Bent Cog

bent_cog_bromptonHere’s what almost ruined my morning on Monday. I decided to cycle the Brompton all the way into work, and went a different way as a change of scenery. At some point, my bike chain started making quite the racket, with a jarring action as I pedalled, but there was nothing visible wrong with the chain, and the gears seemed to be working just fine in terms of shifting – but the problem persists in all gears: The chain keeps trying to jump off the rear wheel every few inches, and then pops back on again. I could not see the problem at all, and I had to get into work for a meeting. My working theory was that I’d stretched the chain somehow so that it no longer fits the bike, but none of the tools I had were going to be able to help with that.

Happily, that different way I’d chosen meant that I could struggle on for a bit longer (enough to get me out of traffic, and do a bit of coasting when I could) and then walk the Brompton over from the end of Virgil to the subway stop at Wilshire and Vermont and complete my journey using the Red and Expo lines.

When I got it home, I put the bike on the high stand, and did a bit of investigation with the better visibility, and there it was. Bizarrely, the larger of the cogs is bent. I’ve no idea how I could have generated the torque and shear needed to do that, but apparently I did. You can just see the bending if you look closely in the picture (click for larger view). One if very bent, and the two neighbours are also off the alignment too…

I spoke with Craig at ElectricbikesLA (the closest local Brompton parts people, a little store I like to support) and I’ll be getting the cog (and perhaps the chain, since it took a beating) replaced today under warranty since it was just under a year ago that I replaced the entire rear wheel with a whole spanking new gear set (the lovely Sturmey-Archer evenly spaced internal gear hub, for those of you wondering, giving me a wider speed range too…)


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