Secondary Shaft BGM PRO for Vespa Largeframe PX, Rally, T5, Cosa, LML (2-Stroke)

Modern cylinders like Malossi MHR, Quattrini M244 or Pinasco 251 have raised the performance and torque level of Vespa Largeframe engines to a completely new level.
The used transmission components must be correspondingly stable.

MATERIAL QUALITY
The BGM PRO secondary shafts are made of high-quality 21NiCrMo2 (1.6523) case-hardening steel, the surface of which is finally hardened to 62HRC. The high core strength of the material (900N/mm²) enables maximum load transfer (high engine torque), and the very good toughness (ductility) provides high resistance to peak loads. The final hardening (heat treatment) hardens the surface to a depth of 0.6-0.8mm, resulting in maximum wear protection.

• MATERIAL: 21NiCrMo2 (1.6523)

• HARDNESS: 62HRC

• GEAR RATIOS 1-4:

• BGM6504: 12-13-17-21 (Standard Ratio)

• BGM6505: 12-13-16-19 (shorter third, extra short fourth gear)

• BGM6506: 12-13-17-20 (shorter fourth gear)

MAXIMUM STABILITY THANKS TO CORRECT TRANSMISSION RATIO
The ratio of the secondary shaft, in addition to a perfect adaptation of the transmission to the engine characteristics, has another important aspect.
The fewer teeth a gear pair has with the same axle distance, the more stable it is (the teeth become wider).
For this reason, a motor with high torque, for example, should not use a 'short' fourth gear with 36 teeth (original only with 125cc!). Here the tooth flanks are narrower than with the 35-tooth wheel of the 200ccm models.

BGM6505: 12-13-16-19 (shorter third, extra short fourth gear)
Another expansion stage is the secondary shaft with 12-13-16-19 teeth. Here, the third gear is also one tooth shorter, and the fourth gear is already two teeth 'shorter'. This means that the gear jumps from 2-3 and 3-4 are significantly shorter than with the factory ratio from Piaggio. This ratio is ideal when a very long primary reduction (e.g. BGM 25/62) is to be used in a high-torque engine or the engine is very high-revving and requires a short gear stage to always stay in the engine's power band.

BGM6506: 12-13-17-20 (shorter fourth gear)
To nevertheless achieve a better gear engagement between the third and fourth gear with maximum stability at the same time, we recommend using the secondary shaft with 12-13-17-20 ratio. Here, the secondary shaft has one tooth less for the fourth gear (20 teeth instead of 21 teeth = more stable) and can therefore be combined with the original fourth gear of the 200ccm models with 35 teeth (= more stable). As a result, you have a fourth gear that is again slightly shorter geared than with the 21/36 pairing (approx. 2-3km/h) while simultaneously increasing load capacity. This secondary shaft is therefore ideal for engines with a lot of torque and a linear power curve. The engine can then be sufficiently long geared on the primary side, while the gear jump from three to four remains exactly right.

ACCESSORIES
As an ideal combination for a powerful engine, we recommend the perfectly matched clutch and primary parts from BGM PRO. For powerful engines, we exclusively recommend the use of straight-cut clutch and primary drives. These are structurally designed for the high loads and are not louder than the helical gear parts due to their careful manufacturing. Likewise, the springs of the primary internal shock absorbers are adapted to the high torques. The stiffer springs prevent the shock absorber from 'blocking', effectively keeping peak loads away from the transmission. The BGM PRO secondary shafts are designed for use with BGM PRO or original Piaggio gears. The BGM PRO secondary shafts are designed for use with BGM PRO or original Piaggio gears.

About the Manufacturer BGM

BGM is a leading brand for high-quality spare parts and accessories for scooters, motorcycles and classic Vespa models, which stands for quality, precision and innovation. With a uncompromising “Made in Germany” philosophy, BGM develops durable products in collaboration with leading engineers and under strict quality controls. Whether restoring vintage vehicles or tuning modern scooters – BGM is the first choice for demanding drivers. Thanks to first-class workmanship and a wide range, BGM offers ideal solutions for performance, everyday use and individuality.