DnvrFox

Okay mechanics, I need your wise experience.

I have been using my Windsor Leeds road bike as a trainer for two winter seasons, plus using it as a "utility bike" during the rest of the year. About 2,000 outside miles on it. Unknown indoor trainer miles, but I use it regularly. It has been working fine with no problems. It is a Sora (8 speed cassette), triple, circa 2004.

Tuesday am I went to get on my trainer. As I worked through the chain rings and got on the small CR and was shifting back to the middle CR, it sucked chain something terrible. It really jammed in the space between the small chain ring and the middle chain ring, and then jammed in between the chain stay and the chain ring. It was quite difficult to get out.

Okay, I cleaned up everything, removing any gunk on the CR, the chain, the rear der wheels, etc. Chain was not "dry" in any way. I use a top quality lubricant.

Then I tried it again. Happened immediately. Once more a mess to get "unsucked."

Okay, I tried the middle and large and all was ok. But no luck with the small<>middle shift, kept jamming in there.

So, I took it to my friendly LBS mechanic. He checked it out and said it would have to go in the hospital for awhile while he figured out what was to him a somewhat perplexing problem. The small CR was not bent.

OK - he called last night. He has it fixed. He said there was too small a clearance between the small CR and the middle CR (he measured it with a device of some sort), and he put some spacers in and it is working fine. At my request, he also put a new chain in, as it was getting a bit worn (it doesn't take much for me to have a new chain installed). SO, I pick it up today.

I trust this LBS totally, and have done a lot of business with them, and they are excellent. However, when I asked the mechanic (who has worked on all my bikes) he could give no explanation as to why it worked fine Monday and not Tuesday!

To my knowledge, I did nothing unusual except to ride the trainer. He said there were no parts loose nor missing in the CR assembly.

Any thoughts?

NoRacer

Not a BM, but I'll take a stab at it and speculate that the frame was flexing more than it had in past trainer sessions causing the chain rings to be tilted while the rear wheel remains locked in place by the skewer lock. The chain would twist a little in conformance to the demands of the chain rings. You switch chain rings--the middle to small are at just the right amount of tilt/twist to cause the chain to get dropped into the wrong place.

Ok... who'll be the first to yell BS!

DnvrFox

Thanks for the thought.

FWIW, this happened at the beginning of the training session, and I was not yet giving any force to the pedals. Just sitting there peacably starting my pedaling.

NoRacer

Well, so much for that theory.

2manybikes

The small chain ring wears faster than the other chain rings because it is smaller and the pressure is not distributed over as large an area. The space between the teeth gets elongated eventually. The chain may not mesh into the teeth or shift out of the teeth because the rollers don't match perfectly. Sometimes it can cause the chain to not go onto the chain ring and slide off (over) the chain ring when shifting. Sometimes it will not release the chain as it should and carries the chain too long instead of it shifting off.
This is worse with a newer chain, as the wear is much different on the chain ring teeth and the chain.
Did you put a chain on sometime before it first started happening? If you have a new chain and you have a lot of wear on the old one did you get a new cassette too? This may or may not be a problem too, if you have a lot of wear on the chain and the cassette. This could happen if you ride in the rain and bad weather often and the chain gets pretty dirty in 2,000 miles. If your bike does not get dirty often I would not expect it to be that worn at this mileage.

I don't know of a way to really diagnose the problem except looking at the wear on the teeth and seeing the problem happen. The only way I know of to fix it is to replace the chain rings.

If it's working do nothing.

Again if you keep the drive train nice and clean I don't think it would wear that much in 2,000 miles. It depends on how dirty it gets in the winter etc. No way to know over the internet if this is it or something else. I brought this up as it is an easy one to miss.

wagathon

Not a BM either, but, sounds like you may have a big climb from the inner to the middle ring. Hopefully, your front dr is not set up ideally, i.e., just above the big ring, because that would be an easy fix. Otherwise, are we talking about a tooth difference of more that 10T between the two rings, and is this STI or friction shifting?

DnvrFox

I talked with the shop owner today as I picked up the bike.

His explanation was the same as offered by another poerson:

cyccommute 

Rather than an elogation of the teeth, I'd suspect a burr on the small chainring. As you shift up from the small chainring to the middle, the chain will scrape across the tops of the chainring teeth. The chainring teeth, assuming that it is aluminum, will bend and in some cases even tear out chunks of metal. The next time you shift to the small chainring, the burr will hold the chain and not release it smoothly. Sometimes it holds it way too long because the only tension on the chain is from the rear derailer. Since the rear derailer is in a fairly low tension state anyway, the chain just keeps traveling until it hits the chainstay. The chain will finally release but because you are in a high torque state, the chain is jammed rather forcefully into the gap between the chainstay and the middle or outer chainring.

If you change the inner chainwheel to a steel or titatium one, the problem will be lessened. Mountain bikers deal with this all the time. I doubt if you will find a mountain bike that is ridden off-road regularly that doesn't have a chewed up chainstay.

DnvrFox

Thanks. I will keep my eyes open. The LBS did remove the small CR and inspect it and they said it was fine. If it happens again, I will follow your recommendation.

cyccommute 

Sometimes the damage isn't that apparent, especially with a narrow chain like a 9 spd. A very small burr or tooth misalignment can be hard to miss.

As for the mess you made trying to get the chain out, since this seems to be an indoor bike (at least for now), clean the chain with mineral spirits so that it is nice and clean (a couple of rinsing will usually do) and put a good dry lube, like White Lightening or similar on it. The chain will be lubricated sufficently and it will be much cleaner. And you won't be flinging chain oil all over the house nor cursing as you use Lava to try and scrub all of the black icky stuff off your hands

DnvrFox

Well, it has a brand new chain just installed yesterday.

I currently use either tri-flow or white lightning or pedro's on my bikes.

It is an 8 speed chain.

cyccommute 

If you use White Lightning on your chain, cleaning the factory oil off of a new chain first will make it much cleaner.