Need help!! Had a coolant leak (famous 3.1L GM ? 96,000 km) from lower intake manifold gasket. I replaced that gasket and both head gaskets at the same time. When I put everything together, engine misfire on #6 cylinder. Heads are OK, valves are OK.(checked by professional shop) Problem is when exhaust valve rocker is tightened properly there is misfire and loss of compression in that cylinder. If I loosen up the rocker it works fine but it starts to make clicking sound after a while. I changed lifter and pushrod ? same thing. Where is the problem ? do I need some sort of a shims between the rocker and pedestal to get the correct preload on the valve. Could it be valve spring???