Bicycle Mechanics - Skipping Chain - I'm kind of a newb.
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05-15-08, 06:44 PM
I have a Kona Fire Mountain mountain bike. I use it for commuting. Roughly 10,000 km on it.
3 rings in the front, 8 gears in the rear. The gears in the back are newish. The middle ring in the front is newer. The small and big rings are original.
Entry level shimano derailleurs. Front is original, I replaced the rear 2 years ago when it broke in half.
Brand new chain.
When the chain is on any of the small (outer) rear gears and I pedal the chain skips over the rear like crazy. If I pedal slowly with no force it operates okay, but as soon as I apply a force required to accelerate, the chain skips over the rear gears. The teeth look okay. The problem only began when I replaced the old chain with the new chain (same chain, shimano HG50, 6-7-8 speed). I used the same number of links etc.
I have been tuning my own using resources like sheldon brown and parktool with success for over 2 years, but I'm by no means proficient in bicycle maintenance. I do believe my cable slack, and hi-low settings and everything are fine. I tune my bike by flipping it upside down and putting it on the ground with the seat and handlebar ends acting as a tri-pod.
Can the springs in the rear derailleur be weak and allowing slack when the chain's on the small gears to skip?
Do you have any other ideas I can try?
Do you suggest simply taking it to a bike shop?
I hate to say it but this sounds as if the old chain was on the bike too long, was stretched and disfigured the cassette cogs. If that is the case you'll need a new cassette and 8-speeds are getting harder to find. Did you measure the old chain for stretch?
05-15-08, 09:50 PM
This may be just a case of neglecting my bike too much. During the winter, I tend to just ride it until spring with no maintenance. I hate working in the cold.
I did not measure the old chain, but I still have it. Do I need a chain measuring tool to do it? I haven't got one. Last time I brought a chain in to a shop, they said it's stretched beyond the range of their tool, and i've treated the most recent chain very similarily.
It sounds very possible I damaged my cogs over a long winter of abuse.
The little wheels in my derailleur seems to have significant lateral wiggle, for what it's worth I think I'll swap it out too.
05-15-08, 10:19 PM
I wouldn't take it to a shop unless I KNEW that they were competent. I've heard way too many horror stories and butcher jobs - some that I had to fix.
Chain skip is one of the more common complaints. Unfortunately, it can be caused by ALOT of malfunctions. Could be worn cogs, misalignment of rear derailler, bent drop out, weak derailler cage spring(s). Is the chain physically slipping around the cogs, or does it just feel like it? Could be the ratchets in your cassette are worn and slipping. You know, two of the above problems would be dealt with in one swoop by replacing the cassette. They aren't too expensive - try Bike Nashbar.
05-15-08, 10:46 PM
One thing I didn't see - is this thing shifting gears when it slips or is it just sliding over the teeth? Could help make a diagnosis.
05-16-08, 07:46 AM
This sure sounds like a worn cassette... A "stretched" chain will reshape your most commonly used cassette cogs in very little distance. 1,000 mi (1,600 or so km) is sometimes all that it'll take. When you finally install a new chain, it's too late.
1) Figure out how many km you can get out of a chain before it's time to replace it... That'll be trial & error, unless you want to get a chain tool or measure links with a ruler. Let's say that you eventually figure out that you can go 5,oookm on a chain. Make yourself a note (I put a small P-Touch label on the drive-side chainstay)
and swap out the chain at that kilometrage, no matter what the chain tool says.
Doing this might cause you to swap a chain before you've eked 100% of its life from it, but you'll save the rest of your drivetrain. Besides, if you pull a chain that isn't completely worn out, you can always reinstall it or keep it for your beater/rain bike. No reason you can't run the same cassette & chainrings for 50,000km or more.
2) Run the chain until it's almost ready to chew up the chainrings, and swap it and the cassette at the same time. I have a friend who owns a bike shop, and this is what he does. When you get your parts wholesale, I suppose you can afford to run them into the ground. Of course, he also uses 30W motor oil as chain lube, so he's a cheapskate from go.
This helps me: When I pull a worn chain, I lay it out on newspapers, then I unpackage the new chain and lay it out alongside the old one. It becomes obvious how much the old chain has "stretched." Rough rule, if the old chain is 1/4 link longer than the new one, the cassette is probably damaged. I'll usually take a test ride up the steep hill past my house. If I detect any skipping, in I go to spin on a new cassette.
Plus, while the two chains are side by side, it's easy to mark the new one to length with a Sharpie so I can remove the extra links. That relieves me from having to count the links and hope the new chain is cut to the right length.
I did not measure the old chain, but I still have it. Do I need a chain measuring tool to do it?
A chain measuring tool would help but what is best is a good steel ruler. A new chain will measure exactly 12 inches over a 24 pin interval. You should replace a chain by the time that interval has stretched to 12 1/16 inches. If you stick to this rule a good cassette will last at least 3 times as long as a chain.
05-28-08, 05:59 PM
Thanks for the help.
I replaced the cassette and the skipping is gone!
I measured 24 pins of the old chain, it was a pubic hair over 12 1/8 inches. Looks like I over did it.
I maintain my bike well in the summer, but in the winter, I just set it and forget it, then deal with the replacements in the spring. $65 in bike parts per year is roughly what a cager pays to fill 1 tank in his car here in Canada, so I'm still way ahead of the game.
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