you had a really good distributor like Screws of the South (located in Marietta, GA... thank you very much), they'd probably have the correct size & pitch on hand.

try a little bit of super glue on the end of the broken allen wrench, glue it to the ball head that is stuck. might just give you enough "purchase" on the piece so you can get it out of there.

try a little bit of super glue on the end of the broken allen wrench, glue it to the ball head that is stuck. might just give you enough "purchase" on the piece so you can get it out of there.

Low Tech meets High Tech, great idea. Seems just a drop will do to prevent gluing it in place.

PK

If the ball is somewhat loose you might also try and see if using a strong (rare earth) magnet will help pull it out of the head. Assuming of course that the T-wrench is made of steel.

.

Sorry, I cannot agree with TG, tho I usually do... the allen "ball" end is too hard to drill. Do whatever you can too get the piece out
Rod

So far no luck.... tried a drop of glue (to no avail) tried drilling (nope -- broke several bits) not a good situation.... may have to try to drill the whole allen screw out and replace the eccentric.... arrrrgh

any other ideas??

Sorry, I cannot agree with TG, tho I usually do... the allen "ball" end is too hard to drill. Do


tried drilling (nope -- broke several bits) not a good situation....

It was a long-shot, and it assumed the broken-end of the wrench would be a bit softer than the exterior. Also, you would have had to use very good HSS drill bits with carbide or TiN coatings. Even then it takes a lot of patience, oil and care not to break the bits when drilling on hardened steel and, well, drill bits that are harder than the steel. If the hex-head wrench was a good one, then no way... but, then again a good one shouldn't have broken.

The only other way to get it out is to bugger-up the softer metal of the hex head eccentric screw as you pry the broken piece out. After that, it's the same as I described in my first post. Drill out the allen head screw in the eccentric and then use an easy-out.

I'm going to suggest finding a local machine shop and let them get it out. They usually have lots of experience in extracting stuff like this and have all the right tools. May cost you a few bucks but probably better than making a bad situation worse!

Roland

Could it wait until the Vero Panthers ride if you are going? Get some replacement set screws from Co-Mo and I can bring some of the aircraft and exotic drills, plus a Makita and some extractors. I also have a carbide setup I use to remove broken taps and easy outs from fasteners on the aircraft.

You could always box it and send it here too, not sure how much frame it would be uncoupled.

PK

As a Mercedes Benz technician for over 22 years [and BMW before that] I have seen many of techs break the 'ball' allen wrenches. The reason it is broken is the torque used to turn it [duh]. So it is twisted in the allen head and it will not come out without twisiting it back. I have been known to 'butch' things apart and the best way is to tack weld something to the head of the ball. Sure the head is small and it takes a good welder and a good hand. Sometimes a very small punch knocking it the opposite dirrection may get the ball loose. Drills are not the way to go. The bolt is softer than then the broken tool head. You'll just make things worst [including your attitude]. Glue, that will not work either. Grinding may work but you will need a very small grinder [Dremel] and a sharp cutter. Cutting the bolt head may be an option. Most of the new techs I know usually break one, no matter how much you tell them not to turn too hard. Spending the time to cut away the head of the bolt and not the broken tool is an option that may work. Once the ball comes off then drill the head off the bolt and of course replace the bolt.
One last thing, If you can do the job without loosening the bolt, then leave it alone and worry about it later [or maybe never]
The good thing is that you will never break another one. Your new found experience will make certain of this. Good luck and spread the word, Do not use ball allens [unless there is no other choice].
At least you are not working on a $500,000 Gullwing or SLR. It will all work out, trust me, it always does.

Did you try to loosen and remove the other three fixing bolts to reduce the pressure on the one with the broken allen ... with three out, you may even be able to remove the eccentric, making it easier to extract the one with the problem.

Sillly question but Is the screw recessed? Or can you get a vice grip around the head? Another thing that might work is if you tap the head of the bolt with a punch and hammer, LIGHTLY, just enough to send vibration thru the threads to help free it up, next cut a slot in the top using a dremel, thru the ball end and all, then use a slotted screw driver in the slot to unscrew it. The tapping with the punch should allow it to break free without too much force. You,d be surprised, sometimes a good several taps with a flat punch makes a bolt that would otherwise be impossible, crack loose easily. good luck with it.