Part of my rebuild was to replace the original distributor with a Mallory, because I was going with fuel injection. Anyway I bought a new gear for the shaft on the Mallory distributor and installed it. Put it into the tach drive housing and the offset dog (slot) was very tight. I started removing material on one side of the slot in the gear only to find the real problem. The bore in the tach drive housing was eccentric to the dog shaft. I found a good used tach drive housing and bought it only to have the same problem. The PO or the factory had opened the slot up to adjust for the eccentricity. The problem with that is about half of the rotation there is a looseness in the engagement and the other portion it is ok.
So I decided to fix this for good. Having owned a machine shop and still having several machines I decided to machine the housing. First I machined a set of soft jaws, indicated the housing in and it showed the housing was eccentric by .004" tir. So I machined the housing so that I could install a brass insert. I pressed in the insert and then machined it back to the right dimensions. Now everything is concentric and the distributor fits great.
John
So I decided to fix this for good. Having owned a machine shop and still having several machines I decided to machine the housing. First I machined a set of soft jaws, indicated the housing in and it showed the housing was eccentric by .004" tir. So I machined the housing so that I could install a brass insert. I pressed in the insert and then machined it back to the right dimensions. Now everything is concentric and the distributor fits great.
John