Chain Sneeze

Stone Glider

Got the Tourer back from the (not so) LBS on wednesday and went for a ride on thursday. Great, new chain and block (9 speed) very smooth enjoyed a gentle, fastish, for the loop. On sunday, lovely weather off for a longer spin including some hillier stuff. Reached the first ramp, part way up change to the little ring (it's a triple) at the steapest bit clang! clang! come to a stop, look down, chain wrapped round BB :shock:

No sign of damage, so I take the bike partway down to a flatter stretch and re- attach the chain. Check all is well with the drivetrain and pedal back up the hill Clang! same result :?

Push bike up rest of steep part, re-set chain but on middle ring and lowest gear, off I go. No problems, carry on the ride but on middle and large ring only. Reach home and have a think. Still no sign of defect, set the bike on little ring and pedal round estate roads up gentle slopes, no problems. Rode off to nearest, steepish hill and repeat process, when it got steepest two loud "sneezes" where chain seemed to miss then bit again and on I went, another "sneeze" shortly after then OK.

What's occurring folks? I would ask the n/sLBS but they are shut.

skyd0g

It sounds like the 'L' screw needs a slight adjustment (prob no more than half-a-turn or so) - looks like it's overshifting.
See guide here: http://www.parktool.com/repair/readhowto.asp?id=75

Wappygixer

You may have damaged a tooth on the small ring.They can be ok under normal loads but under pressure they can slip or jump the chain.
Also check the you dont have a bent tooth as this can do the same to.
Is the ring worn?Do the teeth look like shark fins?If so you'll need a new ring.
When you first changed gear to the small ring did you back of pedalling a bit?If you try to change gear under pressure it can destroy rings and chains etc.

Stone Glider

Thanks for the prompt replies folks. I have had a good look at the small ring but it looks no different to the others. All are worn but the n/s LBS was doing a service with authority to do as required. Th chain and the block were changed, the triple was judged fit for another year.

Everything is running smoothly ATM but not under any load. I shall try to get out Tuesday and try that hill again. I changed ring before the slope was steepest and without any heavy load on the drivetrain. I shall also twiddle (technical term) the adjustment screw.

Once again thanks for the advice

Chris.

kayakerchris

Hi I have had a very similar problem excpt that it is in my big chainring. I thought it was the chain, the cassette, etc before realising that it was the chainring. What i suggest is putting the bike in a stand and then turn the pedals whilst watching the chain ring. I found that at one particular tooth even under light load the chain "hesitated" before sitting on the tooth properly. looking at the tooth in question it was bent by ~0.5mm. However on a 10 speed chain under tension this was just enough to throw it off when pedalling really hard. I was able to bend the tooth back into place with a pair of pliers and it is now fine. However be aware that you can snap the tooth off very easily.

Good luck
Chris

Stone Glider

Took the bike to the n/sLBS this am. Mr Bike checked it over, se-set mechs to confirm alignment and took it for a ride. Big problem, trouble only occurs on hills, no hills to be had in locality, find longish ramp and try it. All OK, but Mr Bike not my size...... I try it, same problem returns (but milder). Change cassette to 8speed as on bike before service, all OK with Mr B... I try it, chain comes off! Back to 9speed cassette, more twiddling (technical term). Mr B tries OK......I try....Success!

So, many thanks Mr Bike, sorry I filled your morning (2+hours). Just hope the Sportive on Sunday is worth all your efforts.

Wappygixer

Stone Glider wrote:

Change cassette to 8speed as on bike before service, all OK with Mr B... I try it, chain comes off! Back to 9speed cassette, more twiddling (technical term). Mr B tries OK......I try....Success!

So you had an 8 speed cassette before and then changed it to a 9 speed?
What shifters are you using?

Stone Glider

Tiagra

PS: Mr Bike suggested that the inner ring should best be used with the two/three largest sprockets?? Beyond them the chain line was not optimal?? I didn't know that but there is a lot I don't know about bikes. That would not affect the problem I was having as the chain sneezed even when I had it inner ring and biggest sprocket.

mattward1979

this is indeed correct.

If you have a triple, you will have approx 10-12 useable gears with a 9 speed cassette (imo) as you want to keep the chain line as straight as possible.

on the biggest front chain ring, you will use the smallest and the 2-3 up from this on the rear cassette, and similarly with the smallest front chain ring you will use the biggest and the next 2-3 down from this.

the middle ring offers the most versatility in so much as it can use 4-5 of the rear chain rings.

