Sir Sam wrote:
The manual KJs do have a dual mass flywheel.
If anyone ever gets inspired to create a single mass flywheel from a steel billet. Before you chuck it into the lathe, put your billet into an oven set to 500F (360C) and let it bake for one hour for every inch (25.4mm) of thickness, you can go longer and not do any harm but it is not needed. Then turn off the oven over night and let it cool until you can comfortably remove it with your bare hands. This way the steel will normalize and not distort when you machine it into the desired shape to fit and function. When you are all done machining and it fits great, slip on the starter gear you harvest off the dual mass flywheel and send it off to the racing machine shop to have it balanced. Don't let on that it is not for your track toy, they don't need to know and will do their best so that the flywheel is balanced to 10,000 RPM.
Other options are cast steel or nodular iron casting from a local foundry, but let it sit outside in the weather with a coat of oil or paint for a year so it can stress relieve. There are other options for stress relieving like chilling to absolute zero and bringing the temp back up to room temp, but last time I checked these people have their own Gulf-Streams parked out in back of their houses. There may be other stress reliving tricks but pouring Guinness or other fine Brew on the casting won't work! Even if it is body processed first.
One trick I have done before is to get a flywheel that is close to what I need, cut out the old hub where it goes onto the crank, have a very experienced welder TIG weld in a new hub blank, machine it to fit, tweak the other dimensions such as the pressure plate holes, starter ring gear, and pilot bearing, then take it to the race machine shop to have it balanced.