O.K. - It was a long while ago!! As for Sleeve Valves these take the form of an extra liner between the cylinder and piston. They have slots cut out which line up with ports in the cylinder when the sleeve is rotated. I have read horror stories of the extremely complex drive mechanism and the difficulty of setting it all up... I assume the varying expansion rates causes the the high oil consumption, and start up smoke. Mind you all radials are prone to this. A local pilot bought an AN2 some years back and it was not a good idea to stand downwind when he fired the engine up!