I've got a HT3813 mower that I'm working on. The water pump pulley was worn so I am replacing it as well as the timing belt. However, there are 2 pairs of timing marks on the camshaft pulley. Each pair is 180 degree apart but each has 2 individual marks that are one tooth apart. One is marked with a T and the other is marked with an F. Which mark do I line up with the frame mark, T or F?