S p e c s: VMA1M Motor

1965 - 1967
casing mouth: 2 transfer ports
induction: disc valve
bore: 55 mm
stroke: 51 mm
cubic capacity: 121.1 cc
compression ratio: 8.2: 1
bhp at rpm: 5.6 @ 5500
con rod length:97mm
piston compression height: 36mm
piston type: domed
small end diameter:19mm
big end diameter:20mm

flywheel side bearing: N204ECP (2 piece)
flywheel side bearing: 6024 (1 piece)
drive side bearing: 6303
clutch bearing: 16005
input shaft bearing: (flywheel side): 6200
output shaft bearing (flywheel side):
rear wheel bearing: 6204

flywheel side oil seal: 19x32x7
drive side oil seal: 22.7x47x7/7.5
rear hub oil seal: 27x37x7

Vespa 125 Links:
VMA2T overview
VMA2T electrical page
Engine Work

Casings: The crankcase mouth is 61mm to accept all kits. The 19mm intake manifold is attached with only two studs compared to 3 studs on later PK models

Bearings: Early motors had one piece bearings on both sides of the crank which are a pain when splitting the casings. The one piece flywheel side bearing can be replaced with a two piece to make splitting the casings easier in the future. Use an SKF N204ECP for the conversion

Cranks: Any smallframe crank can be installed in this engine. Popular changes are to install a PKXL or PK125ETS crank which allows use of many different flywheels. Flywheel side bearings and seals will differ for these conversions.

Standard barrel: The original Primavera barrel has only two opposing ports in the barrel. The later Primavera ET3 barrel & piston has three ports and can be used on earlier models as the third port is completely contained within the barrel casting (i.e. no casing modifications are necessary.. Both the barrel and the piston will have to be replaced for this conversion.

Kits: Any small frame kit can be used on this motor.

Ignition: The original 6V points can be replaced with a 12V electronic set up off a later Primavera ET3 or any of the PK range systems. The flywheel and stator off an ET3 bolt right on, but many PK flywheels use a different taper. Check here for a guide to smallframe cranks.

Gearbox: Any smallframe gearbox will fit in the casings but almost all the parts will have to be replaced.