How’d I Do That? Front Eccentric Gets Turned Around.

File this one under the heading of, “How’d I Do That?”

This past weekend after finishing a 25-mile tandem ride from the house I decided to chase down a nagging clicking sound that would surface when climbing or putting a big effort into the drive train.  When I say chasing what I really mean is trying to eliminate potential sources one step at a time since sounds on a tandem are quite often not coming from where you might think they are.

Case in point was at the Georgia Tandem Rally where everyone around us was certain we had a bottom bracket creak in one of the three bottom brackets on the triplet. Turns out, the noise was originating at the rear-most seat clamp.  Another friend had a creak that sounded like it was coming from the frame at GTR; however, it was silenced by tightening the quick-release lever on the front wheel.  Go figure.

Getting back to our Calfee and its clicking sound, I decided to do my best to rule out the bottom end of the drive train by pulling the cranks, bottom brackets and the eccentric, then checking torque, cleaning, inspecting, reinstalling and re-torqueing all of the fasteners including the chain ring bolts.  So, working through the process step-by-step:

  1. After rolling the sync chains off the timing rings and using a quick-link to remove the drive train…
  2. I removed the four daVinci cranks, all of which are attached by self-extracting bolts to Phil Wood Mag/Ti JIS square taper bottom brackets.
  3. The cranks looked fine and all of the chain ring bolts were still holding their torque.
  4. I verified the rear bottom bracket’s left-hand adjusting cup was holding torque and the square taper spindle was rotating smoothly and without any play.
  5. I went to verify the front bottom bracket’s left-hand adjusting cup was still holding torque and was surprised that it moved… a lot. In fact, the amount of movement defied logic until I had an “aha moment” and realized the bottom bracket and eccentric assembly was inserted backwards.

Sure enough, the left-hand adjusting cup was reverse threaded. This is only something that could happen on a tandem with an eccentric bottom bracket as it requires the bottom bracket to be reversed.  As to how I got the eccentric turned-around backwards… I’m clueless.  Worse yet, it appears as though I must have had the eccentric apart since the adjusting bolt was also reversed.  It was an easy fix and thankfully the Phil Wood bottom bracket cups on both ends were properly torqued to where they didn’t get back-threaded by precession, aka epicyclical fretting precession.

It was an easy fix in that all I had to do to correct what was clearly something I’d screwed up the last time I had the eccentric out and disassembled for cleaning.  So, in a matter of moments I pulled the eccentric out of the frame, loosened up the clam shells so I could flip the expander bolt and wedges 180 degrees and then re-inserted the whole shebang in the frame the correct way.

cannibalsAgain, it’s one of those things that really makes me scratch my head as I really had to expend some extra effort to flip the eccentric’s expander bolt and wedges around in order to make this mistake.  Moreover, there’s a scuff mark on the left side of the eccentric from my belt-drive experiment that I should have noticed was on the right side of the bike. I amaze myself from time-to-time. Regardless, everything is back together as it should have been in the first place and with any luck at all I will have also vanquished the clicking noise in the process.

While I had the bike in the stand I also took a moment to adjust the front derailleur as it had started to exhibit a little chain rub in the 53/13 – 53/12 – 53/11 gearing combinations.  Also not quite sure how that would have gone out of adjustment but suffices to say it’s all better now.

Bottom Line:  Tandems… I’ve never owned one that didn’t demand a little attention every now and again.


About TG

I've been around a bit and done a few things, have a couple kids and a few grandkids. I tend to be curmudgeonly, matter-of-fact and not predisposed to self-serving chit-chat. Thankfully, my wife's as nice as can be otherwise we'd have no friends. My interests are somewhat eclectic, but whose aren't?
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