I recently sold 4 X-11's all with the blue head and I kept one for myself. I also have an X-11 without the blue head (plain aluminum) but am in need of parts for it . water got to it and went undetected til rust set in but would like to restore it with new piston sleeve crank and I'll get a Boca bearing when I've gather up all the other parts. the X-11 was .11 cubic inches and for a small engine mine ran great with excellent idle,, midrange and full out.