The auto decompressor system is mounted on the camshaft. To set the valve clearence on the righthand side valve lifter (this lifter operates the decompressor system) you have to make sure that the system does not work but that is difficult to see.The system is a kind of camlob located next to real camlob.ook off the valve covers and turned the engine round quickly from the flywheel, seems the loud click is coming from the rhs exhaust valve rocker. As the rocker comes up shutting the rhs exhaust valve it's like a metal clinking.