Right side crank keeps coming loose

[Thxcuz]

I don't get it. My right side crank keeps coming loose. Nothing looks stripped and I crank the bolt down nice and tight but after a few miles my cranks gets all loosey goosey. Like the bolt is unscrewing itself.
Has this ever happened to anyone else?

 

[Walker]

if this is a 3 piece crank, make sure the crank arm isn't bottomed out on the spindle. Over time an aluminum crank arm will stretch over the spindle. Sometimes to the point where the bolt is bottoming out on the spindle. if this is not the case, try some blue loc-tite.

 

[jerrykr]

^
+1 on the blue Loc-Tight --- and possibly a thin washer under the bolt head.

 

[Bigcam59]

examine the inside edge of the crank arm. the edges of the hole where the axle bolts in should be square and straight. If it came loose while riding you may have hogged out the square hole a bit. if you did, it will always loosen up as you ride.

 

[user 135]

examine the inside edge of the crank arm. the edges of the hole where the axle bolts in should be square and straight. If it came loose while riding you may have hogged out the square hole a bit. if you did, it will always loosen up as you ride.

+1. The steel spindle most likely rounded out the square taper inside the crank arm. If so, time for a new crank arm.

 

[Thxcuz]

it was actually the crank arm itself. It's a new crank, but a cheap one. It wasn't completely going in. I few whacks with a mallet and a good tightening seemed to do the trick.