Determining top dead center

First off, the large round hub on the front of the crankshaft is called a harmonic damper by some and a harmonic balancer by others. If it is bolted to the crank of a 350 Chevy that is internally balanced, then it serves only the function of being a harmonic damper, dampening vibrations set up in the crankshaft as a result of the rod journal springing back and forth from the forces applied to it during operation. Unless the motor has been unaltered and is "as built" by the manufacturer, you have no idea if the TDC notch on the ring matches the timing pointer attached to the block or front cover, even if the outer ring has not slipped at all.  

First off, the large round hub on the front of the crankshaft is called a harmonic damper by some and a harmonic balancer by others. If it is bolted to the crank of a 350 Chevy that is internally balanced, then it serves only the function of being a harmonic damper, dampening vibrations set up in the crankshaft as a result of the rod journal springing back and forth from the forces applied to it during operation. Unless the motor has been unaltered and is "as built" by the manufacturer, you have no idea if the TDC notch on the ring matches the timing pointer attached to the block or front cover, even if the outer ring has not slipped at all.  

There are a multitude of different dampers and three different timing pointer locations on a Chevy. I don't know about other brands. Chevies use 12:00 noon, 2:00 O'Clock and 2:30 O'Clock and if anyone has had the motor apart, you don't know if they used the original damper and timing pointer or other swap meet parts when they went back together with the motor. The whole reason for doing this operation in the first place is to be able to time the motor with a timing light and know, absolutely, that the timing is correct. The elastomeric material that connects the outer ring of the harmonic damper to the inner hub which presses onto the snout of the crankshaft begins to break down over a long time due to ozone in the atmosphere and oil and fuel which may find its way onto the material. When this happens, the outer ring may slip in relation to the inner hub, rendering any attempt to time the motor with a timing light futile. Even though this operation you are about to do will bring the timing marks back to correct for the time being, there is no guarantee that the ring will not slip further after a while. If you want to bulletproof the operation, then start with a new or rebuilt damper and use the correct timing pointer for that damper.  

There are a multitude of different dampers and three different timing pointer locations on a Chevy. I don't know about other brands. Chevies use 12:00 noon, 2:00 O'Clock and 2:30 O'Clock and if anyone has had the motor apart, you don't know if they used the original damper and timing pointer or other swap meet parts when they went back together with the motor. The whole reason for doing this operation in the first place is to be able to time the motor with a timing light and know, absolutely, that the timing is correct. The elastomeric material that connects the outer ring of the harmonic damper to the inner hub which presses onto the snout of the crankshaft begins to break down over a long time due to ozone in the atmosphere and oil and fuel which may find its way onto the material. When this happens, the outer ring may slip in relation to the inner hub, rendering any attempt to time the motor with a timing light futile. Even though this operation you are about to do will bring the timing marks back to correct for the time being, there is no guarantee that the ring will not slip further after a while. If you want to bulletproof the operation, then start with a new or rebuilt damper and use the correct timing pointer for that damper.