If the valve clearance is too large, then part of the stroke of the pusher and camshaft will be spent on compensating for excess clearance, i.e. valves are not open long enough. In this case, two effects appear: the parts of the valve drive mechanism will make a knocking sound, the engine will work poorly, because. the intake valve will not open enough and less mixture will enter the cylinder. Insufficient opening of the exhaust valve will result in excessive exhaust gas pressure in the cylinder, which prevents the required amount of working mixture from entering the cylinder.
If the valve clearance is too small, the intake and exhaust valves do not fit snugly in the cylinder head when they are closed. When the valve sits in the cylinder head, it performs two functions - it closes the combustion chamber so that no gases can escape the cylinder, and it cools itself by absorbing some of the heat from the combustion process by the cylinder head and engine cooling system. Thus, if the valve clearance is too small, the engine will not run well (due to the fact that gases exit the combustion chamber), and the valve will overheat and deform (because it cannot transfer heat until it touches the valve seat in the cylinder head).
WARNING: While all valve adjustments must be made with the utmost care, it is best to have more «free» adjustment than more «squeezed», since burnt valves are the result of more «clamped» adjustments.
Valve clearances must be periodically checked / adjusted during the operation of the vehicle, as well as after the repair of the engine associated with the gas distribution mechanism.
The clearance adjustment consists in turning the valve adjusting screw until the required clearance is reached.
WARNING: The clearance must be checked and adjusted when the engine is cold (engine coolant temperature is 15-25°C). At the specified temperature, the valve clearances for the intake and exhaust valves should be 0.15 mm. When the engine reaches normal thermal conditions, the gaps will increase to 0.2 mm. The adjustment sequence is given for each type of engine in the section «Engine repair without removing it from the car».