I was told last year that an E-mag was not available for the VW engine. A member of the Thatcher list on groups.io shared their success with me at https://groups.io/g/thatcher-aircraft/topic/magneto_drive_on_great_plains/94002510

Original post excerpt:

...But hey, this is experimental aviation and I had a back up ignition (that needed some work too).
The E-Mag does not come with drive lugs on the tapered shaft. So I had made a steel magneto drive lug which extends far enough into the bell housing to allow the use of Steve's 1/2 inch puck which is well clear of the wall and where the drive lugs almost overlap each other. The E-Mag's right angle ignition cable boots clear the firewall by 1/4 inch. I have not yet finished the installation...
P
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P,

Can you share your E-mag story? I was strongly considering one to replace my Bendix dual magneto and was told that they 1) do not come in VW rotation 2) do not have the proper drive lug.
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E-Mag say I am their first VW customer. They set my unit up for the correct rotation and increased the over speed cut out to 3800rpm. I am not sure if the advance curve will be optimum for our wider speed range, but they sent me PC software to shift it, if required.

They no longer make drive couplings, so it just comes with a tapered shaft with castle nut and cotter pin. So I designed a coupler with drive lugs. But to get the exact spacing for the puck, it took a lot of trial fitting onto the taper before it was correct. See photo. E-Mag are developing a dual mag version at the moment. My secondary ignition is off the distributer drive. It works well, but GP did not tell you to take the cover off and apply some friction onto the rotor when you time it. Otherwise when the engine runs, the advance falls back from 28deg to about 22, due a tiny amount of back lash in the drive up to the rotor.
Regards,
P
CX4
South Africa
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Glad to hear they finally created a VW version. Do you have a coupler you could sell me? Or some drawings or CAD files I can use to make my own? Even knowing what material you used and the degrees taper of the shaft would be a big help.

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E-mag adaption:
I used the 4 cylinder Lycoming model. The taper on the shaft is apparently the same as on a Slick magneto, but I don't have dimensions for the taper.
Every different VW conversion will require its own special coupler. The dimensions will vary each time. If your engine has lug coupling on the flywheel, then you can employ a 1/2 inch puck which Great Plains sells, and then develop the dimensions of the e-mag coupler. I used the rear surface of the Diel bell housing as the reference point, since this is where the e-mag mounts.
I have a sketch with dimensions, which I gave to the machinist, but he had to trial fit the coupling onto the taper many times, until its drive lug was the correct distance from the e-mag mounting flange. It was made from mild steel. 6061-T6 would have been lighter, but unavailable in my part of the world.
Limbach uses a different type of coupling made of an elastomer. Grob's engines used another type of coupling, but they would need replacing every couple of hundred hours due to wear, which made the ignition firing point shift. My puck is made from what is trade marked Tufnol.