Shift cross bgm Pro SPORT BGM6501L

The bgm Pro Sport gearshift cross has been adapted to the increased requirements of today's engine concepts. The inner values are crucial to ensure that the gearshift cross provides reliable gear changes and riding enjoyment for a long time. The middle section (green) must ensure secure attachment to the shift bolt and be sufficiently flexible to prevent breakage at this point under high loads. This zone 1 is kept tough and elastic in connection with the material used and a hardness of approx. 45HRC. In zone 2 (orange), in which the shift cross runs in the main shaft, the shift cross must still have tough elastic properties but the surface must have a greater hardness in order to resist wear in the (very hard) main shaft at this point. The outer area (red) must be resistant to the impact load of the gears during the shifting process. These areas engage mechanically with the gears. High resistance to wear is required here. The hardening takes place at up to 60HRC. The new bgm Pro Sport gearshift clutch equipped in this way is a reliable companion for many kilometers with performance-oriented engine concepts. In order to check whether the gearshift crosses can withstand extreme demands and whether the middle section is sufficiently flexible, we have recorded a short test in the video. The test method used is rather pragmatic, but has already shown in various tests that gearshift crosses can also be too hard or too soft and deform significantly or even break.

The new bgm Pro Sport gearshift cross is available for PX 1982 to 2016 and PX / Rally / Sprint

PX 1982 to 2016PX / Rally / Sprint

How often should a gearshift cross be changed?

In an original PX125 with approx. 7.5 hp at the crankshaft and ridden in normal everyday use, a good sprocket can safely last the normal maintenance interval of approx. 20,000 km until the next engine overhaul without showing any significant loss of function. Of course, the wear looks completely different if a gearbox is operated with a Malossi MHR, 35 hp at the rear wheel and with a preference for mountainous country roads. In this case, the intervals until the next replacement of some engine components can be significantly shorter. Especially in the case of such a highly stressed component as the gear selector and the engine mounts, the intervals until a component needs to be replaced can be in the region of 10,000 to 15,000 km. The environment in which the gear selector operates is also a decisive factor for durability.

For example, it is essential to correctly calibrate the gears on the main shaft using the appropriate

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shoulder rings

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Shoulder rings transmission shims bgm PRO for Vespa and Lambretta

Click!If the axial play of the gear wheels on the main shaft is too large, the gear wheels on the main shaft can tilt and wobble and thus move the shift cross out of the respective gear wheel. Piaggio has specified a play of 0.1 mm as the installation dimension. According to the Piaggio workshop manual, the shoulder rings on an original engine should be replaced when the play reaches 0.55 mm. Based on our experience, we can only advise you to keep the play of the gears on the main shaft as close as possible to the installation dimension of 0.1mm. Heavily worn gears with clearly rounded end faces of the segments also lead to increased wear of a gearshift cross. On this crowned surface, the gearshift cross can no longer hold properly and jumps out of gear. So if you are carrying out an engine overhaul or want to change the gearshift cross, it is always important to look at all other components and replace them if in doubt.