FD Cage Modification??
10-22-23, 09:21 AM
#26
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Regardless, Kontact suggestions, in my experience, are addressing the issue as described which is fairly common when using a low Q factor crank. I don't believe chainlne has anything at all to do with the problem as described. Sometimes I find I get my best shifting with the derailleur set such that, at its most extended position, there will be slight contact with the crank arm but one simply completes the shift and then immediately trims the derailleur back in very slightly. This is very easy with friction shifting and becomes automatic, but maybe not with indexed?
Since the OP has apparently checked out and is apparently not going to offer any further information or photos, there's not much more that can be said about this.
10-22-23, 11:46 AM
#27
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I had presumed he was going for indexed, but it's probably a mistake to presume anything in this forum.
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10-22-23, 11:50 AM
#28
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Chainline has everything to do with it, when you're talking about trying to use a FD designed for a 43.5mm chainline and trying to make it work on a bike with a 50mm chainline. He could try it, but shouldn't be surprised if it doesn't work.
Since the OP has apparently checked out and is apparently not going to offer any further information or photos, there's not much more that can be said about this.
Since the OP has apparently checked out and is apparently not going to offer any further information or photos, there's not much more that can be said about this.
But we are talking about a road crank. Road chainline is 43.5mm for a double and 45mm for a triple. If the difference between triple spacing for road and 73mm is 47.5 - 45 = 2.5, we can apply the same logic to the double and say that we need to add 2.5mm to the 43.5 chainline to give a double chainline of 46mm for 73mm. 46mm or even 47.5mm should not be that hard to get to with braze on adapter of the kind I pictured. And running the chainline slightly left is not going to cause an issue with 440mm chainstays.
The Ogre is not a tandem - I hypnotized myself with Tandem Tom's name. It is a top pull type MTB frame, so if the solution to the narrow road crank problem needs to be a slim road FD, then Tom will have to add a cable stop and pulley with the road FD.
That may all seem drastic, but that's what happens when you try to put parts based on 1970s road specs on modern MTB frames. If Tom doesn't like my suggestion, that's okay. Someone else can come up with a different solution than what I have for the small clearance this type of crank has between the outer chainring and crank arm. I went through the exact same thing when I decided to use a Sugino Mighty crankset on an 8 speed 130 spaced road bike. The 1990 Shimano derailleur I tried to use either rubbed the arm or the chain. Then I put a 1980 Superbe derailleur on it and the rub disappeared and the front shifting remained excellent.
Has anyone come up with a different solution? Doesn't seem like it.
Last edited by Kontact; 10-22-23 at 12:13 PM.
10-24-23, 05:47 AM
#29
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I've narrowed and widened FD cages before with some success. The one I widened was a Shimano FD that I ran in an otherwise all-SRAM drivetrain. The one I brought in had been bulged out by a dropped chain (and started rubbing the crank arm) so I flattened it out. I'm sure I violated all sorts of warranties, but they worked better after I had messed with them. I used pliers and I wish I had more precise tools but whatever. They were temporary fixes though and have both since been replaced.
10-24-23, 06:42 AM
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I've narrowed and widened FD cages before with some success. The one I widened was a Shimano FD that I ran in an otherwise all-SRAM drivetrain. The one I brought in had been bulged out by a dropped chain (and started rubbing the crank arm) so I flattened it out. I'm sure I violated all sorts of warranties, but they worked better after I had messed with them. I used pliers and I wish I had more precise tools but whatever. They were temporary fixes though and have both since been replaced.
