The engine casing
The engine housing of the 306 cc BFA engine is based on a newly developed casting mould. Shaft distances and basic construction of the power transmission remain the same. They correspond to the original from Piaggio. BFA has created a lot of space around this basic shape. Space for a stronger crankshaft with more stroke, for the cylinder with the 78 bore and the widely shaped overflow channels, and space for greater wall thickness and bracing. The distance between the cylinder studs is 100x100 mm. The massive mounting for the auxiliary shaft stands out particularly positively. The inlet into the engine housing is located directly across under the cylinder base, goes over both housing halves and offers 70mm of space for the diaphragm. Both crankshaft bearings have an outer diameter of 62 mm. On the clutch side the crankshaft is guided by a cylindrical roller bearing, the fixed bearing is located under the ignition. The oil seals are 25x35x7 and 25x40x7. Intake manifold and diaphragm are not included. The kit from BFA comes with a large 4 flap diaphragm known from Quattrini and DEA cylinders. The short, cast intake manifold directs the mixture via a buffer into the housing. Inner diameter is 40 mm, port diameter 45mm.
The core of the BFA 306 engine is the completely redesigned cylinder. It generates its unusually large displacement from a stroke of 64 mm and a bore of 78 mm. The piston is a flat top piston with a piston ring. The cylinder head is screwed 8 times, the spark plug is centrally located and sealed by an O-ring. The gas exchange takes place via 5 overflows and a 3-part exhaust. The exhaust flange is made of steel and is fixed to the cylinder with 4 screws. The outer connection diameter is 50mm. The cylinder stud bolts are not continuous, the cylinder is screwed to the base. This gave the designers unlimited space when designing the ducts.
With a width of 54.4 mm and a diameter of 102 mm, the crankshaft of the BFA Kit has particularly strong dimensions. The polished forged connecting rod is 135 mm long. The most striking feature of the crankshaft is the clutch stub. Here, the clutch is not simply secured against rotation with a wedge, it is pushed onto a stable toothing. On the alternator side, fan wheels with original cones can be fitted.
The clutch, which BFA has designed for the 306 cc engine, is connected to the BFA crankshaft via a splined connection. The basis is the PX clutch from the BFA programme. The functional principle of the Vespa Largeframe clutch has been reversed. This is intended to connect fewer masses rigidly to the crankshaft and to have the effect of improving the grinding-in behaviour of the clutch, making the clutch less "jerky" when starting off and generally easier to operate. The primary pinion is specially made for this clutch. This not only ensures that BFA has a strong and robust solution, but the flat design of the pinion also saves a lot of installation space. This is a decisive prerequisite for accommodating 5 lining discs in the clutch. The clutch pinion is connected to the CNC-milled, outer aluminium basket via 12 screws. The inner shaft is supported by a needle bearing instead of the original bronze bush. The pressure plate is also equipped with a bearing, which is fitted into an aluminium rotating part. All friction discs and cover plates of the clutch pack are also made of aluminium. In the lowest plate, similar to a smallframe clutch, there are 6 springs, which can be supplemented by 6 small springs placed in their centre. A straight-toothed primary transmission is included in the delivery. Also two screws with which the clutch can be compressed and which allow the pads to be changed in the installed condition. The whole thing fits under the original clutch cover of the PX 200.
The exhaust of the BFA 306 engine, like the other parts, is specially designed for this engine. This not only means that it fits on the exhaust flange of the cylinder, it has been calculated for displacement, timing and channel cross-sections and thus produces a powerful and harmonious power curve.