Originally Posted by
3alarmer
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...the current crop of mechanics are all schooled in the Shimano Official Corporate Line, which states, "Thou shalt change the chain every 1.000 miles, and the cassette cogset every other chain swap." Which is a little bit on the anal side for most practical users who do not ride in severe conditions.
It's difficult to tell whether yoiu need to change out your cogs (or freewheel if your bike is that old and has one), without actually looking at it.
But by far your best course of action as a poor person who rides a bike is to buy yourself a KMC 6-8 speed chain (they are cheapest online, but you may be in a hurry), a tool to push out the pin to shorten the chain to the length you require 9match it to the old one), and then to see how well your bike works.
If you get a lot of skipping and jumping around, with poor shifting performance, you need to replace the cogs (or freewheel).
If you rode this chain long enough for it to break, there's a very good chance your cogs are worn too. Which is why the shop is telling you this and why it's that much to have them do it.
Dude, I'm one of the "current crop of mechanics" and nowhere in Shimano's technical training (either the dealer manual or in any of the S-tec videos) does Shimano recommend chain replacement on a mileage or time based interval. They recommend using a chain checker (and preferably theres--although their nicer one is actually a little more accurate than most), and replacing cogs and/or chainrings when the chain skips on them. If anything, most mechanics recommend replacement a little early because they use chain tools that slightly exaggerate chain wear, and because they also because we see how terrible people are to their bikes. If we see a chain that is 70% worn in, chances are the next time anyone checks it'll have completely blown out the cassette and chainrings on some bike for which parts are nearly impossible to find.
The shop is just giving you fair warning over the possibilities. Expect about $10-30 for the chain (depending on quality), maybe $25-40 for the freewheel, and if things are really bad you could be looking at $40-80 in chainrings, and potentially $10-50 in labor.
If you're interested in doing the work yourself, I'd recommend checking your current chain wear yourself to get an idea of how much needs replacing. The least expensive way is to take a ruler and measure 12 links. New, it should measure 12 inches, at 12 1/16 inches the conventional advice is to replace the chain, and everything else is still probably fine. At 12 1/8 inches you probably need to replace the cassette/freewheel, which requires the appropriate freewheel/locknut tool and a chain whip. If it's much more than that, or if the chainrings have a noticeable sharktooth pattern to their teeth, then you'll need to replace those as well. I'd also recommend checking to see if there are any bicycle cooperatives in your area if you want to learn to do the work yourself, as they'll have all the tools you need and will be able to provide you with help.