Were and what are the timing marks on a Nissan 1991 240 sx?

The timing marks are on the crankshaft pulley. It is visible as you look at the right hand side of the engine. Use a flash line on the pulley to see it better. The pulley has indentations on its outer perimeter or edge. I think there are about 4 or five indentations. There is a sharp round metal pointer on the engine block which is perpendicular to this pulley as the engine runs. Once the sharp round marker is within the range of these indentations it means that the rotor of the distributor is giving spark to spark plug No. 1. This means a spark to the combustion chamber of piston no. 1 is being fed by this spark plug to create an explosion which moves the piston down. Spark plug no. 1 and the metal round pin pointing to the indentations is the start of the firing sequence of the engine. In this case firing sequence 1-3-4-2 . The rotor fires spark plug 1 then 3 then 4 and finally 2 giving the full cycle of the engine. You have to then fine tune the idling of the engine by rotating the position of the distributor a little to the left or to the right. A timing light should be used to confirmed if the timing if perfect. Alex