Whilst it's tempting to think you are going to be able to lift the engine out of the frame without dismantling the engine plates and the footrests, don't bother. These bikes are so simple that you might as well pull it all apart. When you do, you can give it all a clean and attend to any problems you didn't know you had
First job is to get it all in the parts washer and give it a good clean. It's impossible to inspect anything if its covered in grease and road dirt
The crankshaft gear is a little stiff - you will need a puller to remove it. This one is made from a bit of 1" x 3/16" equal angle, with three holes and three bolts:
Now that we have everything clean, it's easy to see what we are dealing with.
I've realised that as the flywheels are 8" in diameter there is no way I can contemplate truing them in my lathe, so they will have to be sent away for repair. This is going to be expensive.