One of the nice things about being mechanically inclined, and also working with some talented machinists is that some options open up for fixing and customizing parts on the bike.
First, the background: my FSA Afterburner crank has been a bit of a sore issue since I got my 29er, as it did not turn out to be what I'd hoped for. It was priced similarly to the new XT cranks at the time, and since I was not running the stock triple rings on either I figured I'd give up the nice Shimano shift quality for the slightly narrower Q-factor that the Afterburners have (169mm, like XTR).
I installed some Middleburn 26t/36t rings with a Salsa ring-dinger outer guard and happily rode for the '08 season... mostly. The 26t had very little clearance with my chainstay and some occasional chainsuck was really doing some damage there. To prevent this from worsening I put a cheap Vuelta 24t ring on which solved that problem and turned out to be a very nice ring (shifted nicely, ran smooth), albeit a bit heavy.
The next problem was crunchy bearings. Typical of OEM outboard bearings. I popped the seals, cleaned them and regreased well, and have been running on those to this date. They're ok, but I feel that the plastic dust caps prevent a nice adjustment from being possible. Also, the preload bolt on these cranks is made of very soft aluminum and uses a 5 mm hex key instead of the splined tool that Shimano uses. The result is that even at the very low torque used, it feels like it will round out at any moment.
This brings us to the current situation ---> not really wanting to buy a new crank, and being fairly enginuitive, I have come up with solutions to the above problems:
- Preload bolt - solution: make the tool size larger so it is less prone to rounding out. I got some help opening the 5 mm hex to an 8 mm. A side benefit is a minor weight savings of a couple grams. Not bad for increased functionality and no cost.
- Bearings - there are a couple options here:
a) buy new FSA cups (un-necessarily expensive, still crappy bearings)
b) buy replacement bearings (the trouble here, is that Enduro only makes ceramic bearings to fit the FSA cranks because FSA decided to be silly and oversize their spindle by 0.05 mm or so compared to the Shimano/Race Face standard. This does not present interchangability issues with the plastic caps on the OEM cups, but with the larger Enduro bearings that fit directly on the spindle it won't work)
c) the solution to (b): make the spindle fit Shimano spec bearings. Some 320 grit sandpaper then 1200 wet sanding, lots of elbow grease and a couple hours later I have a spindle that takes regular outboard bearings which I can get from Enduro for $12.
- a) Chainrings: I have decided I was not totally happy with the shift quality of the Middleburn 36t and the weight of the Vuelta 24t. I was going to get the 26/36 rings from the XT FC-M771 touring crank since they are matched and would shift best, but the 26t would have clearance issues, and they are not very light. Instead I will get 24t and 38t rings from Spécialités TA which are very nice, and though they are not matched 14t gap combined with my Shimano SLX compact (M667) front derailleur should shift well. (as a side note, though heavier than XT or XTR the M667 derailleur solves a tire clearance issue that regular derailleurs have with larger tires on my bike - it's convenient that I like to run a double ring setup). To account for the 24t ring, I will be buying 11-32 cassettes when I wear out my 11-34s, which will also save a bit of weight.
Side note: in case it is not apparent, my reason for using this chainring setup is the inherently higher gearing of 29" wheels. My 29x2.25" rear tire diameter increases development by 1.115 versus a 26x2.0" tire, so 38t and 24t rings are equivalent to 42.4t and 26.8t respectively.
b) Outer guard: to go with the TA rings, I did not want to use an outer guard because it will obscure the nice chainrings from view, and is not necessary with a front derailleur to retain the chain. I also did not want to use shorter chainring bolts alone because this would leave an ugly portion of the crank spider showing. The solution is to fabricate some very light and nice looking spacers for the spider tabs:
I will update when these are done, probably in April when I am switching the bike over from winter training/Paris-Ancaster mode to the regular mtb mode with the new rings and custom bits.