I got a 3.0 vulcan. I changed the head gasket and put back together. only had 30 psi average compression for the cylinders. I took it all back apart and found the valves were very leaky. I put the heads on and have 170psi. I put the rocker arms on and have 0-25 psi. The rocker arms won;t back off enough. I tightened the rocker arms to 25 ft\lbs as recommended. I can't adjust them. what do I do? can I shim the rocker arms?