Hi, I wonder if some of the resident experts could give me a little advice on some drivetrain issues I am having.
I recently bought a lovely set of Middleburn RS3s from a gentleman off this site, and am having some problems with ideal BB sizing and front mech compatibility. The bike is a 1996/7 Orange P7 that can be seen in the readers gallery. It originally came with an STX RC groupset, including a delightful e-type front mech and BB. In a typically spendthrift fashion I believed I could just put 2.5mm of spacers onto the UN52E BB to replace the mech mount, but it appears the axle is offset inside the housing (aligned on a 68mm shell), thus the crank spider began to touch the BB shell as I tightened the crank on. I didn't tighten any further, just took them off; Middleburn recommend 113mm axle for the RS7/8, can anyone confirm that a 68*113mm BB will fit these correctly and get the chainline on target? Which brings me onto the front mech woes...
I was intending to use the Middleburns with my old XT M739 top pull bottom swing mech that I had on my Clockwork, but when that turned out to be a 28.6mm band I swapped it for a 31.8 top pull top swing M739. This seems to be alright, apart from the fact that the seat tube is slightly ovalised at the BB shell. This is not very pronounced (for instance, my old Clockwork was much more ovalised), but it seems an attempt must be made to remedy it. I have the cage down to 3-4mm above the big chainring, and it fits the tube fine but I think to get to 2mm or below I may damage the nickel finish or worse. Someone has suggested shimming the band with a piece of drinks can; is this effective? Would i be better shaving a little of the inside of the band (i reckon 0.3 mm on left and right sides)? Or alternatively just replace the 44T big ring with a 46T? Or just try and find a bottom swing front mech somewhere!
Sorry about all the questions, but I spent 3 hours after work today only to render my bike inoperative. Cannot believe I am going to have to get the bus to work tomorrow!
Best wishes,
James.
I recently bought a lovely set of Middleburn RS3s from a gentleman off this site, and am having some problems with ideal BB sizing and front mech compatibility. The bike is a 1996/7 Orange P7 that can be seen in the readers gallery. It originally came with an STX RC groupset, including a delightful e-type front mech and BB. In a typically spendthrift fashion I believed I could just put 2.5mm of spacers onto the UN52E BB to replace the mech mount, but it appears the axle is offset inside the housing (aligned on a 68mm shell), thus the crank spider began to touch the BB shell as I tightened the crank on. I didn't tighten any further, just took them off; Middleburn recommend 113mm axle for the RS7/8, can anyone confirm that a 68*113mm BB will fit these correctly and get the chainline on target? Which brings me onto the front mech woes...
I was intending to use the Middleburns with my old XT M739 top pull bottom swing mech that I had on my Clockwork, but when that turned out to be a 28.6mm band I swapped it for a 31.8 top pull top swing M739. This seems to be alright, apart from the fact that the seat tube is slightly ovalised at the BB shell. This is not very pronounced (for instance, my old Clockwork was much more ovalised), but it seems an attempt must be made to remedy it. I have the cage down to 3-4mm above the big chainring, and it fits the tube fine but I think to get to 2mm or below I may damage the nickel finish or worse. Someone has suggested shimming the band with a piece of drinks can; is this effective? Would i be better shaving a little of the inside of the band (i reckon 0.3 mm on left and right sides)? Or alternatively just replace the 44T big ring with a 46T? Or just try and find a bottom swing front mech somewhere!
Sorry about all the questions, but I spent 3 hours after work today only to render my bike inoperative. Cannot believe I am going to have to get the bus to work tomorrow!
Best wishes,
James.
