The main problem is when changing the pulley for another which has a different diameter, that puts the TDC mark out of alignment with the marker (which can be off anyway). Remove #1 spark plug and slide and alloy rod into the bore, turn the crank by hand until the pistons stops and scribe a line on the marker inline with the notch on the pulley, then turn the crank the other direction until the piston hits the rod again and scribe another line...divide the space between the 2 lines and you will have TDC....well near enough anyway.