Set the TDC according to the marks on the intake and exhaust valve timing mechanisms (when installed according to the mark on the crankshaft pulley, the piston of either the 1st or 4th cylinder may be in this position). After this, be sure to check that the marks on the crankshaft pulley and the lower timing belt cover match. If the mark on the crankshaft pulley does not match the mark on the cover, then the valve timing is out of alignment (piston of the 1st cylinder is not set to TDC). In this case, it is necessary to remove the timing belt and turn the crankshaft until the marks are aligned.
The marks on the intake and exhaust camshaft timing mechanisms must be located in a horizontal plane and directed towards each other, as shown in the photo...
...and the mark on the toothed pulley of the crankshaft must be aligned with the mark on the oil pump housing. The mark becomes visible after removing the crankshaft pulley. The rectangular mark on the oil pump housing must coincide with the risk on the toothed pulley of the crankshaft.
In addition, a mark (cutout) is applied to the edge of the crankshaft pulley groove for driving auxiliary units and to the lower cover of the timing belt.
[The article was reprinted from the website chevyman.ru]