When I was out on Sunday last:

http://www.bikeforums.net/showthread...=#post15827719

I was riding my bike down a slope and into a small stream ( to create a splash for a photo which involved riding down a stony slope and then off a small lip into a stream and then riding up a slope, turning round and coming back down.

I did that twice and then rode back up the small slope and got off my bike to hold a piece of fingerpost of the Pennine Bridleway for another pic.

When I got back on my bike I found I couldnt pedal it forward and it felt like the gears had slipped. I changed gear but it still wouldnt pedal so I jumped off and turned the bike upside down to find out what was wrong.

I found that the chain had come off the front chainring and jammed itself between it and the frame also becoming twisted in on itself.

I couldnt free it so had to finish the ride on foot and then take my bike to the LBS who have freed it up for me and I will pick it up tomorrow.

What could have caused that?

Have never known it to happen before, tho the chainring is worn and needs replacing the chain is new as are the rear chainring and jockey wheels.

Before those were replaced the chain used to jump off regularly but never jammed like that before.

Would appreciate any advice thanks.

Hopefully will be able to replace the chainring tomorrow.