The sleeve valve is the only alternative to the poppet valve that has enjoyed significant commercial success.  It is difficult to make due to the fine tolerances required, but has shown itself to last much longer than equivalent poppet-valve engines.  It is also capable of running a compression number higher, for a specific grade of fuel. Key points to note are that the sleeve moves with an elliptical motion, and is moving relative to the piston at all times.  This is important because bore wear is significantly reduced.  There are, or were, heat transfer problems with the sleeves, due to the gap between the sleeve and the engine cylinder it ran in. There is no provision or need for adjustment of the sleeve once it is installed.  This is also true for the rotary valves shown on these pages.