How much play should there be between the distributor drive gear, and the housing on a TO-30?
The maximum clearance between the bottom of the distributor housing and the drive gear is 0.010″. If you are going to reset or replace the drive gear, you might as well rebuild the distributor.
Steiner’s sell a rebuild kit for the distributor which includes the bushing, shims and spacer washers for $22.95. The Steiner part number is ABC3007. They also sell new clips for the cap, the side terminal assembly as well as the cap, rotor, and dust cap.
The drive mechanism and advance mechanism has a top and bottom half. Once the points, condenser and side terminal are removed the inner plate can be removed by removing three screws. This will expose the advance mechanism. Once the nut locks are opened and the nuts and springs are removed, the top of the shaft and the weights can be removed.
Remove the distributor from the block. Remove the screw in the side of the housing and drain the oil. Drive the rivet from the drive gear to remove the drive gear, and remove the shaft from the top of the distributor. If there is excess play indicating wear in the bushing, it can be pressed out and replaced. Be careful pressing the new bushing into the housing. A mandrel or suitable metal dowel should be used to keep from distorting the bushing. After the new bushing is installed, install the shaft with a spacer at the top and bottom, and a shim or shims at the bottom to keep the end space between the gear and the bottom of the housing under 0.010″ when the rivet is installed.
Refill the oil reservoir with 20 weight oil and install the screw plug. Lubricate the weights with a light coating of 20 weight oil. Lightly oil the top of the shaft. Lightly oil the felt plug, and place it in the top of the shaft. Do not over oil. Over oiling the advance mechanism and top of the shaft will foul the points and inside of the cap.