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.

guillmunozSFO

I have a Tandem Trek 200 with a Shimano Concentric BB and probably the original OEM that came with the bike - it is still in very new condition as tandem tend not to be overused. I had a hard time loosing the concentric BB, even after reading all the recommendations above. After confirming pounding the bolt with a hammer from the drive side didn't do any good, I decided to buy a shorter bolt and loosen the plates from the timing side - the threaded hole that hold the plates together goes all the way through to the opposite side. On my first attempt, I simply loaded the bolt with multiple washers and attempted to loosen the concentric - no luck, nothing move a single mm. After thinking overnight, I realized that simply using washers was not providing the leverage required to loosen the plates and found a cone wrench that indeed had a perfect sized hole that I could use by placing it over the "FRAME", giving me the leverage needed to do the job - and that did the trick. No pounding, no trouble. I was then able to easily use the Park Green Pin Spanner to loosen the concentric and remove the chain for cleaning. I hope this helps another soul keep the OEM components going. Thank you LV2TNDM

preventec47

This is a great collection of wisdom as I have a no name aluminum tandem frame from about 2000 and when the stoker chain got real loose I tried to
adjust the eccentric (sp) in the main crank area to tighten it and I could not move it. I just wound up buying a new unstretched chain to solve the poblem.
Maybe someday I will be able to break it loose with the info here. I fear dis-similar metal corrosion between the aluminum frame and the parts will act like glue stronger than a weld.

tmkboston

So, I destroyed my Trek 100 Double Track Tandem eccentric trying to get it out. And now I need a new one. Does anyone know where I can get one? Are they standard sizes? Or do I need to find something specific?

Paul J

I'd call Mel at Tandems East. He has stock in pretty any eccentric/bottom bracket version. 856-451-5104 Their website is www.tandemseast.com

tmkboston

You pegged it, Paul J! Thanks! Mel is shipping me a 57mm EBB!

BikeTim42

Care to share the mistakes you learned from while destroying the old one? (might keep me and others from doing the same)

BikeTim42

I know this is an old post but do you know if the eccentrics in the MT2000 from '94 are of the newer retention design? Or how to identify it? I'd hate to back out the bolt too far trying

base2 

For future reference: Pounding on the wedge bolt from any direction by any method carries the risk of blowing out the soft aluminum threads.
Hitting the shell away from the wedge can/may be a more effective strategy.

I second the Bushnell idea.

BikeTim42

I may have answered my own question with a bit more digging. It appears that the newer ones have an EXTERNAL circlip for the bolt to press against to push the wedge. If you do not see one on the outside, it must be the older one. (my '94 MT 2000 has the older). I think the size of the positioning holes is bigger on the new ones too including hex fitting internally instead of simple pin tool holes.

tmkboston

I don't recall all the wrong steps I took, but I believe the first mistake was being in a hurry. Second was that I thought it wouldn't cost too much to replace it (turned out to be quite expensive). Third I assumed these were standard things (wrong - the size was long retired and it took at least a month to find one, and then only because I probably got lucky). These prior reasons led me to mistakenly think it wouldn't be a problem if I had to drill the thing out. If I had known the trouble and cost to get a new one, I would hopefully had taken more time with this. Because then I loosened the screw that connects the wedge to the point where the nut rotated and I lost track of it. Which led to hammering and banging and then drilling and ultimately the thing was useless. In hindsight I should have waited until I got everything else off the bike (its own project given the age of it) and then I could have turned the bike upside down more easily and focused on the task at hand; probably using heat on the frame and tapping it out gently. I'm not sure if I'm allowed to mention companies but I found it at a place at sells Tandems on the East coast. Let me know if anyone needs more thx.