wrenching question: chainrings

[eddief]

110 bcd sugino double crank - 48/34 rings. I was switching out the Sugino 48 with an FSA 48. Sugino is pinned, FSA is ramped and pinned and prettier. What I noticed is that the Sugino has a long pin sticking out of it and when the ring was installed, that pin was right behind the crank arm. The pin is right in line with the chainring bolt that goes in behind the arm. What is this long pin for?

The FSA ring has one of these long pins sticking out of it too. But its pin is between bolt holes rather than right adjacent to the hole that goes behind the crank arm. So can't line up pin right behind the arm.

Do it make any difference where this long pin is in relation to crank arm or anything else? I would have thought that two 48 tooth 110 bcd chainrings would be exactly interchangeable with no questions.

[Kevan]

a chain wedgie! Ouch! :D

[eddief]

So Kevan, is the pin just to prevent the chain from wedging between arm and rings? Isn't it a bit weird it is not in the same place on two 5 bolt 110 bcd rings?

[dbrk]

In short, yes and yes. The pin is there to prevent the chain from dropping in there on a misshift or mishap and causing the crank to seize up (that being a very bad thing, as you would imagine). Where the pin goes is a matter for the manufacturer to decide but it would serve the same purpose.

yerpal,
dbrk

[dbrk]

In short, yes and yes. The pin is there to prevent the chain from dropping in there on a misshift or mishap and causing the crank to seize up (that being a very bad thing, as you would imagine). Where the pin goes is a matter for the manufacturer to decide but it would serve the same purpose.

yerpal,
dbrk

[Kevan]

the two cranks (Sugino/FSA) have different spider configurations, explaining the offset pin.

I think that's exactly your problem. So here's your next problem...

You don't have that safety pin located between the crank and the ring. This, as my "Ouch!" and dbrk's comments indicate, can be dangerous.

[JohnS]

My new Stronglight 48t chainring has two holes, depending on what brand crank you mount it on. You just screw the pin into the correct hole.

[eddief]

After looking at photos of FSA 110 cranks, they do indeed offset the bolt and the long pin to be NOT behind the crank arm. Sugino has the bolt and pin behind the crank arm. Risky business, I'll take a chance.