S p e c s: V9A1M motor

1963 - 1984
casing mouth: 2 transfer ports
induction: disc valve
bore: 47 mm
stroke: 51 mm
cubic capacity: 88.5 cc
compression ration: 7.2: 1
bhp at rpm: 3.1 @ 5200
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 90 links:
Vespa 90 Overview
Electrical Diagrams
Parts Book
Owner's Manual
Engine Work

Casings: The crankcase mouth on this model was enlarged in 1966 to 61mm - an identical size as larger small frame motors like the 100 and Primavera. From 1963 to 1965 the crankcase mouth is only 56mm and the piston is different. See "kits" below for limitations because of this. The 16mm 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

Crank: The crank is the same as the 100 and Primavera models up to the Primavera ET3. 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.

Piston: On pre 1966 engines the pistons have a different wrist pin set up using a 14mm pin and only a bronze bushing aat the small end. Post 1966 engines have a 15mm wrist pin and a caged roller bearing small end (see pic) .

Standard barrel: The original 90 barrel has only two opposing ports in the barrel. The later 100 Sport or 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: Larger bore kits from Malossi and Polini (and others) can only fit on post 1966 engines without enlarging the mouth to allow the barrel spigot to fit.

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.