Sprocket disintegration

April 13, 2020 at 17:01 | Posted in bicycles | 1 Comment
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I knew the drivetrain on my fixie was on its last legs. I had been moving the rear wheel back in the dropouts for a while, as the chain stretched. My drivetrain gets a rough deal. The last 200m of my ride to work is past a rock crushing plant, and there is grit and dirt all over the road. To keep the dust down, there is also a road sweeper spraying water everywhere continuously, which means that this last section basically sprays gritty mud up from the wheels all over the bike. And because I am lazy, I rarely clean my chain. Or my bike, actually. So the chain grinds away rather faster than it should.

Anyway, last time I had the bike serviced I had a complete new drivetrain – chainwheel, sprocket and chain. In the normal course of events, the cogs outlast the chain, so I thought i’d just buy a new chain and replace it myself. The new chain duly arrived, and I removed the old one (excitedly getting to use my chain breaker tool. I think it’s the second time I ave ever used it!).

I cleaned up the chainwheel and rear cog, but upon cleaning the rear cog found something a little disconcerting. It appeared that most of the teeth had sheared off. Apparently I was riding around with perhaps only 8 functional teeth out of 17…

My initial thought was to take it to the bike shop, but filled with enthusiasm after my chain-breaker tool experience, I broke out the chain whip and lock ring removal thingy (I don’t even know what it’s called). My tools are of the basic (read: cheap) variety, and often struggle with tight or tricky parts, but they actually did their job admirably, and I was able to get the lock ring and sprocket off with little difficulty.

I went looking for a replacement cog online; but it seems all the 17T ones were sold out. They had 16T and 18T aplenty, but no 17T – except for the cheap black ones that looked suspiciously like the one I had just taken off. My advice now would be to steer clear of such cogs made from pressed steel, and look for machined ones from hardened alloy. Oh well, I’ll keep looking. Or perhaps go into the bike shop just to get the sprocket…

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