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Crank Bolt Torque

Old 07-26-11, 06:26 PM
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yummygooey
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Crank Bolt Torque

Is there any way to "feel" what the right torque might be for a square taper crankset? I don't have a torque wrench. Or is "tight" good enough? I have a short little 6" ratcheting wrench that I used.

The article on SB's site says that you should not retighten the crank bolts if they loosen over time... so what do I do if I find that my crank bolts have loosened?
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Old 07-26-11, 07:02 PM
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If you torque the crank bolts properly when you first install them, it should not be necessary to retorque them until you remove the crank arms for service. They should never loosen enough to allow the crank arms to get loose on the spindle and, if they do, the arms are probably ruined.

As to "how tight", probably a lot tighter than you thing or can apply with a short ratchet. The recommended torque is 300-400 inch-pounds which is very tight. I get them as tight as I comfortably can with a 3/8" square drive ratchet and then the torque wrench often tightens them a half turn or more to get to spec.
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Old 07-26-11, 07:05 PM
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If you're used to turning bolts and have good hand feel, you can get by without a cone wrench. As the crank comes up to position the needed torque will rise steadily. Near final tight the torque will ramp up much faster, as of coming to the wall. After that it's maybe another quarter turn up into the wall (so to speak) and it's quits.

A 6" wrench may not be enough, but an 8-10" is plenty. As I said decent hand feel is needed, but anyone whose tightened stuff long enough can do this.
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Old 07-26-11, 07:22 PM
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using a 6" wrench 300-400 inch-pounds would be 50->66 pounds of pressure. If you have a 12" wrench it'll be ~25-33 pounds of pressure - etc...

If you have a sense of how much pressure that much weight is you'll get it close enough.

Before I had a torque wrench and i was worried about torque - and i'm a little embarrassed by this but it works great - i got my bathroom scale out and pushed as hard as it took to register the amount of weight i needed to apply given my wrench length. Once you have a decent sense of that amount of force you can probably get to within 10% of it pretty easily on the wrench. YMMV of course
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Old 07-26-11, 07:25 PM
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Thanks for the input everyone. Ya'll are always super helpful!

Assuming I'm way under torque (since I only have a 6" ratchet), if my bolts were to come loose a little I can just tighten them back up since I haven't hit that torque spec, right? No need to take the arm off and reinstall, and no need to worry about splitting the spindle hole?

I'll go find a torque wrench and get these bolts tightened to spec ASAP. At this point, I think I do enough of my own wrenching to justify a decent tool set. I'm just trying to gauge how much damage (if any) was done. I've probably only put like 10 miles on these crank arms so I don't think I did anything catastrophic.

Also, what are your views on greasing a spindle/not greasing a spindle? I've always been told to not grease a square taper, but Sheldon's site suggests otherwise.
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Old 07-26-11, 08:17 PM
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Originally Posted by yummygooey View Post
Thanks for the input everyone. Ya'll are always super helpful!

Assuming I'm way under torque (since I only have a 6" ratchet), if my bolts were to come loose a little I can just tighten them back up since I haven't hit that torque spec, right? No need to take the arm off and reinstall, and no need to worry about splitting the spindle hole?
If the crank bolts come loose, the issue will be that the tapered square holes in your crank arms will no longer be square. They will never tighten down properly on the spindle again and you'll be constantly having them come loose. You need to get the torque right the first time unless you don't mind buying new crank arms.

Originally Posted by yummygooey View Post
I'll go find a torque wrench and get these bolts tightened to spec ASAP. At this point, I think I do enough of my own wrenching to justify a decent tool set. I'm just trying to gauge how much damage (if any) was done. I've probably only put like 10 miles on these crank arms so I don't think I did anything catastrophic.
Assuming the bolts have not come loose yet, you are probably ok. But you are riding on borrowed time and should attend to the issue ASAP.

Originally Posted by yummygooey View Post
Also, what are your views on greasing a spindle/not greasing a spindle? I've always been told to not grease a square taper, but Sheldon's site suggests otherwise.
I was against greasing until I happened upon a set of arms on my winter bike that almost didn't come back off the spindle. I lightly grease now.
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Old 07-26-11, 09:47 PM
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+1 to everything joejack said.

you should be able to get them pretty close to proper torque with a 6" wrench, the acceptable range is pretty wide.

I don't know your tool situation but if you need more leverage you could use a cresent wrench (or a piece of pipe, etc...) to increase the workable length of your 6" wrench and decrease the amount of ft/lb needed at the handle
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Old 07-27-11, 05:49 AM
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That's a good idea, I will give that a try. I actually have some longer wrenches, but they're all 3/8" drive and I seem to have misplaced my 1/4" adapter. Doh!

I've installed the same model of crank arms on another bike before without a torque wrench and haven't had any problems for about half a year. I think this is all in my head.
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Old 07-27-11, 10:52 AM
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A beam type torque wrench is cheap enough compared to a crankset. Once the bolts are properly torqued they should never be retightened. http://www.sheldonbrown.com/brandt/i...ng-cranks.html
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