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Old 09-20-10, 01:02 AM   #1
HelsinkiValo
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Left Crank Bolt Issue

I commute to work on a Peugeot Road Bike setup as a single speed. Have had for a few months now. No issue, other than the occasional fluctuation in tire pressure.

Anyway, I tried googling the answer and found a lot of posts concerning loose left crank arms, broken arms, stripped threading, etc. It was somewhat helpful but like everything, this is a case-by-case situation. Here's what's going on:

So last Tuesday morning I woke to find my dad cleaning his bike. He told he had sprayed some WD-40 on my hub to stop the small reaking that had shown up every now & then. It worked. He alsowent ahead and told me he blasted some of it on metal pieces that the crank arms sit/hold on (mind you, I don't know tooooo much about bikes, so I apologize if I don't know the proper term to e used). Anyway, the bike was fine on my way to work,but on the way back........

Halfway back home later that day,while listening to my iPod, I felt a slight wobble on my leg. I thought nothing of it. As I continued for about 4 more blocks the wobbling increased. At this point I stopped, got off the bike and analyzed the situation. The bolt had come loose & not having an 8mm on me, I had to resort to taking the bus home. Left the bike @ home the next morning. I bought a Crank Bros. multi-19 the next day on my way home.

Today was the first day back on the bike. Although not as significant, the bolt keeps coming loose a bit. Can't figure it out. The mounts seem fine,the square metal it rests on hasn't been rounded and they fit snug. The thread on the bolt seems fine. I'm stumped. I have a hunch,do you think theWD-40 contributed & os still the reason I'm having this issue. Any insight on this would be greatly appreciated.

P.S. Sorry about the long-ass post. I just thought you should know the FULL story, so that I may get a proper explanation to my problem. Thanks :-D
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Old 09-20-10, 01:03 AM   #2
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Sorry for some of the spelling errors. I'm typing from my Palm Pre's tiny keyboard and scroll to edit. Sorry.
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Old 09-20-10, 03:32 AM   #3
dabac
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If it's a square-taper cranks, then you have probably stumbled on to one of their few significant weaknesses.
Unless properly torqued at assembly, the crank arm can toggle a little back & forth to the point where it will eventually work itself loose.
The real bummer is that this often messes up the fit between the arm and the BB axle, making it (close to) impossible to get the crank arm to sit right again.
The crank arm needs to be torqued down good, so you're unlikely to get it tight enough with a small handheld tool unless you know what you're doing.

And not having rounded "the square metal" of doesn't say anything. That's steel, and the arm probably aluminium. Their toughness is different by an order of magnitude, so any damage will be to the arm. Not seeing any damage isn't much of an indication either unfortunately.

Bring your bike to a lbs, ask them to tighten the crank to the right torque and hope for the best. If it's still coming loose you can get separate left crank as spare parts.
If you haven't got a lbs within reach, find a guy with a torque wrench (there's bound to be a gear head who works on his own car around) and torque the crank arm bolt to somewhere in the Park Tool recommendation of 305-391 in/lb.
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Old 09-20-10, 12:23 PM   #4
HelsinkiValo
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Heading down on my lunch break to see what happens. Thanks for the advice. ;-)
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Old 09-20-10, 12:37 PM   #5
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you may need to use loctite 's blue on the bolt to keep it from coming lose .
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