sprockets, torsion, and…

Creaks and pings where I least expected them. I was watching the drivetrain on the 1×7 degrade into nothingness over the winter commute. The crankset was bent to the point where I could see the chainring move in and out as it would rotate. The chain had enough fore/aft movement that the deraileur would wiggle 1/2″ front and back as the crank revolved. Amazingly enough the chain was still in spec, and had only stretched .01 – .02″ per 6″ of links over it’s life.

For the past year I’ve been amassing the parts I needed for a drivetrain revamp and I had everything I needed aside from a crankset. I was weighing my options, and I didn’t want to spend much (translated any) money. First choice was to go out and spring for a new crankset. There weren’t too many options out there that I liked, and my choices were limited further by the fact that I’d be springing for chainrings  too unless I got a crank with a 104mm 4 bolt pattern. There are plenty of 1 sprocket cranks out there, but nearly all of them are 48t and geared for youngsters on track bikes. The rest cost $125 + and have a 32t offroad ring. Second choice was to take the old square taper crank I had from the no-longer Specialized and get a chainring. This is the way I went. Surly makes a stainless ring, and I figured if the crank was half as reliable as it had been for me before than that would be a better bet for a cheap combo than my aluminum rings paired with another cruddy set of arms.

I had the chainring on order while I was finishing up painting around the house last week. Once I finished cleaning up the kitchen from Easter it was tax season for me as I had put off filing for 2.5 months after my preliminary figures from February had us owing slightly this year. Monday and Tuesday were paperwork days. Wednesday the package showed up on my desk. I had parts, and for the first time in 1 month, a free evening since it was raining and I couldn’t cut the grass. I rebuilt everything Wed night and it looked mighty nice, well aside from the gnarly chain-suck damage from where it jumped the tracks back in February.

img_7844-1x7drive

Thurs and Fri commutes had their downs. I dropped the chain off the lowest gear in the back after I hit some bumps, and the clicks and pings were still there so I was seriously wondering if I hadn’t just blown $40 on a chainring I was never going to use again.

Friday night I gave it another look. Took some links out of the chain to give it a little more tension in the low gears and keep it from bouncing around. Next I readjusted the limit screws on the deraileur to help keep the chain on track. I also removed the left arm to tighten the bb cup which I noticed had a few threads exposed. While torquing the cup I found that the clicks happened even though neither the bearings nor the arms had any load on them which proved to me that there wasn’t any problem with those 2 components. It had to be something else in the frame. I looked everywhere for cracks or anything which could stress when it dawned on me…

Took the bike off the repair stand, removed the seatpost and tried wrenching on the bb again. Nothing. Cleaned the old grease off the seatpost and frame as best I could, wiped down the inside of the seat tube with park poly lube, and reinstalled the seatpost. Torqued again. Everything was silent. The pinging was from the seat tube rubbing against the seatpost all along. The kicker in troubleshooting it was that it would still make noise even if I was not in the saddle because it was the l/r stress of pedaling that caused the frame to flex some times and saddle movement others. Switching pedals would improve it in some cases because wider pedals would give more leverage than narrow ones.

After I got everything back together I took it for a ride around the block, put it in the highest gear and mashed on the pedals as hard as I could. Totally Quiet. I’m too nervous to claim victory over it since I’ve thought I had it beat 100 times before. For now I’m just going to enjoy having a bike with everything in working order. Chainline would probably be improved by a bottom bracket 1-1.5mm wider, but that is splitting hairs. Final damage on the wallet,

  1. Surly 94mm x 5 bolt 35t chainring = $40
  2. SRAM 12×32 7 speed cassette = $18
  3. KMC 7 speed chain = $6.50

Hope to recoup some of that by culling my chainring collection on Craigslist. Gearing is a little lower than before. Old setup was 11×28 with a 36t chainring. New is 12×32 with a 35. Noticable in a negative way on the high end, but worth it to give me the ability to haul loads up any hill. I don’t plan on taking it over 30mph anyway.

gain-ratio

If I was worried about speed I would have switched out the 2+ inch Kendas months ago. Surly Ring is pretty sweet. The tooth profile is much taller than my Blackspire Mono Veloce, Salsa, or stock ‘shifting’ rings. I imagine it will hold the chain and wear well.

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2 thoughts on “sprockets, torsion, and…

  1. Thanks. I respect my local LBS’s, but I’d rather spend what little bike money I get on bikes, instead of service.

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