The rocker arm nuts keep coming loose repeatedly for one of three reasons:
- They are stover style lock nuts and the friction type lock is worn out: Replace the nuts
- They are jam style nuts that work against an adjustment screw, they need to be removed, cleaned, inspected for wear and replaced when proven bad.
- There is something wrong in the valve train and the issue is not the nuts but that the valve train is wearing that quickly. This is usually caused by a lack of lubrication due to components being worn out.