Primary Driven Gear 67 teeth,
input shaft, for Vespa 125 VNB
/150 GS VS5M
The gear cog attached to the clutch together with the primary driven gear make up the primary gear ratio of the motor of your VESPA. The primary driven gear is solidly riveted to the rest of the input shaft assembly and is so in constant direct contact with the output shaft assembly. The primary gear ratio of your motor is determined by the amount of teeth on either the clutch gear cog or the primary driven gear cog. The more power available, the higher the gear ratio should be so that the extra performance can be more effectively realised as real top end speed.
The primary driven gear cogs with 67 and 68 teeth are compatible with clutch gear cogs that have 20, 21 or 22 teeth. The primary driven gear cog with 65 teeth is compatible with the clutch gear cogs with the 21, 22 and 23 teeth of the clutch basket model with an outer diameter of 115mm. In combination with different sized output shaft gear cogs your gearbox ratio can be exactly trimmed to the needs of your particular motor setup.
Conclusion: Changing the primary gear ratio of your motor affects the effective gear ratio of all your gears and should always be considered when extra available power needs to be turned into extra top end speed.
SIP-TIP: Do not forget to order a suitable primary drive repair kit and new gearbox oil!
SIP Community user ‚charly‘ on Art.-Nr. 11272000: „Cool! Very good item.”
OEM Numbers (for the purpose of comparison)