A sturdy, low-vibration Full Circle Crankshaft for the BFA crankcase on Vespa Largeframe models.
A two-stroke engine has the advantage of having only three moving parts: the Crankshaft, Conrod, and Piston. This makes the engine simple and lightweight. In a Vespa engine, however, these parts are critical. That is why BFA took a thoroughly consistent approach to the Crankshaft’s dimensions when designing its engine.
- Heavy-duty design for smooth engine operation thanks to mass between the crankshaft bearings
- Long, high-quality conrod with good lubrication of the bearings
- Highly stable thanks to a wide design and high-quality materials
- Toothed clutch stub for optimal connection to the Clutch
To withstand high engine power, a crankshaft must have sufficient material at key points. This is the only way to ensure it remains stable enough. For smooth operation, an engine also requires a certain amount of mass—as close as possible to the point where the forces that cause vibrations occur.
Ideally, the crankshaft provides this mass itself, especially in high-performance engines.
The crankshaft journals—impressive
With a width of 54.4 mm and a diameter of 102 mm, the Full Circle Crankshaft is exceptionally robustly dimensioned. The resulting dead space is extremely small. Depending on the version, the Shaft weighs 3.5 kg or more; a standard PX Shaft weighs about half that. This is sufficient mass to significantly improve engine smoothness and stability.
Despite the crankshaft’s size, this weight can only be achieved through additional tungsten inserts, which also ensure proper balancing. A sophisticated yet effective method for giving the crankshaft the right mass.
The Forged Connecting Rod—A Sight to Behold
BFA crankshafts use polished forged connecting rods that are 120 mm long for 187–225 ccm engines or 135 mm long for 306 ccm engines. Generous lubrication slots at both ends ensure optimal lubrication of the bearings.
The clutch stub—a new connection between the crankshaft and the Clutch
One of the most interesting innovations is the clutch stub. It is available in two versions: conventional for 187–225 ccm and with teeth.
The gear teeth provide a significantly more robust connection between the Clutch and the Crankshaft. This requires matching toothed SIP BFA Clutches. The half-moon wedge is no longer needed. Clutches that strip off the stub or can no longer be removed are now a thing of the past.
The clutch is fitted with a special fine-threaded collar nut.
Technical features at a glance:
- Full Circle Crankshaft with 102 mm diameter crank webs, weighing 3.5 kg, and 54.4 mm wide.
- Stroke: 60 mm, 187–225 ccm, or 64 mm, 306 ccm
- Balanced with tungsten inserts
- Polished forged connecting rod: 120 mm, 187–225 ccm, or 135 mm, 306 ccm
- Serrated or standard clutch stub
- Includes Gudgeon Pin Bearing, clutch wedge for conventional design, and clutch nut
Note: Pay attention to the bearing positions during installation. The BFA casing has its own bearings, with the fixed bearing located in the smaller half of the engine block.
Conclusion: The perfect high-end Crankshaft and the technical centerpiece for BFA’s high-end Crankcase.
The best setup—our SIP TIP!:
- SIP BFA crankcase is absolutely required
- Crankshaft bearings, Part No.No. 90056100/90056200 and Oil Seals, Part No. 91033700/91033800 —don’t forget to order them; also order the Woodruff Key and PX pole wheel nuts
- The crankshaft can be gently pulled inusing the tool.
