MSD crab cap

After converting to electronic ignition I experienced a problem that has plagued others: carbon tracking inside the distributor cap. I had often wondered if the MSD crab cap would fit the Ford distributor and was encouraged when I was told it would. As I was now forced to replace my cap I bought a MSD cap (8541) and the rotor (8567). The cap is the same as the Ford in most of the important dimensions and there was an instruction sheet with it showing a picture of the 8541 as the new design and a picture of an 8537 number as an obsolete version. The 8537 looks exactly like the common black crab caps with the coil connection pointing horizontally toward the driver's side. It looks like MSD needed a crab cap for an earlier application and just used the available Ford part and then later redesigned it. The new design has barrier rings and ridges inside to increase the surface distance between terminals for arc suppression. The rotor also has a barrier around the tip.

The cap was a snug fit to my distributor and even has the receptacles built in for the spring clip retainers along with two ears with holes for screws to bolt down to the MSD distributors. The rotor however is too thick to fit between the distributor shaft and the cap. The MSD distributor for the 48 and earlier Ford V8's are longer than the Ford distributors and there's room in them for a thicker rotor. The Ford rotor can be used with the MSD cap, but I have had trouble with one of them breaking and they seem to fit rather loosely on the shaft. So after doing a lot of measuring and template making I found by removing sixty thousands from the bottom of the MSD rotor and another ninety thousands from the top ridges there was now enough clearance for it to fit. I also removed about seventy-five thousands from the mounting surface for the brass rotor tip to move it down some. And I replaced the steel screw that holds it on with a nylon one, as the screw now came too close to the bottom of the rotor and would probably short out to the brass adapter that mounts the rotor to the shaft. The head of the screw (a 10-24) had to be trimmed down some too, for clearance.

Left side view,cap on dist.<BIG></BIG> inside view <BIG></BIG>

The adapter is about the same thickness as the length that the distributor shaft extends up from the bushing and has three buttons that match the center hole and two of the outer holes in the bottom of the rotor. It is located and held to the shaft with an 8-32 set screw. The vertical coil connection on the cap was a problem in my car as the fan I was using would have hit the coil tower. I was able to get around this problem by spacing the fan out closer to the radiator.

Adapter for rotor <BIG></BIG>

The cap uses "HEI" style wire terminals; I found them and the boots at my local NAPA store or you could buy them along with the cap from MSD under part number 8848. I found to install them they should be crimped to the wire ends and then pushed into the boots. I cut down an old screwdriver to push the terminals into the rear of the boots with a little WD40 for lubrication.

MSD boots and terminals <BIG></BIG> Terminal tool <BIG></BIG>

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