I was reading in the factory service manual and it talked about making sure the distributor gear goes back on exactly like it came off. Like why does it matter. Cant the distributor rotate? also what holds the distributor in on a 49' flathead.

 

The relationship of the drive-pin to the gear teeth is not exactly symmetrical, so if you install it 180 deg. from original the distributor may be 10 - 15 deg. off. That may mean the advance unit hits the thermostat housing when timing is set, or it may be pointing towards the radiator.

 

Ross, I am lost on that. If its not symetrical how would you get the pin in the hole. If you managed to..... how do you get 15 degrees off from 180 degrees on the gear?

 

The distributor gear has 11 teeth. Say that the hole for the roll pin aligns with one of those teeth on one side, then it is between two teeth on the other. So if you spin the gear 180, you are automatically 1/2 tooth off on your timing. Or the timing would be 360/11/2 = 16.36363636363636 degrees off if you want to be precise.

 

Ross, I see you have been doing your math homework. 16 degrees is not much and if it hit anything you could pick up the distributor and set it a notch over. You are right about the pin and the tooth, I dont have a mark to check mine but see if this if right, the hole aligned with the tooth faces the flat on the top of the shaft that holds the rotor.