My bet is a rotary valve intake. Most model engines are not piston port timed alone. The crankshhaft is hollow and a port aligns with the carb opening before BDC. This fills the crankcase on the upstroke allowing some compression of the charge on the downstroke after the crankshaft opening closes off the carb port.
Because of the way a twin fills the crankcase as both pistons rise, the charge could go to the first piston to open it's intake port causing a rich/lean condition beteen the two cylinders on that v section (if crankcase charged induction was used).
My bet is that the geared 1/2 to 1 shaft is an intake port timing device. The engine is a blend of two stroke and four stroke technology. It is hard to understand why they don't run the valve shaft at one to one as a 1/2 to one means that one full revolution will be used for nothing more than to make a piston go up and down. The shaft valve may help keep the charges seperate so both sides see equal burn, but this engine really needs a blower like a detroit two stroke desiel in design.  |