VMC 177cc Stelvio with 57mm stroke and 63mm bore

Traditionally there have always been a vast selection of tuning cylinders available for the largeframe Vespa models fitted with the smallblock original 125-150cc motors. Alongside the larger, more well-known manufacturers, the market is also complemented with the added spice provided by the smaller producers.

The VMC is an economic alternative amongst the cylinders available with 177cc. It is constructed using aluminium and is equipped with a plated bore lining. It possesses four transfer ports and three boost ports combined with a single exhaust port.

It shares its 63mm bore diameter with most of the racing cylinders available in its class and is intended primarily for combination with a 57mm stroke crankshaft, although 60mm stroke types can also be used. This conversion requires the extra 1.5mm, that the piston protrudes from the cylinder to be compensated for with the use of gaskets or spacers at either the base or head of the cylinder. The cylinder has 114° blow down timing and 171° exhaust timing when delivered.

The cylinder head is CNC machined, has an 'O' ring gasket, is also centralised and is attached using eight bolts. The recommended squish clearance is 1mm (+/- 0.1mm). Gaskets of varied thickness are included to facilitate this. The exhaust manifold for the VMC cylinder is made of steel, is also equipped with an 'O' ring gasket and is attached using four bolts.

The manufacturers recommend:

• Spark plug: NGK B9ES; BOSCH W3CC
• Ignition point: 19° before TDC
• Main jet: 125-130