CHECK AND ADJUST VALVE CLEARANCE

Too little valve clearance throws its out of time. It open too early and close too late. This causes the valves to overheat due to hot combustion gases rushing past valves when out of time. Overheating lengthens valve stems which prevents proper seating of them. Them seat so briefly or poorly that normal heat transfer into the cooling system does not have time to take place, causing burned them and low power.
Too much of them clearance causes a lag in valve timing causing engine valve train imbalance. The fuel-air mixture enters the cylinders late during intake stroke. The exhaust valve closes early and prevents waste gases from being completely removed from cylinders. Also, the they lose with a great deal of impact, which may crack or break the it and scuff the camshaft and followers.
NOTE: It clearance should be checked with engine cold.