For those of us brought up fooling around with auto engines the sleeve valve can be a bit of an enigma and what is interesting is how this apparent complexity can turn out, when done right, to be so reliable. It must be something to do with the lack of shock in the action and the relatively low acceleration of the parts.
It also has other advantages besides just the sheer size of the ports it allows, for instance the ability to renovate by just pulling and replacing the sleeve. Granted the high friction area between the sleeve and the block must make the power requirement for starting a bit of a nightmare.
Seems a bit surprising there is not at least one eccentric auto manufacturer out there building a sleeve valve engine instead of the four or even five valves per pot jobs that are around now.