If the valve clearance is too large, then part of the pushrod and camshaft stroke will be spent on compensating for the excess clearance, i.e. the valves will not be open long enough. This will have two effects: the valve drive mechanism parts will make a knocking sound, the engine will run poorly, because the intake valve will not open enough and less working mixture will enter the cylinder. Insufficient opening of the exhaust valve will lead to excess exhaust gas pressure in the cylinder, which will prevent 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 tightly in the cylinder head when they are closed. When a valve is seated in the cylinder head, it does two things - it seals the combustion chamber so that no gases can escape from the cylinder, and it cools itself by absorbing some of the heat from the combustion process into the cylinder head and the engine's cooling system. So if the valve clearance is too small, the engine will run poorly (because gases are escaping from the combustion chamber), and the valve will overheat and warp (because it cannot transfer heat until it touches the valve seat in the cylinder head).
CAUTION: While all valve adjustments should be made with the utmost care, it is better to have a looser adjustment than a tighter adjustment, as burnt valves are the result of a tighter adjustment.
Valve clearances must be checked/adjusted periodically during vehicle operation, as well as after engine repairs related to the valve timing mechanism.
Adjusting the clearance involves turning the valve adjusting screw until the required clearance value is achieved.
ATTENTION: The clearance must be checked and adjusted on a cold engine (engine coolant temperature is 15-25°C). At this temperature, the valve clearances should be 0.15 mm for the intake and exhaust valves. When the engine reaches normal operating temperature, the clearances will increase to 0.2 mm. The adjustment sequence is given for each engine type in the section "Engine repair without removing it from the car".