This is not on my jet boat, but on my 1972 Plymouth Satellite 400cid, 4 barrel. I had the engine recently rebuilt and have developed what sounds like a knock on the #5 cylinder. I read that you can determine if it is a rod knock by pulling the plug wire and eliminating the detination allowing for the piston to stop knocking assuming that it is a bad rod bearing. When I do this I notice that it does quiet down but does not go completely away when the plug wire is disconnected on #5. When I hook it back up it comes back. With all plug wires conected It is louder at low RPM's and seems to diminish when I raise the idle. I read that a rod knock gets louder at higher rpm's. confused and ???? further I do not know if he primed the oil pump I did not since the timing chain was on already when I got the motor.