I’m going to “blame” LC (Looney Cylinders)  Razz and “thank” KiwiH1A for this post. 

This is one of LC’s post on the Canadian Board (I had just “visited” the Canadian Board last week when I saw it) 

On the inside of the distributor cap there are 4 screws. With a PERFECT fitting screw driver in the slots (with a sharp end too) FIRMLY but carefully back them out. You will likely get only one chance as they are often stuck! DO NOT STRIP THE HEADS OF THESE!!! If you do you will be into hours of trying to drill and re-tap the integral aluminum contacts the screws thread into. To date I have not heard of anyone being successful rescuing a seized screw/cap.

KiwiHiA’s part in this is that he needed a new distributor cap screw last week, so I dug into my parts and had a NOS one for him. But, both of these guys got me to thinking about bad distributor caps. 

I took LC’s statement as another challenge (I think he likes it when I destroy things).  Razz 

Anyway, anybody who has messed with the early CDI systems has probably come across a distributor cap (or two) that has those little screws “seized” and/or the head of them stripped so you cannot get them out and thus making the removal and replacement of the 7mm HT wires impossible – in effect making the cap useless. I have a few of those caps myself and thought I would at least TRY to make them useable. 

The existing screw is a 3mm fine threaded screw with a nice sharp point. Sometimes I have been successful getting the bad ones out and then putting in a NOS screw, but that doesn’t work very often. I’ve tried reverse drill bits, “easy-outs”, etc. in an attempt to salvage the original threads. 

This is what I have now done: I first center punch the head of the screw (or whatever is left of it), and then take a 1/8” drill bit and then just drill out the screw. Obviously, you need to be a little careful with the drilling, so you don’t go into the cap on the “other” side (you can mark a drill bit at ½” and you s/b OK). At this point I have resigned myself to go to a 4mm screw as a replacement. In fact, what I have used for my “prototype” is a carb bowl screw. I believe that is a 4mm x .75 thread. What I intend to do is to see if I can source a 4mm x .75 “low head” or “half-high” stainless steel screw with an allen wrench or torx type head so, IF it ever has to be removed, with that type of a head on it - you should have a much better chance of loosening it than if it were a straight "slotted" screw head (Yes, this is a case where Kaw. "blew it" with a slotted screw head Evil or Very Mad ).  I could really be optimistic and think I can find one already pointed? But, for now, I used the Phillips head carb bowl screw. Obviously, whatever stainless screw I end up using – I will need the correct tap to match. 

There appears to be plenty of aluminum in the cap connecting the rotor contact to the screw hole, so I think the threads will hold OK for the 4mm screw. 

I then took a 9/32” drill bit and drilled through the cap material only – carefully - down until I hit the aluminum. The cap material is soft and will “draw” your bit in fast, so again – be careful and stop when you hit the aluminum. The reason for doing this is so that the head of the screw will end up being “recessed” so the rotor won’t hit it. 

I then carefully removed the little lock washer from the carb screw and cut the screw so it was 10mm long, measured from the bottom of the screw head to the end of the screw. I then took the screw to my bench grinder and attempted to grind a point on it as close to the original screw point shape as possible. I really don’t think the shape of the point is THAT critical, it just has to penetrate the soft insulation of the HT wires, which is pretty easy to do. Likewise, if you end up with a screw length of 8-10mm, I think you will still be OK.   

I put dielectric grease on the threads when putting in the 4mm screws, AND - I also put a coat of soft silicone caulk over the heads of the new screws, to maybe help eliminate some of the corrosive action that takes place in the cap. 

Even with my crude “points” on the screws that I have installed – the wires seem to be held in there quite well and I can’t pull them out.   

If LC (or anyone else) sees a flaw in my method – please let me know why you don’t think this will work. 

Otherwise, when I get done with my ’70 rebuild – I will get out my trusty early “test mule” H1 and see how this cap works. 

If it works OK - I'll try to be around in another 40 years to see if the screws are corroded in there...............