1968-69 Dynamo
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 ’65-68 Benelli Fireball, ’67-68 Fireball Trail, ’65-68 Riverside 450SS, and ’69 Dynamo Trail and Super Mini.
1965-68 Ward Riverside 450SS with Benelli 4MS engine
Benelli 4M and 4MS engine parts
4M and 4MS partial parts list:
00# price 0 1970# 00000 description specs
002 $0.20 MU332 head washer ∅6
003 $0.30 MU280 head & ex. nut M6
008 none B1348/2 spark plug = NGK BR6ES
009 none G7007 cylinder stud M6 x ?
011 $12.0 G7010 head gasket ∅41
013 none G7011/2 base gasket
035 $7.50 MU2265 drive seal 28-38-7
084 $00.0 MU7865 right crank seal
087 $45.0 G7346 piston bare dome top hi-comp use #91
089 $10.0 G7347 0 piston ring Std 40.0 x 1.5 GN
089 $22.0 G7347/2 piston ring 1os 40.2 x 1.5 GN
089 none G7347/4 piston ring 2os 40.4 x 1.5 GN
089 $16.0 G7347/6 piston ring 3os 40.6 x 1.5 GN
090 $8.00 G7115 piston pin ∅12 x ?
091 $65.0 G7346/C piston assy Std 40.0 x 17-12-18 GOL
091 N/A G7346/C2 piston assy 1os 40.2 x 17-12-18
091 N/A G7346/C4 piston assy 2os 40.4 x 17-12-18
091 N/A G7346/C6 piston assy 3os 40.6 x 17-12-18
100 N/A G7342 left crank seal 15-25-5
101 $70.0 G29 carburetor for 4M, Dellorto SHA 14/12 #58 jet
101 $00.0 G29 see Benelli FA section for parts list
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