CNC-machined upgrade for spring-loaded Vespa small-frame primary drives. Reinforces the clutch basket and spring cover for high-performance, high-torque engines.
The BGM PRO Primary Repair Kit replaces the stock clutch basket and the thin cover plates of the spring-loaded Vespa small-frame primary drive with solid CNC-machined components. Manufactured from 42CrMo4 and subsequently nitrided, the set is designed to withstand the stresses of high-performance, high-torque engines.
The reinforced clutch basket holds the clutch plates, while the CNC-machined cover plate securely holds the shock-absorbing springs in the primary sprocket. This reinforces precisely those areas where stock baskets and cover plates often reach their limits in tuned engines.
BGM PRO CNC-machined 42CrMo4 nitrided Made in Germany For spring-loaded primary drives only
The primary drive connects the crankshaft to the clutch and transmission. In addition to pure power transmission, the integrated shock absorber performs an important function: Its springs dampen harsh load changes and reduce stress on the clutch, transmission, and gear teeth.
In stock primary drives, these springs are held in place by relatively thin metal plates. As engine power and torque increase, the stress on the springs, covers, and clutch basket grows significantly. The metal plates can deform, tear at the mounting points, or—in the worst-case scenario—break.
The BGM PRO Kit replaces these components with a solid, CNC-machined construction. This ensures that the shock absorber springs remain reliably guided even during severe load changes.
| Stock component | BGM PRO Version | Advantage |
|---|---|---|
| Clutch basket made of stock material | CNC clutch basket made of 42CrMo4 | Greater dimensional stability for high-performance engines |
| Thin cover plates made of sheet metal | Solid CNC-machined cover plate | Secure guidance and coverage of the shock absorber springs |
| Multi-part repair assembly | Two-piece BGM PRO system | Fewer individual parts and simplified assembly |
The clutch basket is manufactured from 42CrMo4. This heat-treated steel combines high strength with good toughness, making it suitable for dynamically loaded drive components.
In a high-performance small-frame engine, the tabs of the clutch linings act on the flanks of the cage during every acceleration and shifting operation. Soft or overly thin material can deform or be driven in by the linings during this process.
The solidly constructed BGM PRO basket provides a significantly more robust foundation for high-performance clutches and high engine torques.
The clutch basket and cover plate are nitrided. This process hardens the surface layer of the material without making the entire component brittle.
The hard surface reduces wear on the contact surfaces. Particularly at the guides for the clutch linings, it prevents the typical working-in of the lining tabs into the cage. At the same time, the tougher material core is preserved, which can absorb fluctuating and shock-like loads.
The cover plate seals off the shock absorber area and holds the springs in place in the primary sprocket. The stock system uses thin sheet metal plates for this purpose, which are among the weak points of the primary drive under high loads.
The CNC-machined BGM PRO cover plate is made of significantly more material and distributes the forces over a larger area. It prevents the springs from pushing through the cover or breaking off at the mounting points.
This preserves the function of the shock absorber. The springs can absorb harsh load changes without losing their secure guidance within the primary sprocket.
The current version of the BGM PRO primary kit consists of only two main CNC-machined components: the clutch basket and the cover plate. Compared to the earlier version with loose sleeves and two separate cover plates, this makes assembly much simpler.
A strategically placed recess in the clutch basket facilitates the replacement of the small clutch pinion. With the appropriate setup, the pinion can thus be replaced without having to remove the entire primary drive from the engine case.
This is particularly convenient when the primary drive ratio needs to be retrofitted to accommodate a modified engine design, a different exhaust system, or a new transmission ratio.
The BGM PRO Kit can be combined with the standard Vespa small-frame clutch types. These include the classic clutches of the V50, PV125, and ET3, as well as XL1 and XL2 versions.
The primary repair kit can be used with both standard shock absorber springs and reinforced BGM PRO springs.
The choice of springs depends on engine power, torque, vehicle weight, and intended use. Springs that are too stiff can reduce the damping effect, while springs that are too soft may bottom out prematurely or become overloaded in very high-performance engines.
For heavily tuned engines, we therefore recommend a spring configuration tailored to the engine design.
The kit is intended exclusively for Vespa small-frame primary drives equipped with a spring-loaded shock absorber.
Many Vespa 50 engines come standard with a simple primary gear ratio without shock absorber springs. The BGM PRO Primary Repair Kit cannot be installed in this configuration.
However, if the 50-cm³ engine is converted to a spring-loaded primary drive, the BGM PRO kit can also be used there. Therefore, the decisive factor is not just the vehicle model, but the actual primary drive configuration installed.
For 50-cm³ models, the kit can only be used if a primary gear ratio with shock absorber springs is installed.
| Manufacturer | BGM PRO |
|---|---|
| Component | Clutch basket with primary repair kit |
| Design | Two-piece |
| Manufacturing | CNC-milled |
| Material | 42CrMo4 |
| Surface treatment | nitrided |
| Manufacturing | Germany |
| Application | Vespa Small Frame Primary Gear Ratios with Shock Absorber Springs |
| Shock absorber springs | Suitable for stock springs and reinforced BGM PRO springs |
| Clutch Types | V50/PV/ET3, XL1, and XL2 |
| Special Feature | Recess for replacing the clutch pinion |
| Not compatible | Springless primary gear ratios on the 50-cm³ models |
The BGM PRO Primary Repair Kit reinforces the critical components of a spring-loaded Vespa small-frame primary drive. The CNC-machined clutch basket made of 42CrMo4 provides a sturdy mount for the clutch plates, while the solid cover plate reliably holds the shock absorber springs in place within the primary sprocket.
Nitrided surfaces reduce wear, the two-piece design simplifies installation, and the recess in the basket facilitates future modifications to the clutch pinion. This makes the kit particularly suitable for high-performance street, touring, and sport engines, as well as a complement to the BGM PRO Superstrong clutch.
DE | €
