Crankset keeps on unscrewing

[lstelie]

Hello,
My bike as a M443 Shimano (low end) crankset , with a Deore front derailleur and a Deorre XTR rear derailleur.
The crankset doesn't stay screwed on. every 50/100km I have to fix it. Any body has an idea about what I may want to do ?
As a side question, my crankset is secured in the opposite rotating direction, so when I ride it is normal that I slowly free it, is it normal ?
Thanks in advance

[DaveM]

I'm not 100% sure if you mean that the crank arms are coming loose or that the bottom bracket (BB) is unscrewing itself out of the frame.
If the crank arms, it could either be that you are just not tightening them enough (I'd recommend finding a shop that can tighten them with a torque wrench to get it right. Or it could be that the arms are damaged and may need to be replaced.
But I think you mean that the BB is coming loose. Again, it could be that you just aren't getting it tight enough, but these don't really need to be cranked down that hard. Is it coming loose just on one side? Some lower end BBs have a plastic cup on one side and that cup can get mashed out of shape. This will allow a little bit of movement in the BB as you pedal which could cause the cup to unscrew. You may be able to just replace the cup.
On the drive side, I think it is always metal threads which shouldn't have this problem unless the threads are completely stripped.
If you can't see any obvious damage, you could try a little locktight on the threads. But nothing too permanent, you will need to remove this someday. Otherwise, either try replacing the plastic cup or whole BB. The drive side of the BB has reversed threads (rightly loosey), the left side is normal threads. This is standard.