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I want to put in a new distributor. My new dampner only has a slot milled in it. There no numbers. When the pointer is aligned with this slot is that 0 degrees? I know I have to be on the compression stroke and I will determine that with a rubber hose and fitting in the spark plug hole and when I feel air coming through the hose I am on compression. TIA.
Yes, the milled slot is supposed to be the 0° mark.
BUT, if it's a new damper, you should check that this mark really matches the #1 piston TDC.
Every timing adjustment you'll do later will depend on this basis.
If it's false and it sometime is or manufacturers wouldn't sell adjustable timing pointers, your timing will be false by the same amount.
You can check that easily by using a piston stop, it's cheap and only takes a few minutes :
The suggestion by 73streetracer about using timing tape is a good one. Alternately you could buy a dial back timing light which is a good thing to have as well.
Because the piston movement near TDC is very gradual (a few degrees either way of TDC), the best way to get an accurate TDC position is with the piston stop tool. There are other 'backyard garage' methods and they will get you within a couple of degrees of TDC, but the stop tool is one the best ways.