If you have to keep adjusting the rocker nuts down to get your settings right, or to make the valve train noise go away, you could be losing the cam or lifters. What type of cam is it?? The only type of cam you need a button with is a roller cam. A flat tappet cam will not walk under normal circumstances. The lobes are angled slightly so that the rotation against the lifters keeps pushing the cam towards the back of the engine. If it truly is hitting the timing cover, something is drastically wrong. And if you have to keep adjusting valves, the cam or lifters are on the way out. You have to do more checking. Are you using standard rocker arm nuts or locking type? If they're the old standard nuts, they're only designed to use once, and they can lose their holding capacity. They might be loosening up. Either try new nuts (they're cheap) or if they're locking type, there is a problem. What makes you think the problem is in the cam walking? It's possible, but very unlikely. Keep us posted. John