V5A3M is a Vespa engine prefix/VIN code.

V5A3M is engine VIN number for 50cc engine used in 50s, 50 Elestart vespa models made through years 1963 - 1972.
P.S. This engine VIN number is for the engine block/casing and it doesn't mean that over the years and even accross the models there isn't slight modifications of this engine parts, their sizes or even internals.

V5A3M engine specification

50s (1963 - 1966) V5A3M engine specs

engine: single cylinder, air cooled 2-stroke induction: disc valve bore: 38.4 mm stroke: 43 mm cubic capacity: 49.77 cc compression ratio: 7.2: 1 bhp at rpm: 2.6 @ 5800 lubrication: 2% oil transmission: 4 speed constant mesh primary drive: 14/69 1st gear: 1: 29.54 2nd gear: 1: 17.74 3rd gear: 1: 11.50 4th gear: 1: 8.15 clutch: wet - multiplate carburetor: Dell'Orto main jet: slow running jet: diffuser: main air bleed: starter jet: ignition: contact breaker & coil ignition timing: 19 degrees BTDC breaker gap: 0.3 - 0.5 mm voltage: 6 volt wheels: 10" tires:3.00 x 10 max speed: 30 mph total dry weight: 161 lbs

50 Elestart (1969 - 1972) V5A3M engine specs

engine: single cylinder, air cooled 2-stroke induction: disc valve bore: 38.4 mm stroke: 43 mm cubic capacity: 49.77 cc bhp at rpm: lubrication: 2% oil transmission: 3 speed constant mesh 1st gear: 1: 25.12 2nd gear: 1: 14.13 3rd gear: 1: 8.94 clutch: wet - multiplate carburetor: Dell'Orto main jet: slow running jet: diffuser: main air bleed: starter jet: ignition: contact breaker & coil ignition timing: 19 degrees BTDC breaker gap: 0.3 - 0.5 mm voltage: 12 volt wheels: 9" tires: 2.75 x 9"

50s 1963-196650s
50 Elestart 1969-197250 Elestart