Discouraged by the fact that Google only comes up with this very discussion, I nevertheless reckon that it's a generic term for an ......and that Turnomat Valve Rotator is a brand name for same (see below). Used in marine engines as well. (Strangely, I came across this word recently but not in a context that lead me to remember its meaning, unfortunately.) (And see the helical tech. site, below, for a good explanation of what it does.)