Okay, chow down on that bean-and-cheese burrito and head out to the garage. We know you put in a long day, so let’s keep this one simple. We are going to run through your bike’s drivetrain.
1. Spin it: Clamp your bike to a bike stand, hook it to a low-hanging branch or flip it upside down. (A last resort, because it is difficult to shift the bike in this position, if you have air in your hydraulic brakes the bubbles might go where they will diminish braking performance, and finally, you’re going to scrape your grips or shifters and saddle.) You want to be able to spin the cranks and have the chain and rear wheel rotate easily. We are also assuming that you followed our advice about adjusting your derailleurs (“Garage Files” February, 2008) and the bike was shifting properly on your last ride. Clean up the chain, chainrings and cassette using a toilet brush (gets in the nooks and crannies better than anything actually made for the job).
2. Eyeball truing: Imagine looking down the drivetrain like you would look down the iron sights of a shotgun. The rear sight is where the chain leaves the cassette and the front sight is where the chainring picks up the chain. Run the bike through all its gears while sighting down the drivetrain in this manner. You are watching for wobbles or chain jumping.
3. Rear clear: If the chain is doing a little dance off the cassette, don’t rush out and buy a new cassette (or pack of cogs). First, take a thin screwdriver and clean out anything that might be packed in between the cogs. Nine-speed cassettes are notorious for being thrown off track by fairly small amounts of dirt or foliage.
4. All work, no play: It is unlikely that your cogs are loose, because you would have heard a jangling sound while riding. If they are loose, you need to snug the cassette lockring with a lockring tool. Pull the wheel off. Slip the lockring tool into the lockring and snug it up.
5. Easy fix: If there is a wobble where the chain contacts the chainring, check the mounting hardware to make sure it is all tight. If everything is tight and it still wobbles, there is a good chance that the rock you pegged (or riding with the hardware loose) bent the chainring (90 percent of the time it will be your big ring). We’ve seen riders true a chainring using a rock, but this was to get out of the woods. If it is bent enough that you see it wobble or that it rubs on a perfectly adjusted derailleur, the chainring needs to be replaced.
6. Chain wear: Measure a one-foot length of your chain, placing an inch mark of the tape measure in the middle of one rivet. Look at the corresponding rivet 12 links away. On a new chain, this rivet will line up exactly with the six-inch mark.
7. Replace time: With a worn chain, the rivet will be past the inch mark. If the rivet is less than 1/16-inch past the mark, all is well. If the rivet is 1/16-inch past the mark, you should replace the chain (and you probably don’t have to worry about replacing even the most commonly used cogs).
8. Repair it: If the rivet is 1/8-inch past the mark, you pushed the chain past its life span and some of the cogs (the favorite ones) will be badly worn. If you replace a chain that has gone past the 1/8-inch mark, without replacing the sprockets, it may shift fine and not skip under power, but the worn sprockets will cause your new chain to wear faster than it should. Use your best judgment.
9. Final drivetrain tip: If you do replace any component, don’t immediately head out for a long ride. Do a short test ride, including a significant hill, to make sure that the new parts are compatible with the old parts. You’ll know if there is a problem if the chain skips under maximum efforts.
The Garage Files is a monthly feature of Mountain Bike Action. The following links will take you to more Garage Files.
Spending Time Behind Bars, Click Here.
Curing Brake Noise And Rub, Click Here.
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