Is the valve adjustment critical?
Not at all, this contributes to the reliability of Laser engines. In practice you simply set the valve clearance so there is slight movement of the rocker. You do not even need to use feeler gauges. The setting is unlikely to alter for many hours running. There is an oilway from the crankcase through the pushrod covers into the rockers. If the engine is inverted (most are!) the rocker cover will fill with oil which is ideal for lubrication.
