Chain off: bad shift or adjustment needed

jeepie

Hi there,

I shipped my chain over on the pedal side of the crank when moving from the small ring to the big ring on the commute this morning. The shifting felt a bit agricultural for the previous few shifts and then I lost the chain over the top. I put the chain back on and it's been perfect since.

My question is: could this just be down to a single bad shift (bad luck/poor changing timing) or should I be looking to adjust the front mech to make sure this never happens i.e. bring the front mech in slightly? Is the chain coming off once in a blue moon just part and parcel of cycling? Or should this never happen so I need to adjust the front mech slightly towards the crank on the outer limit screw.

Cheers for the advice.

J

getprg

Be useful to know what drivetrain/groupset you are using and what sort of use/maintenance it's had.

jeepie

It's SRAM Apex 34/50 with a long cage rear mech and 11-34 cassette. I've not touched it since I got it, other than cleaning and lubing. It's done 1,000 miles and been faultless.

(Confession time: I was trying the simultaneous front and rear change we've chatted about on here, but that's worked fine too for weeks)

Does that help?

getprg

Someone should be able to compare your experience with that set up. FWIW simultaneous front rear changes should be OK - as you have already discovered.

After 1000 miles some fine adjustments are usually necessary but over shifting usually should not be affected unless factory set up was a little bit out.

Usually tackle the problem in following order by carrying out following visual checks - see Park Tool website

If band on or braze on check tightness of cage mount bolts to see of they have loosened to allow cage alignment to change
Check outer chainring has not been bent.
Check front cage height versus big ring.
Check parallel front cage alignment with chain in big ring.
Check indexing.
If all ok then adjust limit screw (a little only remembering how many quarter or half turns so you can return to original settings!)

All my drivetrains are Shimano and this usually sorts out probs but my son's mtb is SRAM and I must admit I find that much more difficult to set up and get some chain off issues.