Id say use this as a guideline and work out what feels right on your bike

Wappygixer

I cant understand why the bike shop would have fitted a 9 speed cassette if they had taken off an 8 speed?This seems very strange to me as STI's will only work with the cassette they were desinged for.An 9 speed isn't an 8 speed with an extra click added on the end, its a completely differnt spacing.
Yes chain line can make a difference but it still shouldn't drop the chain.I can climb all day on my big riing and on the largest rear sprocket without an issues (yes I know it can cause wear).
As a rule of thumb you shouldn't use the biggest and the biggest or the smallest on the smallest.
If your chainline is that bad maybe your bottom bracket is too long?

Stone Glider

Been out today on the hilliest hills near to me, not very but steep in parts. All is good. Thanks for the help.

Wgxr: the 9 sprocket block is to give me a 27 tooth bottom gear. A great idea, I climbed like I was in a lift today! I am not a Stone Glider by accident

amaferanga

Are you sure its a 9 speed cassette? It won't work very well with 8 speed shifters. And you can get a 27 tooth biggest sprocket on an 8 speed cassette.

woodywmb

We know why you would want 9spd over 8spd. What we would like to know is how it worked when the levers are limited to eight single cog movements? The chain wouldn't drop into your biggest ring at the back. Or possibly the smallest if the mech is reverse type. Did the bike shop switch shifters too?

Mike400

If I have read this right, your LBS fitted a 9 speed cassette to an 8 speed system, and has set it up as an 8 speed i.e. the 9th sprocket on the cassette is redundant?

Seems a bit of a bodge to me as you can get a decent enough range of 8 speed cassettes. I use a 7 speed on my commuter and even for that you can get a fair amount of choice re sprocket sizes.

Also as far as I was aware, an 8 speed cassette is the same width as a 9 speed, only with different spacing between the cogs and a narrower chain? if so the 9 speed cassette cant work that well with an 8 speed setup?

I think I would take it to another LBS and get a second opinion.....and im 90% certain they will want to change the cassette back to an 8 speed

on the other hand, if it aint broke......

Stone Glider

There is a story about some scientists who proved, theoretically, that bumble bees are too heavy to fly with the size wings they have. I feel a bit like the bumble bees. I don't know that it should not work but it does. I believe that Tiagra shifters are sold as able to handle a nine sprocket cassette, so no problem

amaferanga

Tiagra are 9 speed shifters so it seems unlikely that you actually had an 8 speed cassette and if you did then it wouldn't have worked well (it may have sort of worked, but it does seem bizarre that you ended up with 9 speed shifters and an 8 speed cassette - someone messed up there).

Stone Glider

Some feedback for all my correspondents. Completed a Sportive today, no problems

@ Mattward: I followed your guidance regarding choice of gears according to the front ring in action, many thanks.

Stone Glider

This is a bump to tell the tale in it's latest iteration. Riding to the pub on Wednesday only for the problems of the chain jumping start again The assembled company in the pub were unanimous, 'chain stretch/wear' so off to the (different) LBS I go. Collected it this am, new gear cables & chain, off I pedal. Ride to same hill where old trouble occurred and it repeats itself! Ho hum :x Get home with no more bother but avoiding little ring and steep ramps, ring (different) LBS. They agree to order a new inner ring, will call when in store. A little later (different) LBS ring back, 'we have had an idea, can we collect the bike?' Hour later, bike collected, two hours later, bike returned. 'We had an idea that the inner ring may be on backwards :shock: When we measured it against another triple it was, slightly, out. Took it off, turned it round works OK now'

Too late to put it to the test hill but what a fine effort from my new favourite LBS!

kayakerchris

The other thing that can give a similar type of hiccup under load is a chain that is too tight at one link. It runs fine most of the time but under load, the stiff link doesnt move smoothly onto the cassette. You can still put power down until the stiff link come over the top of the cassette when suddenly the bike seems to jump.

Stone Glider

Final Post: Have taken bike to various local hills on Sunday and today went to face my nemesis. All was good! Went up in my usual, slow but steady style, transmission was smooth and felt rock-solid.

So there you have it, obscure problem with jumping chain? Check the ring isn't inside-out! Well done my (different) LBS.