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Chainring Rub(3 posts)

Chainring Rubcracker1973
Jul 29, 2002 1:31 PM
I recently upgraded part of my drivetrain from Ultegra to Dura-Ace, specifically the STI levers, derailleaur, and cassette. I changed cassette sizes from a 23-11 to a 25-12 and also changed my Ultegra chainrings from a 42a-53a to a 39b-53b. For some reason when I am in the small chainring, my chain rubs the big chainring when I'm shift up to gears 7,8, and 9. The chain does not rub the front-derailleaur at all. It rubs the inside of the big chainring. Any one ever heard of this or know what causes it?
re: Chainring RubChen2
Jul 29, 2002 1:53 PM
Sounds as if your chain-line is off. You should not have any chain rub against the big ring. Check to see that you don't have the inside ring reversed. The "39" stamping should face left, toward the frame. The "53" should face right, away from the frame. Or you may need a different bottom bracket or a spacer washer. Whatever it is it can be adjusted out.
Relatively commonKerry
Jul 29, 2002 4:42 PM
for the chain to rub on the big ring when on the smallest cog in back. Not so common for 3 cogs in back. Your center cog should be dead centered between the chain rings (use a long straight edge to confirm) to have the right chain line. If the rings are too far toward the BB (assuming they're installed properly on the crank set) then you should get a spacer to move the BB to the right. Do a search on this and you will find many threads.