PIAGGIO revolutionized the world of large frame motor transmissions with the introduction of the COSA II clutch. All the existing large frame clutch problems were solved almost overnight.
Since around 1995 the COSA II clutch has been used in all VESPA PX EFL/'98/MY /'11 and of course, the COSA II models build by PIAGGIO. It comes complete with 4 friction plates, 8 springs and a sturdy clutch basket design. Due to the higher pressure created by the increased number of springs and the increased frictional surface area power can be transmitted more effectively between the crankshaft and the gearbox. Precision laser-cut clutch plates prevent any problems with snagging clutches. No jerking, no slipping, an optimal release point and all that combined with a light, easy clutch lever action, even when using a stronger set of springs.
The gear cogs for the COSA II clutch are available with 20, 21, 22 and 23 teeth. The cogs with 20 or 22 teeth fit into 125-150cc motors and the 21 or 23 toothed cogs into the 200cc motors without having to also replace the primary driven gear cog. If, on the other hand, another primary gear cog or the DRT clutch gear cogs are used, more transmission ratios are possible. All VESPA large frame models since the VNA/VNB range up till 1994 can be fitted with the COSA II clutch. With these 125-150cc models the existing clutch cover must either be modified due to the largest size of the COSA II clutch conversion, or replaced with the clutch cover from the 200cc motor with a suitable pressure plate.
The traditional Italian manufacturer NEWFREN has a version of the COSA II clutch available with a reinforcement ring welded around the outside diameter of the basket and also springs, stronger than the original items. This 'ringed' version should only be included in motors tuned up to around 15 PS. For all you original VESPA fans we also have the original PIAGGIO version in stock.
Helpful Hint: Regrettably the production quality standards of both manufacturers of this clutch system was not always consistent with the high quality we have come to expect from PIAGGIO & CO. We recommend therefore that these clutches only be used, in their standard form at least, in original motor setups. When a reinforcement ring is included, mildly tuned motors can also benefit from this clutch system. If however, the comfort that this clutch system offers cannot be done without - even in a highly tuned machine – the use of another more suitable clutch basket produced by either ourselves, MMW or Scooter & Services is strongly recommended. Attention: Not compatible with PINASCO clutch bush Part.-No. 59366000!
Conclusion: Combined with a suitable clutch basket the COSA II clutch remains the absolute recommendation for every VESPA large frame motor.
SIP-TIP: When the clutch assembly is completely assembled, prior to mounting on the crankshaft, the 'neck' part of the clutch base plate that connects with the crankshaft itself should protrude 0,5-0,7 mm further towards the rest of the engine than the clutch gear cog to ensure the clutch operates correctly. The somewhat lax manufacturing tolerances of various clutch components can result in this gap being reduced causing the spacer washer to come into contact with the primary drive gear cog, so preventing clutch plate separation. Should you encounter this problem while mounting your clutch we recommend slight modification to your primary drive gear cog with a slight chamfering to a ratio of 2:10 or the use of a suitably modified spacer available at our shop (Art.-Nr.69821000). For inclusion in the more powerful tuning setups the use of a stronger clutch basket is necessary!
SIP community user “Klose” on Art.-Nr.28865000: “Recommendable! Fits well and works even better!”
SIP community user ‚CSHCSH‘ (über Art.nr.28865000): „It's extremely easy to shift without too much pressure, while giving excellent mid and high end.“