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Old 02-12-12, 04:08 PM   #1
r0ckh0und 
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Suntour AR FD

Suntour AR FD Range

I asked about this over in C&V but did'nt get any response, so....

I'm finishing up an overhaul on my Sekai 2500 Grandtour and am having an issue engaging the big ring with the FD. Bike appears to be stock with an add on triple and the Suntour AR is designed for a double. It will engage when the chain is on the outer half of the freewheel but it does'nt seem to be to happy about transfering over.

I'm thinking a shorter BB spindle might solve the problem as it looks like there is plenty of clearance between the small ring and the chain stay (about 6mm). Otherwise, what would be a suitable replacement, something that matches up well aesthetically with the Suntour ARX RD? Or, any other suggestions are welcome.
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Old 02-12-12, 04:18 PM   #2
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5 - 6 mm clearance is normal between the chainrings and the chainstay . you wouldn't want it closer then the derailer may not drop the chain onto the smallest . there are limits in the derailer both ways. and it normal to use the first three cogs on the rear with the big one in the front ,that way you don't get crosscogging . same go for middle to middles and the smallest with the low gears . try adjusting the high (h) strew on the derailer and see if that help .
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Old 02-12-12, 04:23 PM   #3
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Yes, I have the limit screw maxed out.
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Old 02-12-12, 04:35 PM   #4
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IF you have an adjustable cup type BB, you MIGHT find swapping the spindle will change the CL.
Some spindles are symmetrical & some aren't. OTOH, you might already have the "short end" on the drive side?
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Old 02-12-12, 04:45 PM   #5
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I'm usually pretty careful with that and I did double check. Non symmetric and the long end is on the drive side. I could try flipping and see what the difference would be. I think 2mm less would be plenty and still leave me enough range on the granny side.
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Old 02-12-12, 05:01 PM   #6
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flipping the axle might work ,only way to tell is to try .
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Old 02-12-12, 05:53 PM   #7
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Otherwise, what would be a suitable replacement, something that matches up well aesthetically with the Suntour ARX RD? Or, any other suggestions are welcome.
Suntour Mountech, perhaps.
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Old 02-12-12, 07:49 PM   #8
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My '85 Bridgestone 400 came with a Sun Tour ARX fd and it handled a triple SR crank with no problems and the SR bb spindle was installed with the long end toward the drive side. If, as you said, the high limit screw is backed out all the way, I expect a reversed or shorter bb spindle is the only way to go.
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Old 02-12-12, 08:22 PM   #9
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5 - 6 mm clearance is normal between the chainrings and the chainstay . you wouldn't want it closer then the derailer may not drop the chain onto the smallest
Rather than guess at your chainline based on chainstay clearance (irrelevant) why not just measure? According to Sheldon's chainline article http://sheldonbrown.com/chainline.html for a road triple you want a chainline of 45mm.

Once that is confirmed then see how it shifts. What size rings are you using? If your largest is a 48-50 you might be able to use an 80s MTB FD if you're looking for something cheap/available which might work better than the double FD you have now.
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Old 02-12-12, 09:11 PM   #10
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Chainline is 45mm like it should be.................52-47-34 rings.

Rear chainline is 42/43mm
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Old 02-13-12, 01:26 PM   #11
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I flipped the spindle this morning and it pushed the small ring against the chainstay. So I re-installed the original way.

When I had originaly mounted the crankset back on it felt a bit wobbly on the square tapered spindle and when I removed it, it came off pretty easily, this time it felt snug prior to tightening. I did'nt think it would make that big of a difference but it does shift up to the large ring much better now. So, perhaps I did not have it tight enough or it needed to be in the same position on the taper as when it was first installed.

Thanks for the help all.
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Old 02-13-12, 06:19 PM   #12
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Quote:
Originally Posted by r0ckh0und View Post
I flipped the spindle this morning and it pushed the small ring against the chainstay. So I re-installed the original way.

When I had originaly mounted the crankset back on it felt a bit wobbly on the square tapered spindle and when I removed it, it came off pretty easily, this time it felt snug prior to tightening. I did'nt think it would make that big of a difference but it does shift up to the large ring much better now. So, perhaps I did not have it tight enough or it needed to be in the same position on the taper as when it was first installed.

Thanks for the help all.
You got lucky. A crank arm installed on a square taper spindle and not torqued sufficiently WILL get loose while riding and WILL be ruined by having the square hole wallowed out by the spindle. Once the hole is distorted there is no saving it. Square taper crank arms have installation torque specs of 300 - 400 inch-pounds for a reason and that is much tighter than you would think.
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