Crank arm slippage
 

So my non drive side crank arm keep coming loose while I ride. I tighten it as hard as i can, but if i go tighten to hard the crank arm starts to click when i put a lot of pressure on it. But when its not tightened to the max, the bolt comes loose after about 5 mins of riding.

Anyone know what may be causing it? Its a sugino messenger by the way. Thanks

One possibility is the taper has worn out due to many removals/installations with too much torque tightening it, or perhaps by not tightening it enough. The bottom bracket taper could also be damaged, but it's most likely a bunk crank taper. Sorry!

You can try some blue threadlock on the bolt.

I know this is stupid, and it's a long shot, but is your pedal in all the way? If not you may be stripping it. Probably not, it's probably something suck ass. Get an estimate from LBS then go do the work yourself after they tell you what's wrong.

probably rounded out the square taper on the crank arm itself,as mentioned in first response. the bb axle should be fine since they are pretty solid, but if it is rounded at all, replace it.

ya ive actually looked at it before. bb is fine, the crank arm though is rounded out

Next time, most (decent) cranks come with torque recommendations, or you can call/look online and find them. If you tighten cranks too much you'll push them too far into the spindle and deform them, and if you don't tighten them enough, they'll flop around on the spindle and round out.