Can anyone tell me about the timing mark tab on a 65 OLDS 330 Engine?
I am confused where 7.5 degrees BTC is.
Facing the engine, standing at bumper there are 3 slots on the tab
Slot on left has a square hole under a round hole
Slot in the middle nothing
Slot on right has one round hole
Where would 7.5 degrees BTC be?

 

The round hole is a zero, as in 0 deg or top dead center. The "square hole under a round hole" is actually a one and a zero, as in 10 deg BTDC. The center slot is between 0 and 10, so it's 5 deg BTDC. 7.5 would be halfway between the 5 deg and 10 deg marks.

 

Thanks Joe
It was to simple to spot. Engine runs alot better now with correct timing.