The pinging sound sounds bad. I'll bet it's the piston hitting a valve. If I were you I would pop off the tank and valve cover and take a look at the valves. I'll bet one is hung open OR your cam timing is off. Be sure you figure out what's going on before you take the head off because you need to know the cause of the problem before you fix anything. Once you find the cause I would personally send the head to a trusted machine shop and let them do the work on the head, then you can replace any other worn out parts yourself if you like. A machine shop will have the special tools and experience for doing head work and IMHO it's worth the money. I doubt it's the comp release simply because I don't think the comp release can hold the valve open far enough to hit the piston. Someone correct me if I'm wrong.