I'd do it myself. Make sue you've got the right size piston and pistonsprings to go with your cylinder. Be very carefull not to drop anything into the carter, wrap a piece of cloth around the driveshaft to block the hole in the carter. And make sure NOT to scratch the piston or the inside of the cylinder, and be carefull not to break the pistonsprings. The rest schould be done just like it says in the manual. Also you shouldn't use old gaskets, always use new gaskets and make sure to tighten the cylinderhead down equally across.