Power Valve Bolt Keeps Loosening

[cnrcpla]

The bolt that connects the push rod and the powervalve itself. Its the number 5 screw here:
http://www.cmsnl.com/yamaha-yz250d1-competition-1992_model9919/partslist/B-07.html#results

I tried cleaning it, making sure everything else was functioning properly, nothing is broken and everything is in spec. It was fine until i took a long trail ride and it just randomly stopped working. I took the cover off and saw the bolt backed all the way out. Even when I screw it in really tight (not to tight, I don't want to mess up the threads) it'll come loose now within 10 minutes of riding. It literally backs all the way out and then the slotted metal piece pops off the power valve and renders it useless. While I have it appart for the third time I'm doing a top end, so I got a few days to mess with it. I'm just at a loss right now 

[_X_]

loc tite, the weak stuff green i think.

[LukeG]

If you can, run a tap down the hole to help clean the threads thouroughly, then medium strength loctite will hold it in place.

[SachsGS]

Buy a new, high strength bolt as well.

[cnrcpla]

Alright, I'll be picking those things up with my new piston. I was just worried it was getting snagged on something. Seemed like such a random out of the blue thing that happened. Thanks! 

[TMKIWI]

Make sure you clean the bolt thread and where it threads into with something like brake clean to get rid of all the oil before you loctite it.