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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 01-02-02, 08:45 PM   #1
mike
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Can you over-tighten a crank arm?

Oops. I might have overdone it.

Is it possible to overtighten a crankarm?

The crank is aluminum. The BB axle is steel. The crank arm came loose, so I decided to "enhance" the design and put a lock washer on before the crank bolt.

Then, I really reefed on the socket wrench to tighten the crank arm. It seemed to give just a bit more than I expected. Now, maybe it is my imagination, but the crank seems a little stiff or draggy.

Did I push the crank too far onto the axle? Is this possible?
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Old 01-03-02, 08:52 AM   #2
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Yes indeed, you can overtighten a crank bolt. The exception to this is with the Shimano splined end BB; it's almost impossible to overtighten with those.
John
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Old 01-03-02, 09:02 AM   #3
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With overtightening, you can possibly shear a bolt, or force a loose fitting taper all the way on, so the spindle end is flush with the end of the tapered hole.
Im not sure what role grease plays in helping/hindering damage; consult your local religious leader for more details.

With splined systems you can cause damage. One of the systems (Shimano or Isis) uses a faced end to the splindle splines, the other, a tapered end, which can distort the crank if over-torqued.

There should be no need for excessive force. I make judicious use of foot power on the end of a spanner. Can you tighten to the correct torque by hand?
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Old 01-03-02, 09:06 AM   #4
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Can you tighten to the correct torque by hand?
Ouch. I think I know where that came from.

What is the torque supposed to be? I heard something like 25 to 30 pounds.
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Old 01-03-02, 09:20 AM   #5
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Shimano technical support told me to tighten the crank on their splined spindle to 50 Newton meters (that's pretty tight!). Campy recommends 39 Newton meters on their tapered spindles. John
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Old 01-03-02, 10:00 AM   #6
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This ties nicely with an earlier post about the use of torque wrenches on bicycles. Although I have always tightened cranks by feel, crank attachment seems to beg for a torque specification. Thanks for the Shimano and Campy data, which is probably in the right range for other brands, as well.
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Old 01-03-02, 12:14 PM   #7
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Thanks John! I am buying it no matter what anyone says.

Cheers...Gary
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Old 01-05-02, 04:01 AM   #8
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Campy also advises NOT to use any lubricant on the spindle flats, in fact it is also advised to CLEAN all crank/bottom bracket contact surfaces THOUROUGHLY using clean cloth and Acetone.

Ride A Little Tight
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Old 09-02-07, 10:24 PM   #9
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do i have to buy one of those park torque wrenches to make sure my cranks arent on too tight? how much can i safely tighten with a 6 inch crescent?
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Old 09-02-07, 10:54 PM   #10
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Originally Posted by prufrock View Post
do i have to buy one of those park torque wrenches to make sure my cranks arent on too tight? how much can i safely tighten with a 6 inch crescent?
Any torque wrench coupled with a 14 or 15 mm socket will do the job. If you're doing it by hand, you'll have to use 'feel'. First make sure everything is assembled correctly, ie, everything is clean, bolts are greased, no burrs, etc anywhere on mating surfaces, and then tighten away. The goal is to get it tight but not too tight. You want it tight but you don't want to distort the aluminum holes in the arms. Unfortunately, too loose can also cause damage if the arms start rocking back and forth on the spindle. As a general rule of thumb, once the resistance level reaches a plateau, you're probably there.

Of course, all this only applies to square taper systems and only if you're re-installing the cranks for whatever reason.
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Old 09-02-07, 11:50 PM   #11
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I have a UTICA 3/8" driver beam type, 0-600 in lb for this particular application. Cost me $15 on Amazon, although that was probably a special (can't find it now). Looks suspiciously identical to one of the Park models. I'd hunt for specials online, eBay, etc.

Last edited by sfrider; 09-02-07 at 11:58 PM.
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Old 09-03-07, 08:22 AM   #12
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Overtightening the crankarm onto the BB axle shouldn't increase friction in rotation unless the inside of the crankarm is actually now rubbing against another part. It shouldn't be touching anything except the axle.
Most references suggest never greasing square tapers. All references say to grease splined axles
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