The cylinder and crankcase are one casting. You will need to strip the engine literally to the last nut and bolt, and rebuild the engine into a new block casting. You will need to replace the piston also - your old one won't match the new cylinder.
It's unlikely to be cost effective unless you can get the parts at trade prices.
phil_saunders(a)bigfoot.com
Phil Saunders, November 2009
