The first method is the cylinder-by-cylinder adjustment approach. According to the engine's firing order, once the piston of a specific cylinder reaches top dead center (TDC) during compression, the valve clearances for the intake and exhaust valves of that cylinder can be adjusted. After adjusting one cylinder, rotate the crankshaft and proceed similarly to adjust the valve clearances of the remaining cylinders in sequence.
The second method is the two-step adjustment technique. First, rotate the crankshaft so that the piston of cylinder 1 is at TDC on the compression stroke, aligning the flywheel mark with the inspection hole marking (as in the EQ6100 engine). At this position, valves 1, 2, 4, 5, and also 8 and 9 (in the order from front to back) can be adjusted. Then, rotate the crankshaft one full revolution so that the piston of cylinder 6 reaches TDC on the compression stroke, and adjust valves 3, 6, 7, 10, plus the "two additional" valves (i.e., 11 and 12). This method essentially relies on memorization.
During adjustment, turn the adjusting screw while inserting a feeler gauge between the valve stem end and the rocker arm, sliding it back and forth until slight resistance is felt. Recheck the clearance and repeat until it is correct.
The cylinder-by-cylinder method requires multiple crankshaft rotations and takes more time, but it provides more accurate valve clearance adjustments for heavily worn engines. The two-step method saves time and effort, but requires technicians to remember different valve adjustment sequences depending on the engine model, which can be challenging when dealing with complex or varied vehicle models.