Marcellina Split Single Engine
The designer was named Marcellina, an Italian. These
engines were described as a "Marcellina split single". Exhaust was handled in
the ports in the front cylinder, intake and transfer was done in the rear
cylinder, combustion chamber is a pair of semi-round chambers with a narrow
trench between them, uses a single spark plug. Both pistons were phased to not
run equally up/down the cylinders together, one always led the other. One rod
was run off the crankpin, the other off a boss/pin above the crankpin, off the
first rod.
Puch (Austria) made them in large numbers, also sold as Sears Allstate here in
the U.S., and there were a 125SV, 175SV and SVS, and a 250SV. SV, single carb,
SVS, two carbs, one on each side of the engine, with progressive operation. On
the SVS's, one was the primary carb (on the left side of the cylinder), the
other a secondary (on the right side of the cylinder) that came in at 1/3rd
throttle opening settings. SVS second carb had no float, used a hose from the
left float bowl to set the liquid level in it.
125/175 were premix, 250 had oil injection. Premix bikes had an oil cup on the
underside of the gas cap, one cupful for each gallon of fuel.
I have a 175SVS and a 250SV, and Kent Riches at AirTech likes and has a few
250's.