Early on in the threads Wav produced about his Merc, he mentioned having an issue of misalignment with the chain tensioner. If I'm not mistaken, he said he had the ability to change it in some way. I interpreted that as an intension to 'realign' it. I'm just wondering if this is at the root of your chain woes 14R. When you look at the plastic tensioner they came with as standard, end on, loooking from the perspective the chain gets as it runs through, the jockeys look out of line with one another. They run in slightly different planes, one angled like a clock hour hand at '11 o' clock' and the other at '1 o' clock. I've seen a few of these and they were all like that as is the alluminium one. I don't know how exactly Wav's was 'out of line', but if he fixed this, he changed the design.

Did your chain come off at the sprocket or the chain ring 14R? If it was the sprocket, then maybe this is why. Mine has occasionally jumped off at the back, but only when bouncing over rough ground or potholes while pedaling hard. It's probably happened four times in 1700 miles..... then there were also the two bust tensioners, now hopefully cured by having a proper metal one.