So I was putzing around underneath the hood today tidying up some wiring and noticed that there appears to be 2 timing marks on the pulley for my slant. What is the purpose of this? Rotating clockwise, which is the TDC? Engine runs fine, I'm just trying to fill in some knowledge. Couldn't find any mention of it in my shop manual or here (except to say that people know there are two marks).

Later engines had three marks on the damper, 120 degrees apart. This was for the magnetic pickup the diagnostic computers of the day, used to check timing.
Only way to find out which one is really TDC is to manually put the engine at TDC and see which mark lines up. I recommend putting some paint or white out on either side of the timing mark so you know which one is "THE" mark.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

My 79 engine has three marks on the balancer. I made my own pointer to align with one of the marks so that I could set the timing from the passenger side (alternator is mounted on the driver side and blocks the view of the 'usual' timing mark).

_________________
-MattMan
LEANED & MEAN

Geeze, Matt, that's really nice work! Looks as good as a high-endy factory piece. Can you walk us through how you made it (marks, stampings, finish, etc)?

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

thanks all! Guess I'm sighting the #1 intake through the oil fill to see which one wins the lottery.

Dan and all-

In the 80s, on vans there were factory second timing tabs (I can confirm for the V-8 engines, I can't speak for the slant) that were read from below. The noses on the vans were so short and the belt drive system and radiator fan shroud so obscuring that it is physically impossible to read to stock timing tab marks on the timing cover. The solution was a second timing tab that bolted to the timing cover (maybe the oil pan bolts) that was read from below. Matt's timing tab looks very similar to the factory V-8 piece.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

On the dampner with 3 "timing" marks. TDC is the one were the line crosses the pulley groove.