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Old 09-27-08, 02:31 PM   #1
Widsith
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Crank torque question

I have an SR Custom triple crankset (square spindle) and I haven't been able to find exact torque specifications for the cranks. Barnett's Manual says "In absence of manufacturer’s recommendations, torque to 350 inch-lbs" and I tried that. But afterward, it wouldn't shift to the smallest chainring any more. It [i]almost/i] shifted, but not quite. Apparently the chainrings are now slightly closer to the frame than they used to be. So I pulled the crank again and re-torqued it to 300 inch-lbs, plus adjusting the lower limit screw on the front derailleur a bit. Now it shifts correctly and the crank seems tight enough.

Did I do the right thing? Should I have left the crank torqued to 350 inch-lbs and just loosened the FD limit screw more? Also, the non-drive side crank is still torqued at 350 inch-lbs. Should I leave it alone or reduce it to match the drive-side crank?
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Old 09-27-08, 02:39 PM   #2
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Yes, you should have just tweaked the lower limit screw the first time. Removing and replacing square taper cranks repeatedly isn't a real good idea but can be done without harm if you torque them once per installation.

I'll bet the reduction from 350 to 300 inch-pounds isn't what solved your problem but the limit screw adjustment did.
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Old 09-27-08, 02:42 PM   #3
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Personal opinion would be to torque to spec and adjust the FD. The FD adjustments are easy; having a crank arm come loose would suck, to put it in simple terms.

I recently went through this with a square taper crank on my road bike. I had pulled the crank to try and find the source of a creaking noise (never did fix it) and retorqued to the middle of the manufacturers spec, as opposed to the lower end that I was using. I had to adjust my FD to be able to get into the little ring and to keep it from shifting off the big ring.
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Old 09-27-08, 02:50 PM   #4
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Yes, you should have just tweaked the lower limit screw the first time. Removing and replacing square taper cranks repeatedly isn't a real good idea but can be done without harm if you torque them once per installation.

I'll bet the reduction from 350 to 300 inch-pounds isn't what solved your problem but the limit screw adjustment did.
Actually, it was both; I adjusted the FD first and it worked OK while stationary, but on a test-ride it hesitated and didn't shift smoothly. After re-torquing the crank it shifted quickly and smoothly again.
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Old 09-27-08, 02:51 PM   #5
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Personal opinion would be to torque to spec and adjust the FD. The FD adjustments are easy; having a crank arm come loose would suck, to put it in simple terms.

I recently went through this with a square taper crank on my road bike. I had pulled the crank to try and find the source of a creaking noise (never did fix it) and retorqued to the middle of the manufacturers spec, as opposed to the lower end that I was using. I had to adjust my FD to be able to get into the little ring and to keep it from shifting off the big ring.
So should I go ahead and torque it a bit more, back up to 350 inch-pounds, and adjust the FD again if necessary?
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Old 09-27-08, 04:31 PM   #6
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YES! Definitely do NOT use crankarm-bolt torque as an "adjustment". Use other things that are adjustable to fine-tune the bike, like FD limit-screws and cable-tension. You just have to search "loose crankarm" on here to see how common the problem of loosening crankarms is. A buggered crankarm may not be that big a deal, but certainly is more frustrating than shifting problems, especially if it falls off miles away from home.
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Old 09-27-08, 05:15 PM   #7
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YES! Definitely do NOT use crankarm-bolt torque as an "adjustment". Use other things that are adjustable to fine-tune the bike, like FD limit-screws and cable-tension. You just have to search "loose crankarm" on here to see how common the problem of loosening crankarms is. A buggered crankarm may not be that big a deal, but certainly is more frustrating than shifting problems, especially if it falls off miles away from home.
OK, I'll put it back to 350 inch-lbs. That particular value seems rather arbitrary to me, since it wasn't a specific recommendation for my particular cranks, but a generic "if you can't get it elsewhere, use this" value. However, since I've already had it up to 350 once, I can see how it might get loose if I tried to use a lower torque now.
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Old 09-27-08, 05:24 PM   #8
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+1 Danno. You're doing the right thing. Torque it up.

We have several of us vintage bike & component knuckleheads here in B'ham if you ever want any help.
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Old 09-27-08, 05:33 PM   #9
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FWIW, Shimano recommends approximately the same torque value for it's square taper cranksets. I've used 360 in-lbs (30 ft-lbs) on all of the square taper cranks I've installed without issues.
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