I've just built a 14" 456 up for my girlfriend using brand new quality kit. I used the same transmission set up as I run successfuly on my own 18" 456.... Middleburn Square taper cranks, 68/113 bottom bracket, Middleburn Hardcoat Slickshift Chain rings and XT kit with a £40 KMC chain. On her first ride out she started getting chainsuck when changing down and the chain travelled round middle ring and up round the chain stay, scratching the new frame. I rode it and got the same thing. We took it back to the workstand but everything was set up properly so I swapped out the Middleburn chainrings for a brand new set of Blackspire rings. The result was perfect, trouble free changing with no hint of the problem recurring.
I've used Middleburn Chainrings for ages and never had this problem and visualy I'm struggling to identify any obvious fault with these. I can't think of any other explanation except that there is something wrong with these Chainrings. Thus I've sent them back to Middleburn with a covering note and I'm waiting on their reply.
Has anybody any other ideas as to what went wrong?