External Motoplat vrs Amal SEM

On disassembly of my 84 250 WR I noticed that there was some Carbon looking material laying in the bottom of the case. Closer inspection shows that some of the Magnates are braking loose inside the Flywheel. E-bay is full of Motoplat Rotors but not SEMS. I see they are not interchangeable as the SEM is larger in Diameter. So what controlled which unit a WR Bike came with ? Was it just random, some were Motoplats and some were SEMs ? Yes I understand that the CR and XC used the internal Rotor Motoplat.

The WRs from 1982 on were spec'd from the factory with SEM ignitions. Because some units were faulty many were replaced with Motoplat Mini 6 external rotor units. I have the same problem with the SEM in my 84 250WR. I have heard there was a problem with the adhesive that hold the magnets in the rotor that seemed to affect mostly 1984 model units. The magnets can be reset with epoxy. If you can repair or get an SEM ignition with a good flywheel( bad stator), there is a chance the stator is usable.

Thanx for the Heads Up. Maybe I will give the epoxy fix a Try, I have nothing to loose.

XCs came with external rotor Mini 6 Motoplats, not internal like the CRs.