Okay 50+rs, 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.

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.

So, I come to my wise friends in the 50+ forum to get their opinions as to what may have caused this seeming anomaly.

Any thoughts?

A couple of possibilities, both pure speculation:
Could one or both of the chainrings be worn, so there's a little "hook" shape in the teeth? Sometimes that can hang up the chain long enough to screw up the shift.
Or could the chain have been worn, alone or in combination with the rings? Seems unlikely, since you imply that you change chains often (puts you ahead of me--I almost never do). If the ring spacing (something I've never even thought about) was marginal to begin with, a fairly small glitch somewhere else might have jammed things up.
This is all guesswork, by the way. I've been riding more than 30 years and never had a case of chainsuck. I attribute it to my maintenance schedule, which requires that if something is still working, I rigorously ignore it.

I just picked up the bike and talked with the shop owner. He thinks this is the most likely explanation.

If the problem "appeared" suddenly, "something" happened. I've never seen the gap between rings get smaller with wear, it's usually the opposite. Too, I can't imagine that you could ride this thousands of miles and never have it happen and then all of a sudden have it happen twice in the space of a few minutes. However, it's very possible that respacing the rings will permanently solve the problem.

Personally, I'd look at the bottom bracket. When the bearings wear, the rings no longer are parallel to the chain line--they change angles or become "cocked". Combine the already too narrow gap between the rings to the rings running at a slight angle to the chainline and I'd think you have a recipe for some chain problems. Even though repairs have been made to the rings, I'd probably disassemble the bb, clean, lube and adjust--or if it's a sealed unit--replace it. I'd certainly inspect it at least.

Have fun!
John in Oregon

I had a set of rings on the Tandem which were steel Sugino. I wanted to change the small ring to a 24 from 26 and went to my LBS and bought a 24. The very experience you have hopefully just cured happened about every 3rd change, but from Middle to small. The problem had just occured when I changed the ring so it was quite obvious where the problem was. Like you it was spacing of the sprockets. My problem was- I now had to buy new sprockets for middle and large, so my cheap Cure works out a trifle expensive. I have since learnt not to even mix manufacturers rings on the same crankset.I wait until 2 rings are getting worn and buy a new crankset instead. Unless it is on the Tandem and then I always go for the same manufacturer in rings, but buy them in sets at a time. Tandem crank sets are a trifle expensive.

Why it has now caused a problem to you, is a mystery, unless it can be put down to wear taking place, and thus becoming apparent by the spacing that was not perfect in the first place. Only one thing for it-- You value your bike time too much so time to browse the 2006 catalogues.

Chainsuck is very difficult to diagnose, as there are so many different causes. Hopefully, the LBS was correct. In all likelihood, the problem didn't just suddenly appear. The chainring spacing may have been marginal in the first place, but still allowed things to work. But as the chainrings and chain wore and got more contaminated, it just finally reached the critical point where the combination of these factors was serious enough that the chainsuck actually happened. Once it got caught, the chain was probably slightly twisted, causing the problem to resurface, even though you cleaned the drivetrain. The symptoms are usually there before the problem occurs, but you don't always notice them.

It's like kicking a door open with your foot. You can kick it open repeatedly, without doing anything to your foot. But kicking a door open is the proper way to do it (ie marginal condition). Then next time - BANG! - you've got a sharp pain in your foot. You didn't do anything different, but the repeated stress in a marginal situation was causing wear and tear that you didn't notice until it reached the breaking point. It's the proverbial straw that broke the camel's back.

Hopefully, respacing the chainrings puts the set-up back to an optimum condition where the affects of slight wear and normal contamination will not cause a recurrance.

Make sure the rear wheel is properly mounted. If it slips forward or sideways a quarter inch, that can cause problems. Many "stock" chains are too long and have enough tension, especially when running on the middle ring and a middle cog. Taking a couple links out will increase chain tension.

Hey Denver.....

I take a totally different approach to the problem....

.....were you singing at the time?.......

Murray

I never even thought of that.

Of course . . . . . . . . . . . .

It would be interesting to put the chain ring back the way it was and see if just replacing the chain actually resolved the problem. But, I can understand that if it's now fine, why bother? I might do that just out of curosity... OHB

Another off the cuff (and probably profoundly wrong) idea: Has the "shifting ramp" pin fallen out of (or become worn in place) on the middle chain ring? Sometimes these pins are installed on middle chain rings to "kick" the chain up or down during shifting. If a pin falls out (I've seen this) or becomes worn to the point of being smooth-shouldered (I've seen this too), you might then have more clearance between rings. Keep in mind that the shifting ramp DOES extend outward from BOTH sides of the middle chain wheel. That clearance is taken into account by the manufacturer for between-ring clearances. The excess clearance created by the missing (or worn) shifting pin might just be enough to allow the chain to fall between rings when it reaches the tooth where it normally shifts.

This is pure speculation on my part. I've never experienced shifting problems like you describe even with middle rings that have ramp damage, but you never know...

Had a simular experiance, it was the freehub jammed & temp, turned it into a momentary fixed wheel !!