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Crank Arm Keeps Loosening

Old 07-31-20, 03:10 PM
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etherhuffer
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Crank Arm Keeps Loosening

I think its fubar. Non drive side, came loose on ride, had LBS tighten and was loose by the time I was 10 miles later. Going to guess the flats in square taper are messed up. Sugino XD600. Can you file the flat down on these or is that wishful thinking?
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Old 07-31-20, 03:15 PM
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I think you are right and it's probably done. Good thing is that a left-side crank is easy to replace, just get the same length and taper orientation, "square" or "diamond" as the old one. It will work even if it is not a perfect match. And make certain to adequately torque the new one (and its mate) so the same thing doesn't happen again.
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Old 07-31-20, 06:27 PM
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Agreed that repeated loosening after retightening is the classic example of the arm's tapered hole being deformed. Trying to file the flats flat will not work, or the various attempts I've seen never have worked out. Replace the arm, torque down properly and revisit the retaining bolt's torque after the initial few rides. Andy
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Old 07-31-20, 06:51 PM
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Yeah, took it off, its deformed. Looking at Sugino stuff, back ordered all over the place. I have an old RSX crank arm to sub in. Ugly fix but hey.....
Can spindle cause problems, anything to look for so I don't kill another arm?
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Old 07-31-20, 08:38 PM
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Originally Posted by etherhuffer View Post
Yeah, took it off, its deformed. Looking at Sugino stuff, back ordered all over the place. I have an old RSX crank arm to sub in. Ugly fix but hey.....
Can spindle cause problems, anything to look for so I don't kill another arm?
No, the spindle isn't the cause; it's caused by riding with the arm not securely fastened to the spindle. When you install the new arm, make sure it is properly torqued to the spindle, and check it again after a couple rides.
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Old 07-31-20, 09:03 PM
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Square taper spindles are made of steel which is much harder than the aluminum alloy crank arms. 99.9% of the time the crank arm has to be replaced

Last edited by alcjphil; 08-03-20 at 11:54 AM.
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Old 07-31-20, 10:03 PM
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OK. Searched for single crank arms. Sugino line up/quality is a bit opaque. Can I get an RD, Messenger, Mighty, etc in lieu of the XD? This is for touring bike and while I am over 200 lbs I don't break stuff. This fubar must have been from me during the build as bike has less than 500 miles on it. Found a spare RSX crank for a temporary kludge fix
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Old 08-01-20, 02:09 AM
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I save the odd crankarm by crazy-gluing a piece of soda can on each of the flats of the spindle. Maybe not a permanent fix but it should work until you source and receive a replacement crankarm.

Cheers
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Old 08-02-20, 11:43 AM
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I had this happen at Burning Man last year. Solved it by having an itinerant welder put a spot weld between the spindle and retaining nut. When I got home I trashed everything, cranks, and spindle and replaced with another new used set.

I was thinking that some blue lock tight on the retaining nut/bolt might work for a while. Blue lock tight on the spindle taper before assembly might work for a while. Red lock tight on everything might work for longer than you want it to.
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