1968-69 Dynamo
5. Benelli models with 4M, 4MS, 4M65 engines 1965-77
49 or 59cc vertical cylinder 4-speed foot-shift, manual clutch.
Left 4M, right 4MS, ∅16 intake
4MS engine
4M engine: The 4M has a mild cylinder, with shorter and narrower ports, a 12mm ID intake, and a smaller 12mm Dellorto SHA 14/12 side-draft carburetor.
The 4M engine was on the 1968-69 Benelli Dynamo Compact. M means marce, Italian for “march”, or in the motorcycle industry “foot-shift”.
4MS engine: The 4MS has a “sport” cylinder, with taller and wider ports, a 16mm ID intake, and a larger 16mm Dellorto UA16S down-draft carburetor. Horsepower 4.5 at 7800 rpm. This is the version shown in the parts illustration.
The 4MS engine was on the 1965-68 Benelli Fireball and Fireball Trail, and 1969 Dynamo Trail and Super Mini.
Benelli 4M and 4MS engines
1969-75 Dynamo
4M65 engine: Since 1970 the 4M and 4MS 49cc engine size was increased to an advertised 65cc on the 4M65. But the actually size was 59.3cc. Bore and stroke were 44 x 39 mm. That was dishonesty in labeling, motivated by “bigger is better” thinking.
The Benelli 4M65 engine is on 1971-73 Mini Enduro, 1970-72 Cougar, 1970-71 Dynamo Compact, Dynamo Trail (Scrambler), Woodsbike, 1972-73 Compact II, Dynamo II, Woods II, 1974-75 Dynamo Trail, 1976-77 Dynamo. It has large square head, larger piston, Dellorto ME15BS carburetor.
Benelli 4M65 engine