Here the problem...

On my 24 speed MTB, the middle chainring slips when a lot of pressure is applied. I have looked at it, but it doesn't look any different than #1 and #2. Is it possible it is the chain itself and not the chainring. The bike/chain are about 7 years old. Can just one chainring be replaced?

7 years old? You may have some problems. I am going to assume (yeah, yeah, I know what they say) that you use your middle chainring more than the small and large, therefore it is worn more. You can replace the middle chainring by itself provided if it is not on a real low end bike where all 3 chainrings are attached as one unit. Here is where your problems may come in: chains stretch - quite a bit, especially after 7 years. Your chainrings and cogs (rear gears) have worn with the stretched chain. So, if you put a new chainring on and don't replace anything else, the middle chainring will not mesh properly with the old chain and guess what - it will skip also! Seems weird, but it happens. Usually when this happens it is necessary to replace all chainrings, cogs, and chain. Very expensive. Your least expensive bet may be to try and find a used chainring that has some life in it.

It is a little late for this advice, but it may help in the future: Replace your chain often. It will extend the life of your other more expensive drivetrain components. How often depends on how often you ride. I usually replace mine about 3x year on a MTB that probably sees 1800-2000 trail miles/year on it.

One other note, if you have to replace all of your drivetrain parts, it is usually cheaper to buy a whole new set of shimano cranks with the chainrings than to buy the individual chainrings.

Good luck.

Zackly what Riderx said.

My old shop manager friend claims replacing chains is like changing the motor oil - should do it frequently and it will save you CA$H.

7 years, nice time, i wished my chain/chainrings holds that long!

I will bet that your chainrings are just fine, unless the teeth have been worn down to pointy little hooks. (In which case, you have some nice circular saw blades there!)

No, you have a worn chain. You say that the bike and chain are seven years old, but you did not mention mileage. If the bike has only 3 or 4 000 miles, then the damage is not great...

First you'll need the check the chain for "stretch." Place a 12" ruler along the chain so that a pivot pin is neatly bisected by the 0" mark. Hold steady, and sight down to the 12" mark. It should neatly bisect another pivot pin. If the pivot pin is past the 12" mark by more than half the diameter of the pin, REPLACE the chain! Wait any longer, and the stretched chain will wreak havoc on the Shimano Hyperglide cassette's ramps and cut-outs. If you replace a really badly stretched chain... say, 1/8" or more, the ruined cassette will jump and skip so much as to render the bike unrideable.

NOTE: The metal of the chain does not actually stretch... friction and dirt wear the pivots, and elongate the pivot holes... microscopically. a few microns of wear, times 110 or more pivots, equalls 2, 3, 5 or more millimeters of elongation.

This was never much of a problem in the old friction shifter days... Once the chain began to drag the ground, it was time to replace it, no harm done. Now, though, it takes very little elongation to ruin a drivetrain.

Positive NOTE: Chainrings don't suffer much from chain stretch. They'll work fine, even worn down to little pointy hooks... until teeth begin to break off!

If the chain is as bad as I think it is, here is what you will need to do:

NOTE: This is not an expensive bike shop repair, if you lack the proper tools or experience. No dishonour. Take it to them. Watch and learn. Buy the wrench some lunch. They like burritos.

Otherwise, all you will need are:

Chain breaker, chain whip or a 2' length of old chain, and a Shimano lockring tool. This is perhaps $20 worth of tools.

Replace the cassette with one of the same configuration, for $25 to $40, then replace the chain with the best one you can afford, another $21 or so. Lube the chain, and ride.

Check the chain length each time you lubricate it, and replace it at 2 000 miles, even if it does not appear to be worn. Otherwise, you'll be replacing chains and cassettes every time.

Steele-Bike,
Just to re-emphasize what riderx said - At this point you should replace all parts:
1. Middle chain wheel if possible. If chain wheels are riveted, you will have to replace the crank.
2. The chain
3. The cassette or freewheel.

Assuming the parts are Shimano compatible you can get a new cassette for around $40. A freewheel is a little more. Chain wheels don't cost too much, but a crankset can run $70-200 or more. If you have an older standard square bottom bracket, you might even be able to get something less expensive. If it is Shimano splined BB, you are kind of locked in. Chain $20-30.

Let this be a lesson to you, Sonny. Replace that chain AT LEAST every 2000 miles even on a road bike. 500-1000 if you ride mtb on a lot of trail/dirt. And clean it every 100 or so or after every dirty ride. You can go a little long on a road bike, maybe 200 between cleanings.
Good luck,
Raymond

Sergio, I just can't picture you with dirty hands. Sure sounds like you've done this before, tho...

