Claris front mech drops the chain

[annirak]

I've had my road bike for three weeks now. The front mech worked well for the first two weeks, but this week, it has begun dropping the chain. I've now dropped my chain six times in the past three days. Each time I adjust the front mech, it seems okay until I ride it a bit, then it starts dropping the chain on the up-shift. It's as though the upper limit is drifting.

I've tried setting the limits a little tighter, but then I can't shift into the large chainring. Do I need to tweak the tension? Add some threadlocker? Get the limit set just right?

 

[cyberknight]

Is the chain dropping off the ring towards the frame or towards the pedal ?
If its the latter it could be that the mech is set a bit to high as it should only be the thickness of a 2 pence coin above the teeth of the large chain ring .
As the bike is only 3 weeks old did you buy it from a shop ? take it back as they should adjust it for free !

 

[annirak]

I bought it from CRC, so taking it back isn't really an option. It appears that the front mech is too high. There is roughly a 5mm gap between the tops of the teeth on the outer ring and the front derailleur.

I would go adjust it now, but that seems like a job for the weekend to me!

I found the dealer manual for the Claris groupset, and it's pretty clear about the installation requirements: 1-3mm clearance between the chain guide outer plate and the largest chainring.

It looks like I need to buy or borrow a torque wrench!

 

[DaveReading]

It's as though the upper limit is drifting.

Make a note of the orientation of the slot(s) on the H limit screw when you next set up the mech. Should the problem recur, you will be able to tell if it's moved..

Add some threadlocker?

If necessary, see above.

It looks like I need to buy or borrow a torque wrench!

You already have a torque wrench - your carefully calibrated arm! Using a normal 5mm Allen key, you shouldn't have any problem tightening the clamp bolt the right amount to stop the mech slipping. If you have one of those 3-way ones that give you more leverage, use your judgement to avoid overtightening it, though you're unlikely to snap the bolt or strip the thread.

 

[cyberknight]

You already have a torque wrench - your carefully calibrated arm! Using a normal 5mm Allen key, you shouldn't have any problem tightening the clamp bolt the right amount to stop the mech slipping. If you have one of those 3-way ones that give you more leverage, use your judgement to avoid overtightening it, though you're unlikely to snap the bolt or strip the thread.

+1
Make sure you keep the cgae aligned with the chain and you will need to adjust the cable as well when you drop the front mech down as well.Its not a big job but if your unsure take it to a LBS who could probably do it in 10 minutes tops !
Have a look at this

http://www.parktool.com/blog/repair-help/front-derailleur-adjustments

 

[annirak]

The saga continues. My front derailleur tensioner was so tight that I couldn't move it by hand. I used a pair of plumbing pliers and some cloth to remove the tensioner without marking it. Looking at the threads, it seems like the frame had the wrong thread for the tensioner and the mechanic just forced it in anyway.