Crab distributor rotor contacts cap

[GB SISSON]

I have been having trouble with a couple of rotors that hit the contacts inside of the caps. I am away from the shop for a week and so I couldnt investigate much before I left. The engine has a 3 bolt cover and a spacer kit by the PO. It quit running and I found brass dust inside the cap and slot on #7 contact. Installed a different cap and rotor that looked good but used. Same thing occured. Next I installed the Bubba dist cap and rotor I had bought for my woodie. Two days later it sounded like it had a miss. I pulled each wire and obvious #7 was dead. Followed that wire back to the distributor only to find the bakelite nipple had broken clean off #7 and was dangling still attached to thr plug wire. This distributor had worked perfectly on the woodies 59ab running on a stand and the rotor and cap are new Bubba issue. The night before this trip I wanted to park this truck in its shed so I took yet another rotor and cap and ran the rotor against the belt sander to get more clearance, installed it and drove it inside. I Acan only assume a problem with the spacer??? I know about the offset tang and am careful about that, and it bolts up nicely. I have not detected any side play in rotor shaft. What is up? Internet is harder than at home but I welcome ideas if you dont hear right back. Thanks in advance

[Charlie ny]

GB,
Hold on..........I'm just a little guy but I build a ton of front mounted distributors and they all have a common problem, that is the fit and location of the big bushing on the timing cover end. When I build a crab distributor ,after disassembly ,I machine the bushing diameter on the rotor shaft to insure it is straight and round.....usually this dia is at least .005 tapered and or out of round. #2 I press the standard worn out bushing out of the housing. I then press in an undersize (on the inside dia) bushing into the housing.
I set the housing up in my lathe holding it by the diameter that the cap seats on. Doing it this way I know that after finish boring the inside diameter of the bushing
will be on the same centerline as the diameter on the housing that the cap seats on.
I bore the undersize bushing to fit the particular rotor shaft that I have made straight and true. The housings are ALWAYS warpped or stretched to the extent I seldom get a full cut during the boring operation until I've removed .025 or .,030 from the ID.
I will say there is no sense in pressing in a standard bushing and running a worn
rotor shaft diameter in it. From what I've seen very very few housings have critical diameters that are even close to concentric.
It's pretty rewarding after finishing one of these babies to be able to pop the rotor and cap in place and know with confidence there will be no interference.
I'm pretty sure your spacer kit is OK.
Charlie ny

[Drbrown]

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Charlie ..... Thanks for the description of the methods you use for rebuilds. I appreciate the careful analysis you've done to arrive at your process.