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Old 01-12-13, 05:25 AM   #1
Road Fan
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Vintage TA Crankset Torque Spec?

Anybody know the crankarm fixing bolt torque spec for a vintage TA Cyclotourist crankset?
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Old 01-12-13, 12:46 PM   #2
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I always tightened down the classic TA cranks pretty close to what all the other cotterless cranks got. About 25 ft lbs of torque. More inportantly is to recheck after a few initial hundred miles. Andy.
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Old 01-12-13, 12:51 PM   #3
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Lacking specific specs, a search on "metric bolt torque chart" or similar will yield some guidance. This is not an exotic aerospace application, those bolts are just standard hardware and should be fine when fastened as such.
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Old 01-12-13, 12:51 PM   #4
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unless you are talking about the 5 small bolts that hold the outer chainring onto the crankarm.
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Old 01-12-13, 12:54 PM   #5
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Quote:
Originally Posted by dsbrantjr View Post
Lacking specific specs, a search on "metric bolt torque chart" or similar will yield some guidance. This is not an exotic aerospace application, those bolts are just standard hardware and should be fine when fastened as such.
Except they're the fixing bolts for a square taper crankset, which means the torque values may be considerably higher than would normally be the case for that size of bolt.
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Old 01-12-13, 08:08 PM   #6
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Square taper crank fixing bolts (or nuts) are almost universally threaded M8x1.0 mm and the torque values specified for current Shimano and Campy cranks (25 - 30 lb-ft) should also be suitable for your TA
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Old 01-12-13, 09:12 PM   #7
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Yes, Park calls for 305 inch-lb for Shimano and a little more for Campy; same for Zinn's Art of Road Bike Maintenance. I feel that with a vintage TA that level of torque pulls the crankset rather far down on the spindle, more so than for a Campy system or a Shimano, both with the proper taper. I wonder if TA actually called for that much torque.

I also looked at a generic table of metric bolt torques, actually a few of them online. There is a range of values based on the grade of the bolt and with a lesser dependency on thread pitch. I don't know the grade of these bolts, but from lowest to highest, the torque specs vary from about 17 ft-lb to about 29 ft-lb (204 in-lb to 348 in-lb).

The only independent criteria I know is that with excessive torque the inner edge of the taper hole can be forced against the root of the taper where the spindle becomes round, and that if the spindle end is too close to the extractor seating face of the crank arm, the bolt will bottom on the spindle end and will not fully set the crank over the spindle taper. And that with insufficient torque the square taper hole can become distorted or the spindle flats will not bear on enough of the crank arm, eventually overstressing the crank arm.

I guess I need to try installing the crankset with around 305 in-lb, and see how it sits on the spindle ends. If it's pulled in too close to the frame in terms of spindle fit, frame clearance, or low chain line, I'll just have to get a longer BB. But it appears you guys believe that the full 305 is needed to stabilize the arm on teh spindle and prevent spindle hole distortion.
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Old 01-13-13, 06:26 AM   #8
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I just found something in Sutherland's 4th: Install the crank arm on a spindle with no oil or grease. For bolt-type, tighten to 18-20 ft-lb, with a re-torque at 100 miles or so. This recommendation is not at all brand-specific. I guess 18-20 is adequate if you keep an eye on it, but if the specific hard ware (say Campy or Shimano has a recommendation for a higher or lower torque, use that.

Sutherland's 6th says the same thing.
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Old 01-13-13, 09:41 AM   #9
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Road fan- This is pretty much what I already said. I always felt that the arms of TA cranks were a bit softer then the Campy/Sugino/Shimano of the same vintage so that's why I would set theit bolts just a touch less tight/on the low end of the common 25-30 ft lbs. And being old school i always recheck the bolts' tightness after a little riding. Andy.
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