Re: what did you do to your motorized bicycle today?
That would work just as well... I think boring out the center hole first then slicing off the needed thickness would be the easiest way. The spacer needed in this case is more like a precicely sized ring than a washer because we need to make sure we don't block off the bearings from getting the proper amount of lube. Now if I can find a piece of silicon bronze bar stock that's about 1" diameter.... finding it isn't too hard but getting somebody to sell just a small piece of it like maybe 3" or so may be...
Brass or other types of bronze would work just fine too I'm sure, even annaluminum alloy like 6061 or 7075 T6 would work and hold it's shape for the life of the engine.