Friday, February 6, 2015

Tandem from ... Part 1

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.

Problem #1
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.


Clearance, Clarence.

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)


Alistair said...

Impressive problem solving and tenacity. Thanks for posting this.

Anonymous said...

I have a similar tandem frame which I have been unable to absolutely identify the maker. There is a head tube sticker that says "Mountain Cycle" which I don't believe is original. The design is very similar to this tandem, the main differences are rear disc brake mount and no under BB brake. I'm pretty certain mine is the same manufacturer. I believe in the first sentence you may have misspelled the name, which I assume is "Arctos" but you wrote "Actros". I'm not having much luck finding info on "Arctos" or other Ti Tandems of this design & manufacture. Any help would be appreciated.

blackmountaincycles said...

Anonymous - thanks for catching that error. Yes, it is Arctos. If your tandem has a disc mount, I doubt it was Arctos as I believe his production of frames (single or tandem) was pre-disc brake era and extremely limited. There weren't/aren't many tandem builders, and fewer titanium tandem builders.

Mountain Cycles was a brand out of San Luis Obispo in the 90s, but they were primarily an aluminum suspension mountain bike maker. Your best bet to try to track down your tandem's maker is to contact Santana Tandems. They would likely be the most knowledgeable about titanium tandems.