Wednesday, September 15, 2010

Techie Tuesday

Aesthetic, but not much to look at from this side - except the crank arm pin at the top that tells you how to align the 5 holes, and keeps the chain from getting jammed between the crank arm and outer ring.

You can also use this pin to get a feel for where in the pedal stroke the shifts are planned. The first shift-pin is 5 teeth back from the crank arm pin. Double cranks have their 1st pin 7-12 pins back. Note too the chainring bolt holes are counter-sunk so the bolts can directly bear torque forces.

Color is gray, despite my halogen lamp's insistence it's bronze.
Flip it over, and a world of marvels awaits you as you try to figure out how many ways all of the pins and ramps and ramp-lettes, will bend your chain to give you instant shifts. However it works, it works well!

More pins and ramps than you can shake a chain at!

It's a triple outer, and clearly stamped 52-39-30. This defines the angles the pins and ramps are designed for
I'm running 52/38/28 for now, but it looks like that is not different enough to create a problem. In fact, the 38T seems to drop the chain off onto the 28T in a way that the chain fits onto it's teeth without having to slip back to sync up.

Extensive machining and pinning make for instant shifts
An edge view showing more relief on the pins and ramps
Torx-30 aluminum FSA nut and bolt - left. Steel allen nut and bolt - right.
I broke one of the FSA bolts, tightening it without even holding a wrench on the nut, and it's clear why. The FSA nut has to devote almost half of the threaded area of a traditional nut to an engagement area for the Torx-30 driver. The FSA bolt is thus much shorter. The traditional system has the bolt go all the way through to the end of the nut, so a lot more threads can be used to tighten down the chainrings.

Add to that the inherent weakness of aluminum and it's understandable why one of the bolts broke in half. I felt lucky there was enough Torx engagement left to be able to get the broken piece out of the nut. The replacement bolts were $2 at Performance Bike Shop.

3 chainrings, 3 colors. Thank you Shi-follow marketing mavens
To get the nuts out, you have to pull the crank off, unbolt the 74BCD granny, and then turn the screws out of the bolts. Tedious, as the chain is always dirty and it has to go somewhere while you're working on the crank and chainrings.
52T from Japan, 38T from France, 28T from USA. I expect to be invited to the UN any day now!
A well-behaved mutt!
I will probably replace the TA Alize middle ring with a Shimano 6603 39T soon. The 28T is a Salsa I've been meaning to put on for 6-8 months, and this seemed like a good time. It is BEEFY! A good thing in a granny, because at 28T there aren't many teeth pulling when you are stomping and torquing up a hill, and that means they wear out fast and start exhibiting chain suck.

PS: I'd like to dedicate this post to my father, one of the best mechanics who ever held a wrench. Thanks for all you taught me. Miss you pop. Wish you were here.

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