Thanks for all the input. The bike is a 1994 Specialized Hard Rock that I bought new, but then gave to a friend a couple years ago. He recently gave it back to me and this is when I noticed the chain slip. I would say the bike has ~10,000 miles on it.

I am on my way home now and will take a closer look at it. I think I had better also check the chain wear on the good MTB. No problems with that one yet, but I guess that's the point.

Maybe we should first understand what you mean by "chain-slip".

If you have not changed the chain or the sprockets, it is difficult to understand what would slip unless the teeth of the sprocket are worn to almost nothing.

Usually you don't notice the damage from stretched chain to sprocket "etching" until you put on a new chain and the sprocket teeth don't match it well.

What do you mean by chain slip? Do you mean you put it into gear and the chain keeps jumping off the sprocket teeth and lurching forward (usually with a violent and worry-some teeth grinding sound).?

The chain slips only when a lot of pressure is put on it. It works normally when cruising along, but when pedaling from a stop the chainring spins through the chain. It almost feels like there is not enough tension in the rear derailuer to hold the chain in place (that's just what it feels like, probably not what it is.) There is no visible wear, but I have yet to measure the chain for stretching.

Sounds like a rear derailleur problem to me, but I'm no expert.

It sounds like the shift levers and cable tension needs adjusting.

It is hard to guess without seeing it. If it is teeth wear and chain stretch, the damage is done together chain to teeth so that you don't usually notice the problem until you try to put on a new chain or sprocket. I suspect something else is going on.

Check shift lever and cable tension.

No chance that the front derailure is hitting the chain? Check that too.

Surely your wheel is centered correctly so the chain isn't trying to climb on the sprocket at an angle? Check that too.

Mike

This sounds similar to what happens when you get "chain suck" usually from a muddy chain. However, I suspect it is from a worn out chainring which can behave the same way under load.


I have to disagree with you on this one Cambronne, I have seen many chainrings ruined from stretched chains. Put on a new chain and the thing skips like mad. Replace the chainring and all is better. Also, I still ride friction shifters on my geared bike which this has happened on. This is the thing which taught me to replace my chain frequently. I still have a friend who doesn't follow this advice and as soon as he replaces the chain, all kinds of skipping occur on the middle ring. Seems like he'll never learn.

I was, of course, making a sweeping generalisation... But Mavic or Campagnolo ten-speeds seemed to be more resilient to neglected maintenance.

I spent my early days riding whatever used machines papa could obtain... Peugeot, Gitane, Raleigh, and one bright yellow mystery frame, with no label or decals... that, predictably, was the best bike I ever had. I don't recall ever changing a worn-out chain back then, perhaps because my bikes were usually stolen long before the parts wore out!

Also... and this is a documented "fact"... MILES cause more wear than KILOMETERS!

If I were to guess, I bet the older bikes had steel chainrings - any idea? Today's lightweight aluminum rings wear out quick and you will see"burrs" (for lack of a better word) on the edges of teeth which contribute to poor chain/chainring performance. I've never seen the burrs or kind of wear on steel granny gear chainrings I've had. Also, I think the bikes of yesteryear were built with longevity in mind more than the disposible parts we see today.

It figures. (need a smiley for "sigh"...)

Ooooh! I better switch to kilometers quick!

This is absolutely the case. Today's bikes are either built for lightweight or for reduced cost.

Both are achieved mostly through sacrifices to strength, durability, and longevity of the components.

Of course, bikes are lighter today than ever before, but clearly at the expense of reliability.

Regarding bikes and components, Keith Bontrager once said "Light, Cheap, Strong. Pick two."

This is one of the most accurate statements I have heard made.

I am glad to report that the problem has been fixed. First of all, I would like to thank all of you who told me that a chain needs replacing once it is "stretched". I had no idea that it ever needed replaced. The chain had stretched almost 1/2 inch. I assumed the chainring on the bike would be too worn to replace with a new chain, so I replaced the chain on the good bike and put that slightly stretched chain on the old bike. Both bikes now are good as new.

And to anybody who has not changed their chain recently, I highly recommend it. Now that I have put a new chain on the good bike, I cannot believe how smooth it now rides...no noise what so ever. I never thought riding to work could be so peaceful.

Glad to hear all is fixed.