Only a couple years in the making, this Arctos Machine titanium tandem made by Merlin co-founder, Gary Helfrich, is owned by a local resident. I'm guessing it was made around 1990 and had most of the original parts on it when I brought it into the shop a couple years ago. The task was to install modern road components, converting it from a flat-bar bike to a drop-bar bike.
Because one of the parameters was a triple crankset and integrated brake/shift levers, that narrowed things down to Shimano. The R601/R603 cranks are an interesting design. The stoker's crank is mix of Ultegra 6700/Dura Ace 7900 aesthetics combined with an axle design like the XTR 970. A kind of Octalink/Hollowtech design. This is where I ran into problem #1 and #2.
The stock front eccentric bottom bracket is not threaded, it utilizes pressed in bearings and square taper axle. This requires a new eccentric bb. Problem #1a - the diameter of the eccentric is a one-off part and does not match any available eccentric sizes - by a long shot. From my product development days working with Taiwanese vendors, I knew that Tien Hsin/FSA made several eccentrics of various sizes. I found one that was close (a little oversized) and sourced it from Taiwan. With frame and new eccentric in hand, I headed to Petaluma, CA and the shop of Sean Walling's Soulcraft Cycles where he chucked it up in his lathe and turned it down to fit perfectly in the old frame. Big thanks to Sean.
Back at the shop, new eccentric installed, time to install the cranks. (Expletive and problem #1b) The stoker's crankset chainrings don't clear the chainstays or the rear, chainstay mounted WTB Speedmaster roller-cam brake. Hmmm. Don't panic. The stoker crank design is such that it requires spacers (supplied w/crank) under the left arm to set the arms just so against the bearings. Instead of installing the spacers under the left arm as the instructions dictate, I installed some under the right arm and some under the left arm to get me the chainring clearance needed on the right side. There was still an issue with the left side, but it's way easier to deal with this issue on the right side. The right side was dialed and chainline was still ideal - the left side, however, problem #1c.
Initially, the problem with the timing chainrings was the chainring bolts were a bit too close (touching) to the brake arm. A combination of filing a bit of the corner off the chainring bolt, changing the 42t rings to 38t (the smallest that will fit to a 130mm bolt circle), and filing a bit of the brake arm got everything to play well together with good clearances.
Making clearance with the file
Some of the tools used to get the cranks installed.
No clearance here - time to improvise.
The original eccentric used a double bearing on the left side - good idea.
Filing the brake arm for clearance
Checking clearance - only want to remove just enough.
The 38t rings helped, but not enough.
Stoker operated drag brake cable routing
The bike also got a new wheelset build with Chris King hubs with a stainless drive shell.
All should be good to go, right? Wrong. Problem #2 rears up, but that will be in Part 2, which I'll try to get to soon as it's deserving of a separate post.
(What's playing: Blondie Dreaming)