Adjust Valve To learn the valve adjustment method, we must first know the basic valve theory. In engine components there are 2 types of valves, namely intake valves and exhaust valves. This valve will work according to the combustion sequence. OK, let's refresh together the sequence in the 4 step engine: 1.Intake Steps In this intake stroke, the piston will move from the TDC position to the BDC position, the intake valve is in the open position and the exhaust valve is in the closed position, so that air will enter the combustion chamber through the intake valve. 2. Compression Step In this step, the intake valve and exhaust valve will both be closed. The piston moves from BDC to TDC to compress the air in the combustion chamber so that the pressure and temperature will increase. The pressure after compression will be 30 - 40 kg/cm2 and the temperature in the combustion chamber will be 400 - 500 degrees Celsius. 3. Power Step In this step, the intake valve and exhaust valve are still closed, the fuel particles sprayed by the nozzle will mix with air which has high pressure and temperature, resulting in combustion which produces high pressure and temperature. As a result of this combustion, the pressure increases by 80 ~ 110 kg/cm2 and the temperature becomes 600 ~ 900 degrees Celsius. 4. Exhaust Step In this step, the exhaust valve opens and the piston will move from BDC towards TDC to push the remaining combustion gases towards the muffler. In conclusion, a 4-stroke engine is an engine that requires 4 piston strokes and two crankshaft revolutions to produce 1 combustion process.