Vintage TA Crankset Torque Spec?
 

Anybody know the crankarm fixing bolt torque spec for a vintage TA Cyclotourist crankset?

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.

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.

unless you are talking about the 5 small bolts that hold the outer chainring onto the crankarm.

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.

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

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.

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.

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.

Thank you Andy,
This message helped me tremendously. I realized that the aluminum cranks, like TA and Stronglight were softer and prone to bottoming out with too many off and on the spindle.
Cheers, hope you are still on the list.
Rita

That's roughly what I torqued my Nervar crank to on my Schwinn Super Sport 3-speed. IMO French cranks (T.A., Stronglight, Nervar) use a softer alloy than Japanese cranks- there is a distinct difference in feel when tightening them vs. Japanese cranks. I'd love to quantify the difference but I don't have the precision measuring equipment or spare vintage cranks to pursue this.

https://cimg7.ibsrv.net/gimg/bikefor...6ff53fc42c.jpg
i

You're welcome, but I didn't think it would be a 7 year old post (of mine) that would be so helpful:) Andy

We will all live on thanks to the Internet. I still refer to Sheldon Brown's pages even though he's been gone 12 years.

An old wives tale. Once the crank is torqued it should not be tightened again. Installing Cranks by Jobst Brandt (sheldonbrown.com)

davidad- Sorry but my years of LBS service work suggests otherwise. Although missing from your statement is that word "properly". As in properly tightened. The assumption of some other person before you doing a proper tightening is one that a good assembly mechanic can't make, if they want a stellar reputation. If they just want to get the bike out and are not on the receiving end of the problem when their assumption proves wrong then they will just repeat their poor assembly procedures. But if they do the pre sale check and do tighten (during the confirmation that the retaining bolt/nut is properly tightened) and they discover that the bolt/nut wasn't properly tightened by the "factory" then what do you say? That bolt was tightened twice, once enough to ship the bike with and the next to the proper torque range. So does that mean the bolt got 2 or 1 tightenings? Then there's the situations (usually during tune ups where every nut and bolt should be checked) when the mechanic finds that the crank bolts are far less tightened then the usual torque range. Does the mechanic leave the bolts as is, not as tight as most agree to being right? Or does the mechanic tighten the bolts to the right range? By your suggestion it would seem the right thing to do is to do nothing.

I have a problem with absolutes that are based on assumptions of other's work/procedures. Andy

I didn't say a thing about a new bike. If I said torqued then properly is assumed. This is for a crank that has been removed and installed. I am sorry, but I tend to follow Brandt because he is an engineer with exemplary credentials.

I often write for other then the OP. Those who take the time to post usually are at one end of the skill/experience range, or the other. As an engineer you should know the importance in saying what you mean. Those who don't have that experience or understandings and are trying to learn don't have the luxury of assuming much, if they want to learn good techniques.

I bring up new bikes because that's where/when most all cranks are last tightened, or at least for a very long time. I suggest that the vast number of cranks that fall off the axles are from lack of proper tightening diring the bike's out of box assembly or the presale check over. So in my world I see more value talking to this point then to those who service their own cranks after they have bought the bike from where/who ever. My suggestion that cranks should be retightened or checked for proper tightness is, IMO, a valid and good point. Independent on when this is done.

As to following Brandt- I agree that many of his thoughts are correct but do take issue with a few just the same. Andy

Much as I like Davidad's argument, mainly due to my innate laziness, I have had aluminum crank arms come loose and fall off after just one tightening with a torque wrench. I believe that you should go back over your crank arm bolts/nuts after a month or so of riding just to be sure they have stayed tight. Both arms that fell off stayed on after again tightening with a torque wrench and checking them in a month or so. All of the crank arms were used and had been on and off bikes before.