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Right, I need some help.
I keep dropping the chain off the small chain ring onto the bottom bracket shell when changing down from the middle ring.

Whats even more frustrating is that I put the chain back on the small chain ring, spin the cranks and the chain stays on it. I then start peddling and the chain drops off again.

Why is this happening? And what do I need to do to stop it?

Cheers in advance.

The lower stop on your front derailluer is too far on allowing the chain to jump too far, put the chain on the smaller ring and adjust the derailluer so it's 0.5mm off the chain.

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Ok, thanks

so I thought that might be the case. I have had this issue since before I removed the big ring and fitted a bash. I thought that I had adjusted the front correctly and had cured the problem but it seems not.

I have a 9 speed setup. When on the smallest chain ring how many of the rear cogs should I be able to use without the chain rubbing the front mech? the largest being 1 the smallest 9.

Following on from that when I am in what was the middle chain ring should I be able to use all 9 of the rear cogs with out rubbing the front mech?

You should be able to use all rear cassette gears with out the the chain rubbing on either side of the front mech if its set up correctly, the cage might be slightly bent/crushed or twisted on its mounting point on the frame

Shimano stuff sometimes rubs ever-so slightly on 9 but not enough to be an issue

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Techicicaly you should not run your gears over its full spread (e.g in granny and 9th out back or top and 1st out back if that makes sence) due to excess chain laterial force and wear but i would be lieing if i said i don't ride with my gears being like that time to time. Expect a little bit of rub on your front derailer but if your willing to spend a bit of time adjusting everything it should not happen.

Also have you got the correct spacers for your BB in place ? that 2mm plastic shim makes a lot of difference in alignment.

If it has just started to do it, when it didn't before, there is a good chance the mech has twisted around or the cage is bent. Recent crash? Otherwise, adjust the L limit screw to limit its travel as suggested above.

Cheers for the input, I havnt been able to get the bike in a stand and have another look at it yet.

Not had any crashes, and doesn't look bent. I cant remember if it first did it before or after I did what Evans told me to do to adjust gears when I didn't know any better. I don't use the granny that much but have been doing more hills recently so become much more of a problem.

Evans told me to use the barrel adjuster to set the gears up so I twiddled it a few times but that was 9 months ago, I now know its only to tension the cable. when I fitted the bash I only did the H screw.

When the builders have finished wrecking the garden and sorted out the man cave as the Mrs calls it, ill stick it in the stand and go through the gears from scratch.