Timing with a vacuum gauge
weird. The mark is dead on at TDC. Its a 67 motor with a 73 timing cover and ballancer though. Maybe that's why. The 67s had the mark on the other side of the engine.
So are you saying that the timing marks on damper and timing cover lined up at true TDC for #1 when you were assembling the engine? If that is the case, then the damper ring has not slipped. I read your posts to say that both your timing cover and damper are 1970 and later; as long as the damper and timing cover are the same vintage, the marks should line up properly at TDC, regardless of the block's year.
Do you have the aluminum bodied water pump? (Which is the 1970 and later version) If so, then the timing marks should be visible on your '73 damper and timing cover. Do you have power steering? Sometimes that setup blocks the timing marks on the left side.
If in post #1 you mean that you cannot see the timing mark on the damper versus the timing mark with the timing light after using the vacuum method, then the mark on the damper probably is back under the water pump when the timing light fires. That means either the damper slipped, or your timing method has advanced the idle timing too much and the damper mark is back under the water pump, where you cannot see it.
I never use the vacuum method except maybe to get in the ballpark. I've seen guys end up with 30-40 degrees of initial advance that way. IMHO, there is too much interaction with carb settings to make this reliable.
