Stuck eccentric BB (Trek T100)

[truckin]

Hi all,

I've been reading a number of different forums here for some time now, and I've gotten a huge amount of useful information from everyone. In fact, I found my first tandem through this very forum. It arrived last week, and my brother and I have built it up (we're fairly knowledgeable and handy; brother worked in a bike shop for a while as well). We've got all the standard tools and were able to get everything going well with one exception: the eccentric BB. The tandem is a Trek T100 (I know it doesn't hold a candle to the higher-end tandems out there, but it's in our price range and we're big enough to make it roll at around 190 each and pretty strong).

First off, I want to make sure that I understand the proper adjustment for this eccentric. On the side away from the timing chain and rings, it has a large hole for a long bolt that extends essentially through the entire width of the eccentric. There are four smaller holes (only about big enough to fit a 2.5 mm hex wrench into); they are called rotator holes according to my Google research. They are only about 1/2 to 3/4 inch deep. Two of these are before the large hole and two beyond it, following an arc around perhaps 1/3 of the circumference of the eccentric's face. According to repair procedures I found via Google, the recommended procedure for adjusting this type of eccentric is to unscrew the large bolt a few turns, insert a hex key into one of the rotator holes, and rotate the eccentric to the desired position. Sounds quite easy, but...

Having attempted the above, it will not be as simple as that. I believe the eccentric is frozen into position. It's aluminum, and of course it's in a steel frame; so I'm guessing that I have an aluminum/steel freeze on my hands. I tried a Liquid Wrench application to the seam between shell and eccentric, but that didn't do me any good. I also applied moderate force via a rounded-off screwdriver and a hammer, but the eccentric still wouldn't budge.

My questions then are:

Is there anything I don't know about how to adjust this type of eccentric (i.e., I'm not loosening something that I need to loosen before doing it)?

What suggestions might you experienced tandem riders/wrenches have for this problem? I've heard of the ammonia bath and am willing to try it but would like to exhaust any other possibilities prior to resorting to it.

Apologies in advance for cross-posting; I'll lay this out in the mechanics forum as well, but thought it likely that someone out there in the tandem world would have some ideas I might not get from that forum.

Thanks for all the knowledge I've gained while reading the forums, and thanks in advance for any light you can shed on this dilemma. Hopefully I haven't made any unforgivable newbie mistakes!

[TandemGeek]

Trek used a wedge type eccentric for its tandems and it often times takes a little brute force to get the things apart.

The textbook service procedure is to back out the eccentric bolt to expose the head and then to tap it with a mallet to release the tension between the eccentric and the wedge. However, the most often cited removal methods from those who've owned the older Trek's include:

1. Remove the eccentric bolt and temporarily replace it with another, longer bolt that has the same thread pitch and diameter and thread it as deeply as possible into the wedge before hitting the bolt head with a hammer to drive out the wedge. Note: the tandem frame must be braced by a helper otherwise the bike will move with each hit, lessening the driving force.

2. The less brutal method involves placing a lever between the bolt head and the crank arm and using the crank arm's rotation to drive the lever against the bolt head and forcing it in. You only need to have about 1/2 of the eccentric bolt head extending from the eccentric for this method to work. Cresent wrenches (aka, spanners or adjustable wrenches), hammer heads, and other solid objects have been listed as "levers" in previous descriptions that we've come across.

As for those "rotator holes", you can usually rotate the eccentric with your fingers once they're loose. However, if you need to have added leverage you'll want to pick up a Park SP-1 pin spanner (Green Handle).

[truckin]

Thanks very much, TandemGeek. I'll have my brother give it a try as soon as he can, and I'll report back on our progress (he has the bike in VA; I'm in NC for the next few weeks).

[truckin]

TandemGeek-

I had my brother try the "whack it with a big hammer method," and it broke the wedge free very quickly. He's pulled it out now and will reassemble it with anti-seize and the proper amount of tension for the chain we put on it. Thanks again for the information; I think we just needed to know it was OK to beat on it a bit!

[LV2TNDM]

If the bolt hole in the wedge extends all the way through the barrel nut to the other side of the eccentric like on Cannondales, then a another method works well. I recommend this as I've heard of the (rather long) eccentric bolts being bent by the forces of hammering on them.
Unscrew the eccentric bolt to the point where it's just about to unthread from the barrel nut. Screw in a shorter bolt from the other side - once it threads, remove the long eccentric bolt. (this prevents the barrel nut from moving, which would make things rather bad - you may not get the hole in the nut to line up with the bolt again!) The screw from the other side should be threaded through a backing plate (the hole in a headset wrench or cone wrench works great). With a few washers and lube, screwing the bolt into the wedge from the other end will pull it free as the backing plate bottoms out on the BB shell and/or eccentric. I carry an extra long water bottle bolt & cone wrench on trips so I can adjust timing chain tension anywhere. No need for a hammer and brute force!

[Maury Cohen]

Our method for eccentric adjustment is to place the end of a screwdriver or long allen tool into the adjustment hole and using the leverage of the crank arm to spin the eccentric shell into proper tension.

[RJ_Mettlehorst]

Great suggestion on pulling the wedge out from the left side instead of whacking it out from the right! I'll definitely try that.

That leads me to two questions: First, do people prefer slathering things with grease, or a coating of automotive-type anti seize compound? (I use 3M High-Temp brake & engine compound - copper colored) My personal first instinct is to use anti-seize, but I have to be a bit more careful with the torque - it is a far better lubricant at high pressures than ordinary grease.

Second, what is an appropriate eccentric BB wedge bolt torque? How tight is required? I'm thinking the forces really aren't tremendous, but it has to be tight enough to keep the chain tension and not creak under heavy pedaling. Does anybody have a numeric value?

[JoblessDave]

I have a Trek T-2000 and I just went through this. I was hammering on the wedge bolt with no result, and finally took the bolt out, passed it through the small hanger hole in a headset wrench, and screwed the bolt in from the opposite side. As soon is the bolt started to get tight the wedge puled right out. Easy as cake.

[zonatandem]

Trek and C'dale seem to have this wedge-type eccentrics that need 'hammering'.
Older styles had exterior bolts to loosen the split bottom bracket shell made life much simpler.
However tandem design has evolved to no more split bottom bracket shells for eccentrics.
Bushnell type eccentrics pose no such issues.

[cyclesteve]

I have not had a problem adjusting my eccentric. I used the remove the eccentric bolt and replace it with a longer bolt method. Can the Trek eccentric be replaced with the Bushnell type?

Steve

[bikeriderdave]

There was no need to go through all that with a T2000!!!! The improved design eccentric couldn't be easier to loosen and rotate. Just turn the wedge bolt CCW ("lefty-loosy") against the "keeper" nut, and the wedge will loosen. Then, insert the same 5 mm allen into one of the broached hex holes and turn the eccentric to the correct chain tension. Finally, re-tighten the wedge bolt.

[bikeriderdave]

Trek eccentrics have NOT required "hammering" since the improved design was introduced on the first T1000 and T2000 in 2002. Split BB shells are not practical on an aluminum frame, as the shell will distort during welding and/or heat treat. Trek BBs are machined to the correct ID after artificial age, which is why they adjust so nicely. I have had NO trouble adjusting our T2000 eccentric. As I said in another note, I don't think it could be any easier.