Outer Chainring - No Pin Behind Crank Arm
Yesterday as I was riding my tandem, we threw the chain 2x as we were upshifting onto the large ring. One of the times it happened, the chain jammed between the chainring and the crank arm. I think the adjustment is properly set now, but would like to avoid the possibility of the chain getting jammed in the future. The outer chainring does not have a pin on it as some of the newer ones do. I was thinking that I could just drill and place a screw on the chainring behind the crank arm.
Is it OK to do what I'm thinking of doing or should I instead look for a chainring that has a pin instead? Thanks for your thoughts and input. |
Yes, go ahead and drill and tap the chainring. Then you can use a screw and small bushing. But it's important to file and protruding screw on he inside flush so the chain doesn't snag on it when on the inner ring.
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Got it. I was thinking that the screw head would need to be filed off on the inside of the chainring. Thanks!
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Originally Posted by photogravity
(Post 14660503)
Got it. I was thinking that the screw head would need to be filed off on the inside of the chainring. Thanks!
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Ah... I see what you're saying. You're saying to put the screw in from the outside and then cut and file the screw on the inside of the chainring. That actually makes more sense. I was just picturing it in reverse. Your idea is better and probably a lot cleaner looking.
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Yes, my first instinct was to go outside to inside with something like a pan head screw, and a short bushing or stack of washers under the head. If you can't find a decent bushing, I've used a short length of brake housing with the ends filed square, and whatever screw fits through after the liner is drilled or pushed out.
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No, drilling and tapping a hole in the chainring for a small bolt is perfectly fine. My Stronglight cranks from the 70s came from the factory with a pin done exactly that way.
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And my Sun Tour Cyclone crank, like the OP's, came with no pin on either the crank arm or the big chainring. It's the only crank I've ever owned that didn't have a chain catcher pin in at least one place.
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none of my pre mid-70s road cranks have pins, neither ST Superbe Pro, nor my Campys. I thing that the FDs of that era with flat outer plates allowed closer clearance between the chainrings and crank arms. As FD's started needing more clearance and chains got narrower the problem of the chain jamming inside of the right arm cropped up, and the pins were added.
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That pin is there to use as a guide to align the correct computer grinded angle flats on the chainrings. You may not need them on your tandem.
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Originally Posted by FBinNY
(Post 14665134)
none of my pre mid-70s road cranks have pins, neither ST Superbe Pro, nor my Campys. I thing that the FDs of that era with flat outer plates allowed closer clearance between the chainrings and crank arms. As FD's started needing more clearance and chains got narrower the problem of the chain jamming inside of the right arm cropped up, and the pins were added.
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Originally Posted by Lawrence08648
(Post 14665244)
That pin is there to use as a guide to align the correct computer grinded angle flats on the chainrings. You may not need them on your tandem.
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Originally Posted by Lawrence08648
(Post 14665244)
That pin is there to use as a guide to align the correct computer grinded angle flats on the chainrings. You may not need them on your tandem.
http://www.os2.dhs.org/~john/chainring-pin.jpg |
Originally Posted by Lawrence08648
(Post 14665244)
That pin is there to use as a guide to align the correct computer grinded angle flats on the chainrings. You may not need them on your tandem.
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Originally Posted by FBinNY
(Post 14665486)
Huh? you do understand that we're talking about the "anti-jam" pin between the arm and outer chainring, don't you?
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