I have had luck in the past, finding a large, conventional socket, that will fit over the ratchet nut in such a way as to grip it enough to torque the nut. It ain’t pretty but it works. Don’t ask me what size I used, because it’s been a long time since I torqued a KE3 or Mark 5 flywheel….I don’t currently have one, but a large 8-point socket would likely be ideal.
Long live American manufacturing!
