Ok, now that makes sense.Well, the front and rear e28 motors are different. Is it possible that Bmachine has a front? I've got e28 rears in my e9 and they work great; however, I've never seen what an e28 front looks like. Maybe the protrusion of the gear is part of the difference.
The e28 one I have is a rear I got from Don. I compared it with HB Chris’ via photos and they all look the same in terms of how far the gear sticks out from the mounting points on the body.
Jay, (or anyone else who has done this), did you actually check to see if the motor gear actually extends all the way to the full width of the regulator teeth? (See photos above). I am sure that this setup would actually “work”. At least until the bottom 2/3 of the regulator teeth start to wear out. But maybe that never becomes an issue...
The other possibility is that the late 73 / 74 regulator (which is quite different from the previous versions) mounts the motor slightly further away.