In the engines of smallframe VESPA models the power created by the motor is transmitted by the primary drive cog, located on the crankshaft, to the primary driven cog located on the outer edge of the clutch basket. The clutch assembly is located on the input shaft of the motor itself which transmits the power further through the output shaft to the rear wheel. The more power the motor puts out, the sooner your clutch needs replacement.
The original primary drive has diagonally cut (syncromesh) connecting teeth and are delivered including the primary drive cog and clutch basket with the corresponding cog around the outside. If a clutch basket from another model of small frame VESPA is used this can make the overall gear ratio of the motor either taller or shorter. If the model you are looking for is not listed it is only available with straight cut gear cog teeth. Through changing the size, or number of teeth, on the primary drive you can vary the overall gear ratio of your motor.
Due to the fact that they have differing outer diameters these cogs are not automatically compatible with all other sizes of cogs available. The best solution is offered in the form of the DRT range of engine gear cogs...
Conclusion: The primary drive assembly should be replaced during every major service of your gear box.
SIP-TIP: Do not forget to order a new fixing nut for the input shaft, a safety washer, new bearing and fresh gearbox oil for safe and enduring use of your motor.
14/69 and 15/69 primary transmissions were installed on the original 3-speed smallframes. Their production is long since discontinued, however. That isn?t such a shame as they had an extremely unfavourable transmission ratio. On the Vespa 50 Special this was different, however. The 16/68 primary drive was fitted to this model. With a ratio of 4.25 it is the best primary transmission for an original or tuned 50cc Vespa. It is also perfect when installed on the APE 50 series. Its production is also long since discontinued, however. As it is the first choice for all 50cc restoration jobs SIP has decided to get DRT to reissue this primary transmission again.
The reissuing of this component means the 15/68 teeth and 17/68 teeth slanted teeth transmissions are now possible again. This means all the areas of slightly tuned 50-75cc smallframes are now covered.
SIP-TIP: the DRT 17 teeth gear wheel means the transmission can be extended elegantly.
