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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 03-19-13, 06:38 PM   #26
Ritterview
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You might learn something...
TG, I was hoping to learn something from eccentrics from you. Is the Bushnell the ne plus ultra of tandem eccentric design, or do you see any possibility for tandem development of a two-piece design as in the Niner Biocentric II above?
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Old 03-19-13, 06:54 PM   #27
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Calfee's eccentric is sub-optimum, to be sure. Even with the refinements that have been made since the first ones, it remains a problematic design for several different types of bottom brackets.

Any of these eccentrics that use compression are fine so long as you are using the newer types of cranks with integrated axles and either outboard to BB30 type bearings. However, they will all be problematic if they are used with a square taper, ISIS or Octalink BB, i.e., they are not backwards compatible. It's just a data point, not a criticism.

Frankly, I don't know of a perfect eccentric; they all have the subtle nuances and issues. If you can learn what they are and master them (or find a replacement to master if the issues with the original are insurmountable), you won't spend much time messing around with your eccentric. In which case it will only become an issue when you eventually go to loosen and service it, which is when they tend to act up.

The only "better mousetraps" that I've seen are the Bike Friday Family Tandem approach borrowed by Rob English for our BF-brethern Ryan & Amy's Ti tandem down under and a really artful approach by Dave Boehm on his very custom Bohemian tandem that took the People's Choice Award back at the 2007 NAHBS. Of course, better is relative. They were very unique approaches that demand a little more open-mindedness on the part of the owners and the Bohemian design probably wouldn't work with the newer BB / crank designs.

Me, I like the expanding clamshell design that Dennis Bushnell came up with and patented and have said so since taking delivery of our Erickson Signature tandem back in 1998. All but one of the tandems we've owned since then has used a Bushnell eccentric. However, and as previously noted, I've had to help friends rid creaks and squeaks from their Bushnell eccentrics when they neglected to find out how to adjust and maintain them and as much as I've mess around with the Bushnell's I've explored the limits of the torque specs and stripped a couple wedge bolts on our Calfee's Bushnell eccentrics.

Again, even the best ones aren't perfect unless they can remove "human-induced factors" from the equation.

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Old 03-19-13, 07:00 PM   #28
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TG, I was hoping to learn something from eccentrics from you. Is the Bushnell the ne plus ultra of tandem eccentric design, or do you see any possibility for tandem development of a two-piece design as in the Niner Biocentric II above?
I was writing my last reply as a compilation entry while you posted this question. By pure luck I think I may have addressed it in a couple of the themes I shared. Again, these are just my views.

If you bound the eccentric design to a crank design and interface you can probably come up with a pretty good solution. The Nine Biocentric II looks OK, but looks don't equal perform well in practice. After all, there was apparently a Biocentric I... so therein may lie some developmental lessons learned.

Frankly, simple work pretty well too.

As much as I like the Bushnell design, I must say that the Co-Motion "four cam" design is pretty darn good too and far less prone to some of the potential torque-related issues that can plaque Bushnell eccentric users who aren't into torque wrenches, torque specs, and the like. Even then, you can still run the risk of stripping some bolts and other issues with the Bushnell models if there's any elasticity in your bottom bracket shell... which has been the case with our Calfee shells, both with and without the aluminum sleeve.

Heck, as bad as the older Cannondale models were, we all figured out how to make 'em work...

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Old 03-20-13, 06:24 AM   #29
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When we had a Comotion we had some creaking issues as well. I emailed Comotion to ask what the max torque allowed on their eccentrics and was told that were no specs on it. Oh well some grease every once in a while solved that problem. Just a periodic maintenance issue.

Now that I have adopted TandemGeeks slightly slacker Sync chain approach that allows old school chain removal without loosening the eccentric I find I like the old Santana eccentrics. Set it once with two set screws in the BB and it stays put and has never creaked. Only maintenance in 12,000 miles is once a year remove and grease to prevent corrosion. Just like a seatpost set and forget. That old simple eccentric design is pretty light too at 182 grams about half way between two Bushnell designs.

http://www.bushnelltandems.com/eccentric.html

If you adjust a lot then the design has its issues. Everything is a tradeoff but very simple is nice. No moving parts other than set screws. Number 3 in picture below.

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Old 03-20-13, 10:02 AM   #30
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TG, I was hoping to learn something from eccentrics from you. Is the Bushnell the ne plus ultra of tandem eccentric design, or do you see any possibility for tandem development of a two-piece design as in the Niner Biocentric II above?
Thing is, BB30 itself still has a list of issues around fit induced noises... clicking, creaking, etc. I am not sold on the idea that pressfit components belong in the BB, at least in their present implementations. Likewise with trying to provide a stable eccentric by clamping it to the side facings. Building upon that design at this point, to me, would seem to lend itself to compounding the problem.

Expanders and cams have their own set of design issues to overcome, because every crank stroke induces loads against those same expander wedges or cams.

