[madmaxx]

There is never an excuse for a fastener to loosen. Fastener technology has been around for 1000's of years, LOL!!! Never had a fastener loosen on my Envoy, Lexus, gmc truck, bonnevilles, cadillacs, triumph spitfire, miata's, oldmobiles, mercruisers, mercury's cheverolets, I would guestimate 40 cars and 3 boats. I did have the carburator come loose on my sears crafstman blower one time, so I guess it is possilbe. It was covered under warranty.

Loctite is only one solution, there are different types of nuts etc.

Do we really know if a fastener loosened in this instance? The nut came off so did we find the nut? Not familiar with this valve train set up is the culprit set to a predetermined torque value or is it adjusted with backlash? I doubt something was left loose, wonder it something else is not going on, excessive deflection, vibration, thermal cycling etc.