Turn the eccentric shaft to the external figure (or the internal figure, depending on the vehicle model) and calculate the number of teeth between the highest point of the intake valve and the exhaust valve cam. The middle point is the camshaft timing mark. Just turn the crankshaft to the top dead center 4 times perpendicular to the horizontal line of the cylinder head, and so does the double eccentric shaft, but it is best to make a mark when disassembling the timing belt first.