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Old 03-20-13, 10:05 AM   #31
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I find I like the old Santana eccentrics. Set it once with two set screws in the BB and it stays put and has never creaked.
The only issue I had with Santana's grub screws was their tendency to index if you tried to be more precise than you needed to be in the adjustment of your sync chain tension and, well, the marring that naturally came from and contributed to the grub crew indexing. Suffices to say I was extremely anal with our first tandem back in '97 -- a Santana Arriva -- so I probably made more of it than it warranted.

Co-Motion is interesting in that they have a constellation of eccentrics on their tandems; it's all rather intriging and I'll have to ask why they haven't adopted just a single design at some point.
- The pinch bolts used on almost all of their tandems before 2005 and still used on some models was one that I never really liked: something about putting a split in the eccentric shell just seemed less than optimal and those were indeed prone to creaking if those two pinch bolts weren't torqued and secured with Loctite.
- They also have some bikes out there with the grub screws, but use four vs. two. Again, about as simple as you can get without using a split eccentric design.
- The newer eccentrics use on their steel tandems and at least the ones installed on an aluminum triplet that I work on now and again with the "internal binding system" are pretty slick and the ones that appeal to me. There's a nice balance there in terms of simplicity and elegance.

Again, all of these different designs work, but sometimes there's a bit of a learning curve to mastering their nuances to achieve a quiet ride or to make routine service a non-event.
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Old 03-20-13, 03:37 PM   #32
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Oh good, another forum member trashing my post. So thrilling. Look: we own a davinci bike. It had a davinci eccentric. Based on what a very reputable shop told me (which has on staff/management the designer of the part), the eccentric wasn't making full and proper contact with the frame. Right about now, I don't give a darn about friction: the eccentric and frame were from the same company, and they couldn't figure out how to make them meet in the middle! Explain to me why I should call them to find out why, and explain to me why I should stop for a moment to consider the friction forces and such.
Oh, and by the way, you have a typo in the beginning of your post. There are no principals at play here, we aren't in school. In school, I learned that these were principles. And before you flame me for being anal-retentive, consider that accuracy in word choice is essential to any sort of technical explanation, which you were trying to do.
P2; Sharing the pain... I have gotten a few head slaps for not being quite politically correct about the greatness of CF or arguing agains low spoke count wheels or other crap.

But to your current posie. If I had to ponder such, I would say that 60% chance the ECC shell ended up warped just a bit during the orginal build or from someone over torguing the insert when the insert wasn't quite in the straight at the time. I have seen both problems and both pi&&ed me off at the time.

You may be able to prove if yours is or not by taking a lot of ID measures on both sides with a digital caliper, If it is not round, then it'll show up. If it is warped along the length, i.e, twisted it probably won't but an eyeball exam to aid a metal straight edge inside the shell might. There may be a reaming tool for the shell -- something like 54 or 57mm, but I haven't seen one myself. Recommend reading all the related spittle on the www.Rodbikes.com site and then call them to ask if they have a short list of issues they have found with that brand (I think they quote having replaced a ton of them with their new Bushell versions to "a high degree of success"). Although the Rodbikes guys do have a tendency to advocacy on some topics, I have never had to them not be willing to discuss an issue and share what they know or have experience first hand with. If they can narrow it down for you, it might just be a matter of $125 or $150 bucks to set it straight. I know I have had great luck with their EC inserts and their EC shims as I have come across a number of 2bike and 3bike frames that were stripped down for flipping and the parts lost or that had most of the tandem unique parts seriously buggered up due to inept maintenance/repair attempts (like the early Taylor 2frame found about 20 years ago with rounded pieces of 1/4" plate brazed into the ends of the ECC shell and drilled/tapped to fit Italian BB cups. But the threads weren't in-line between the two sides (about a 1/16" off). After the owner killed expensive Campy BB bearings and cups about 5 times he gave me the frame for the $50 down payment for me to build him a new custom frame that looked just like the original (I thought I would die before I got all the box lining on right). With a weekends work I was also able to right the old boy and move it on to a collector in serious pant for one (and he had enough coin to make the deal [

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Old 05-28-13, 11:53 AM   #33
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We had an interesting case of "the ticks" this last weekend.

Any abnormal bike noise drives me nuts, so during a mid-ride stop I checked out the usual suspects and found the EBB bolt had become completely loose and spun freely. The EBB had not budged during that +18mi stint, so it appears the 2 internal wedge blocks stayed put regardless of the bolt backing off. After tightening the bolt the tick noise was gone, so this confirmed the root cause.

AFAIK, typical maintenance instructions for this type of EBB are to grease this thing thoroughly, especially the wedges, but I'm thinking maybe some blue lock-tite on the bolt threads might be a good idea.

Anyone have a similar case and solution (other than tightening the bolt more firmly)?
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