I've been hearing something about fixing valve lash. By taking of the rocker covers, while the engine is running and tightening.. I guess the rockers?? How exactly do you fix valve lash? What can go wrong with valve lash (like why am I fixing it?)? How can ya do it with the engine running, dont those parts move?
Thanks!

 

For adjusting valve lash on hydraulic lifter motors you back off the nut for the rocker till it starts making noise. Then you just tighten down until it stops making the noise and give it an extra 1/4 or 1/2 turn, slowly. Tightening down too far will cause problems with the valve not closing or striking the piston. Makes a bit of a mess but that's how I've done it.

 

Cartman is correct, and as for the mess, there are clips available that cover the oil holes on the rocker arms, deflecting the oil down onto the rocker instead of all over your engine bay. It makes the job a lot less messy.

The lash can also be set cold, with the engine off. This takes a bit more time, and can be a little more difficult. Perfoming the procedure hot and running assures that all components are at their normal operating dimensions and the lifter is reacting to the oil pressure just as it would whioe driving.