Saturday, June 7, 2008

What's in the stand...

AKA "You learn something new every day." Had a nice fillet-brazed Mikelsen dropped off for some work a few days ago. It's that tiny bike sitting behind my bike in the post below. It was built up with a mix of Campy Nuovo Record and 6-speed Dura Ace. The owner wanted to set it up with lower gearing for his daughter. It needed to have some fairly major work done to get lower gears. The original wheels are Dura Ace 6-speed with Uniglide cogs. It would have been much easier if a 6-speed UG cassette in 12-28 were easy to find, but it ain't. UG cogs differ from HG cogs in that the splines are all the same width where as HG cogs have one spline that is wider than the others - no inter-compatibility between HG and UG.

So, what to do. He had a wheel with a newer Dura Ace hub that is compatible with 8/9/10 speed cassettes, but it was spaced at 130mm and the frame is 126mm. Not wanting to alter the frame, I set about to respacing the hub to 126mm, redishing the wheel, and cutting the axle down by 4mm. Installed an 8-speed 12-28 cassette, replaced the NR derailleur (with a "patent 72" mark) with a new 105 derailleur to handle the range better (and have better shifting), and threw on a SRAM 8-speed chain.

I knew that the 8-speed chain might make pose a slight problem with the 10-speed 105 derailleur, but didn't want to go narrower because of the spacing and tooth width of the NR chainrings. And yeah, as I suspected, the chain was noisy running through the 105 pulleys. After some inspection to see how the chain was running through the pulleys, I determined the noise was coming from the upper guide pulley.

The guide pulley floats on the bushing which is an aid in adjusting index shifting, but in this case, the float was allowing the wider 8-speed chain to slightly rub on the cage. Hmmmm, what to do. What if the pulley doesn't float? Yeah, that's it. Installed a replacement lower tension pulley (with no float) in the guide position and it immediately solved the problem. So, there you go. Where there's a will to combine a combination of brand new 10-speed ccomponents with 36 year old components that were used with 5-speed drivetrains, there's a way.

(What's playing: I think KWMR is playing something by Schubert)

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