The gear cog attached to the clutch assembly drives the primary gear cog attached to the input shaft in the large frame VESPA motor. Through varying the size or number of teeth on this cog, you can change the primary gear ratio of your motor. Changing the clutch cog is the quickest and easiest way to change the overall gear ratio of your motor. The more teeth the clutch gear cog has, the higher the gearing.
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, the primary gear cog is also replaced, all clutch cogs can be used with both motor sizes. The primary driven gear cog in the 200cc motor with 65 teeth can be combined with 21 or 22 toothed cogs, along with the original item with 23 teeth. The most popular clutch gear conversion cog is the version with 22 teeth, so enabling an improved acceleration through the gears, without expensive tuning measures, especially between 3rd and 4th gears. For VESPA T5 motors equipped with the MALOSSI 172cc cylinder kit, a clutch gear cog with 21 or 22 teeth has proved suitable. If the primary driven gear with 65 teeth (originating from the 200cc motor) is used in a 125-150cc motor the clutch gear cog from the 200 can also be employed in the smaller motor.
DRT have also managed to close the gaps in the number of cog teeth available for the PIAGGIO COSA II clutch gears. DRT produces clutch gear cogs suitable for all sizes of primary driven gear. A noticeably quieter and durable drive train is the result. This also extends the overall life of your gearbox and therefore your motor and also improves the efficiency of the transmission, with more power reaching the rear wheel. The straight cut gear cog with 22 or 24 teeth are designed for use with the POLINI primary driven gear cog. The primary gear ratio of 2.67 resulting from the cog teeth ratio of 24 teeth on the clutch gear cog and 64 teeth on the primary driven gear is the tallest primary transmission ratio conversion available for the COSA II clutch apart from the Worb5 version naturally... The clutch gear cog with 23 teeth produced by DRT combines perfectly with the original PIAGGIO primary driven gears in 125-150cc motors with 67 toothed cogs and 68 toothed cogs respectively.
There are straight cut COSA II clutch cogs also by DRT available for the DRT primary drive cog with 62 teeth. With 23, 24 and 25 teeth many overall gear transmission ratios are possible in combination with the COSA II clutch.
Helpful hint: 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 larger size of the COSA II clutch conversion, or replaced with the clutch cover from the 200cc motor and a suitable pressure plate. For this reason they have also been included in the accompanying listings.
SIP-TIP: Do not forget to order a new clutch holding nut, safety washer, thrust plate and a pushrod. New clutch friction plates are also recommended when doing this job. With differing sizes of gear cogs on the input and output shafts even more experimentation with gear ratio is possible. Wider section tyres are also a popular way of raising the gearing of your motor.
SIP community user “FloMoBiMa” on Art.-Nr.28960700: “Harmonises ideally with the 177cc PINASCO cylinder.”