sorry, my bad. I re-tested #5, compression is 120.
So here is result of the new test (sober test, didn't drink any beer this time).
cylinder 1: 100 psi
cylinder 2: 50 psi
cylinder 3: 95 psi
cylinder 4: 105 psi
cylinder 5: 120 psi
cylinder 6: 100 psi
cylinder 7: unknown, can't get to it.
cylinder 8: 110 psi.
A pop out the exhaust would tell me the exhaust valve on the cylinder with 50 PSI is the problem.
1st thing I would do is verify all the rocker arms are moving and the valves opening. It could be a wiped cam or collapsed lifter....If that is good then check your timing relationship between the distributor and the balancer.
1 way to verify crank/cam timing is to find TDC on Compression Stroke. Line up balancer line and zero on the water pump tag. Then see if the rotor tip is pointed at #1, if so, it is not timing chain.
