An Output Shaft for Vespa largeframe models, including integrated gear cog positioning.
The sometimes imprecise positioning of the cruciform within the Vespa largeframe engines output shaft is considered as one of its major weak points. To ensure the cruciform facilitates an effective transmission of power between the chosen gear cog and the shaft itself, precise positioning is essential. If the cruciform is not exactly aligned with the internal openings of the gear cog, the gear cannot be properly engaged and will disengage or find a false neutral. This is potentially dangerous in traffic and can also lead to expensive gearbox damage.
- Exact positioning of the cruciform within the output shaft.
- Compatible with PX Lusso gearbox components.
- Relatively simple mounting, mechanism is pre-assembled.
On Vespa largeframe engines the positioning of the cruciform within the output shaft is determined by the external selector box. As this component is not solidly fixed to the output shaft, there are many peripheral components involved and each adds to the many variables and manufacturing tolerances that have a negative influence on correct alignment of the cruciform. In addition there is also inevitable mechanical play between the selector arm and the selector rod and over time these parts wear making the imprecision even worse. These factors combined do not make the setting up of a PX largeframe engines drive-train any easier, especially when tuned.
The solution from CRIMAZ
Christian Mazelli took on this issue and, as usual, came up with an excellent solution! His chosen method is intended to provide a more solid, direct connection within the output shaft, similar to the system used with Vespa smallframe and Lambretta engines. A spindle equipped with machined slots, protrudes through the cruciform as an extension of the selector rod within the confines of the shaft. There are three sprung tensioned ball-bearings located in the shaft that engage with the slotted spindle and effectively anchor the cruciform in the correct position to meet the chosen gear cog precisely.
A new method of gear selection restraint, all located conveniently within the output shaft! This innovation also helps make this conversion shaft compatible with almost all peripheral PX Lusso gearbox components. The exception is provided by the fact that the diameter of the primary drive cog should not exceed 115mm as larger items could come into contact with the slightly thicker CRIMAZ shaft construction. This remains entirely acceptable though, as primary drive cogs with 65 teeth or less are recommended for use with this output shaft and they are small enough to fit anyway. The individual cog positioning enabled by this shaft is set up for PX Lusso gear cogs.
To ensure the function of the CRIMAZ positioning mechanism is not obstructed the original selection mechanism requires deactivation by removing the pin and spring that normally engages with the external selector disc.
This output shaft upgrade kit includes all necessary components to facilitate its use and also comes pre-assembled
- Output shaft.
- Selector rod.
- Cruciform.
- Circlips.
- Spacers.
- Selection mechanism.
Conclusion: An innovative solution that will extend the effective life of many PX Lusso gearboxes!
The best set up – our SIP–TIP:
- Complementary CRIMAZ input shaft with a 12, 13, 17 & 20 toothed gear set (#25270870).
- Do not forget to order the matching primary drive cogs for this set up. A 23/64 toothed combination is ideal for most tuned largeframe engines, a straight toothed version is not only better at transmitting increased power – but also eliminates damaging axial forces along the shaft (#67167210).
- Our SIP-BFA clutches (#78245900 or #93406600) complement these high-end gearbox components perfectly.
