chain jumping

jeffw0502

Firstly, ta to those that helped me out last time, issues sorted. Right, new problem, i've done about 700 miles on the bike since building it and recently, every 4 or 5 turns of the pedals, the chain will jump. It started doing it with the last cassette and since, I have fitted an 11-28 cassette to give a bit extra for the hills. I thought it may have cured it but it hasn't. So I've looked at the alignment and looks okay, doesn't make a noise and not trying too change up or down on its own or owt like that. Next I looked at the chain length and consulted the Zinn bible, and was way out, took ahem, 4 links out and on the stand its running a treat, get my arse on it and put a bit of strain on it and it's no better, I'm now thinking a new chain but its only done 700 miles or so, can't have worn already, can it ? On top of this, done about 20 miles on it last week with the new cassette and didn't jump till I was about 3 miles from home, and its intermittent as well

sungod

if everything looks ok, measure the chain to see if it's worn...

http://sheldonbrown.com/chains.html

scroll almost to the end of the page, look for "Measuring Chain Wear"

if it's ok, go through the adjustment procedure for the rear mech

onbike 1939

This could be a stiff link but again it depends how it's jumping. If the chain is hopping down a cog then it could be a lack of tension on the cable causing this.

markos1963

Have you checked the outer cable length or it's condition? If cut wrongly it can effect the gear change stopping the deraillier from moving the correct amount. A dirty or frayed cable can have the same effect.

jeffw0502

It shifts really well, but jumps round a tooth and stays on the same cog, on the stand it is OK, doesn't jump, only when ridden, although I reckon if I turn it with the brake on on the stand it might jump, not tried that yet. I came mind what chain it is, might be a Clark's (halfords special). If it was a stiff link, would it not do it all the time ?

onbike 1939

jeffw0502 wrote:

It shifts really well, but jumps round a tooth and stays on the same cog, on the stand it is OK, doesn't jump, only when ridden, although I reckon if I turn it with the brake on on the stand it might jump, not tried that yet. I came mind what chain it is, might be a Clark's (halfords special). If it was a stiff link, would it not do it all the time ?

If it is a stiff link it can be usually spotted by watching the chain as it runs backwards. It jumps as it runs over the sprocket.

laurentian

I can't believe I'm actually offering advice on here but, after suffering a similar problem following cassette and chain change, you may want to read this thread: viewtopic.php?f=40004&t=12917817

I had, what sounds to be a very similar problem and, with the help of Keef, managed to sort it.

All changes were great on the stand but when riding, the jump occurred. I found the "bad link" by looking head on (ie towards the cassette) from the crank on the "inside" of the chain.

I hope that is of some use or at least takes it out of the equation.

jeffw0502

Indeed it was, just took it off, cleaned it and one link was as tight as a nuns. Again people thanks for the help. If anyone is doing the Wiggle Jurassic Beast next month, see you there.