Benelli 4M 4MS 4M65

1969 Benelli Parts Catalog Dynamo Compact 50cc Dynamo Trail 50cc Dynamo Woodsbike 50cc

1968-69 Dynamo

Benelli models with 4M, 4MS, 4M65 engines 1965-77

49 or 59cc vertical cylinder 4-speed foot-shift, manual clutch.

1960's Benelli 50cc 4-speed foot shift, "mild" version with Dellorto SHA carb

Left 4M, right 4MS, 16 intake

1969 Benelli Dynamo Trail 50 engine

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 engine parts

4M and 4MS partial parts list:

00#  price 0 1970# 00000 description        specs
002  $0.20 ‌MU332head washer ∅6

3  $0.40 ‌MU280 head & ex. nut M6
none   ‌G7007 cylinder stud M6 x ?
011  $12.0G7010 head gasket ∅41
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  $65.0G7346/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




1972 Benelli Dynamo 65cc Parts Manual

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. 


1969-75+ Benelli 65cc 4-speed engine

Benelli 4M65 engine