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Old 08-27-12, 06:44 PM   #1
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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.
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Old 08-27-12, 06:47 PM   #2
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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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Old 08-27-12, 06:50 PM   #3
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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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Old 08-27-12, 07:12 PM   #4
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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!
You could do it your way, drill and countersink it on the inside, then tap it, and you can let the bare screw stick out toward the crank. The only problem I see with that approach is that after countersinking, there might not be enough thickness for a decent thread. Of course, you could countersink it to only a shallow depth, then file the head flush, since you won't be unscrewing it.
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Old 08-27-12, 07:33 PM   #5
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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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Old 08-27-12, 07:47 PM   #6
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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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Old 08-28-12, 02:52 PM   #7
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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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Old 08-28-12, 06:03 PM   #8
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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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Old 08-28-12, 06:10 PM   #9
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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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Old 08-28-12, 06:42 PM   #10
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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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Old 08-28-12, 07:00 PM   #11
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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.
That is interesting to know and makes sense. I know that if you look at the fit between the crank and ring on my Norman, you'd be hard put to place a piece of paper between them (well, that is not entirely true, but you get the idea) whereas on the newer cranks the gaps are noticeably larger.
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Old 08-28-12, 07:05 PM   #12
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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.
I'm really wanting the pin as a safety measure since the derailleur overshifted and the chain got stuck between the crank and chainring.
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Old 08-28-12, 07:10 PM   #13
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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.
I think the OP is referring to this type of pin:

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Old 08-28-12, 07:49 PM   #14
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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.
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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Old 08-28-12, 08:39 PM   #15
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Huh? you do understand that we're talking about the "anti-jam" pin between the arm and outer chainring, don't you?
Apparently not.
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