I've owned a couple of SC500s over the years including the Champion framed version now raced by Edgar Phipps. The main problem with them is piston failure in the gudgeon pin area and an ignition curve that's all over the shop, similar to that of a TM400. I fitted DT400 outside flywheel ignition which transformed the bike and eventually sorted the piston failure/distortion problem with some minor welding buildup in that area. Edgar has been rooting around with them for years and has done a couple of interesting conversions. On one he fitted a five speed trans from an MX250 which involved removing the counter balancer which is on the transmission shaft where fifth geear would normally be. There is no noticable added vibration. On the other, in a bid to overcome the piston problems, he had a new sleeve made and has fitted a CR500 Honda piston. This engine is in my old Champion flat tracker and it is as fast as shit, and possesses none of the SC500 shortcomings. He uses both outside flywheel points ignitions and DT400 CDI setups.
Despite the horror stories, these old things are still pretty quick. If you've got the gonads to hold on to the bucking bronco handling, you can have a lot of fun on them.
