BGM PRO Touring Evo rotary-valve crankshaft with 60 mm stroke and extra-long 128 mm connecting rod – for high-performance PX200 large-frame setups with Quattrini M244, VMC Explorer 244, and Polini 244.
The BGM PRO Touring Evo crankshaft (BGM031128G ) combines a 60 mm stroke with an exceptionally long 128 mm connecting rod. This makes it particularly suitable for cylinder designs where the cylinder geometry is intentionally shifted upward, and a long connecting rod provides additional flexibility regarding cylinder position, squish edge, and valve timing angles.
Typical candidates include the Quattrini M244, the VMC Explorer 244, and the new Polini 244. Especially with the Polini, the BGM crankshaft is an interesting alternative to Polini’s own 60/127 crankshaft: The BGM031128G features a conventional PX clutch stub, allowing the use of standard compatible PX clutch systems.
A second key design feature is the intake layout. The crankcase sidewall has a very deep intake shoulder in the area below the rotary valve intake. This provides a large free cross-sectional area early on when the rotary valve is open. This is particularly advantageous for high-performance engines, as it allows for a large effective intake cross-section to be achieved without necessarily requiring extremely long intake valve opening times.
BGM PRO Touring Evo 60 mm stroke 128 mm connecting rod Rotary valve Ø16 mm piston pin Quattrini M244 VMC Explorer 244 Polini 244 Deep intake shoulder
The 128-mm connecting rod length makes the BGM031128G particularly suitable for cylinders whose geometry is specifically designed for a long connecting rod.
| Cylinder | Compatibility with BGM031128G |
|---|---|
| Quattrini M244 | A very typical application for a 60-mm stroke and a long connecting rod; spacers allow for precise positioning of the cylinder. |
| VMC Explorer 244 | Suitable for long-connecting-rod 244-cm³ setups with a 60 mm stroke and variable cylinder position. |
| Polini 244 | Polini specifies 60/127 as standard. The BGM031128G offers a 60 mm stroke and 128 mm connecting rod; the additional 1 mm connecting rod length is accommodated via the cylinder position or appropriate spacers. |
Compared to the standard 110-mm PX200 connecting rod, the 128-mm connecting rod is exceptionally long. While the stroke remains unchanged at 60 mm, the geometric relationship between the crankshaft radius, connecting rod, and piston changes significantly.
Of particular importance to the engine builder is the additional freedom in cylinder positioning. With appropriate base spacers and, if necessary, head spacers, the cylinder can be positioned higher or lower. This alters the opening and closing points of the intake and exhaust valves.
This point is particularly interesting with the Polini 244: The cylinder is originally designed for a 127-mm connecting rod. The 128-mm connecting rod from the BGM031128G provides an additional millimeter of design leeway, which can be utilized or compensated for via the spacer configuration. This allows the final cylinder position to be more precisely tailored to the desired valve timing configuration.
In a rotary vane engine, it is not only the pure intake duration that determines how well the engine is filled. Equally important is the effective cross-sectional area that is open while the intake is open.
This is precisely where the layout of the BGM PRO shaft comes into play. In the area below the intake port, the crankshaft flange is deeply recessed. This deep intake shoulder creates ample free space right where the mixture flows from the intake manifold into the crankcase.
The result is a large usable intake cross-sectional area even at moderate rotary valve timing. This makes it possible to build a high-performance engine without necessarily having to close the intake very late.
On a typical PX200 engine case, the BGM PRO Touring Evo cam closes the rotary valve intake approximately 58° after TDC. The actual value depends on the engine case used and its intake port.
For a performance-oriented yet rideable street engine, an intake start of approximately 120° before TDC has proven effective as a starting point. The necessary machining is performed on the intake port of the engine block.
The combination of moderate opening duration and the deep intake shoulder of the crankshaft is a deliberate choice: It is not merely the maximum number of degrees of intake timing that generates flow, but rather a large effective cross-sectional area during the open phase.
The long connecting rod alters the geometry of the crankshaft assembly. With a 60 mm stroke, the crankshaft radius is 30 mm. The ratio of crankshaft radius to connecting rod length is approximately 0.234 for a 128 mm connecting rod; with a standard 110 mm connecting rod, it is approximately 0.273.
With the same crankshaft geometry, the longer connecting rod reduces the lateral angle of the connecting rod relative to the cylinder. This can reduce lateral forces on the piston and contributes to a mechanically favorable crankshaft assembly. However, the actual smoothness of an engine’s operation also depends on balancing, piston weight, ignition, clutch, flywheel, and the overall engine design.
The designation “Touring Evo” denotes the current stage of development within the BGM PRO Touring series. The focus is not on a single detail change, but rather on the manufacturing of the complete crankshaft assembly, which has been refined over the years.
Particular emphasis is placed on the connection between the crankshaft journals and the crankpins. In addition to the precisely defined press fit, the crankpin is chemically secured with a high-strength anaerobic Loctite bonding adhesive. This additional securing measure increases the crankshaft journals’ resistance to twisting under high loads and makes the Evo version particularly suitable for high-performance, high-torque engines.
Within the well-known BGM PRO Touring product line, the “Evo” designation thus signifies not merely a cosmetic model update, but a concrete technical advancement in manufacturing and joining technology.
The BGM PRO Touring Evo crankshafts are constructed with forged crank webs. The connecting rod is also forged. The forged structure ensures high material density and is very well suited for the varying loads of a high-performance two-stroke engine.
Just as important as the material is the connection between the crankshaft journals and the main bearings. The manufacturing and assembly processes for BGM PRO crankshafts have been continuously refined over the years. In addition to a precisely defined press fit, the main journal is now also secured with a high-strength anaerobic bonding adhesive from Loctite.
This additional chemical lock—often referred to as “chemical welding”—complements the mechanical press fit and enhances resistance to crankshaft half-shaft twisting under high loads. This is a particularly important advantage in large-displacement engines with high torque, severe load cycles, and performance-oriented applications.
The lower connecting rod bearing is supplied with fuel mixture via two large lubrication slots and additional lateral lubrication areas. Together with the racing bearing and the lateral thrust washers, this creates a connecting rod bearing assembly designed for high load capacity.
The upper connecting rod bearing is supplied via two lubrication holes. An INA piston pin bearing is included in the scope of delivery.
The connecting rod is designed for a piston pin with a Ø16 mm diameter. This means the rod fits directly onto corresponding pistons in modern large-frame cylinders.
If a piston with a 15-mm piston pin is to be used, this can be achieved with a conversion piston pin bearing designed for this purpose.
On the clutch side, the BGM031128G uses the conventional PX mounting. This is particularly interesting when used with the Polini 244: Polini’s own 60/127 shaft features special splines and is designed for a corresponding Polini clutch hub.
With the BGM PRO shaft, however, you retain the freedom to choose from the standard clutch systems compatible with the PX200 crankshaft stub.
The BGM PRO Touring crankshaft has been in use for years in numerous high-performance PX200 engines. Real-world setups producing over 30 PS and more than 35 Nm of torque demonstrate that the shaft functions reliably even with significantly increased engine power.
The combination of forged crankshaft journals, forged connecting rods, high-quality connecting rod bearings, and the precise, chemically hardened crankpins provides an exceptionally robust foundation for this. It is precisely this manufacturing quality—refined over many years—that makes the crankshaft attractive not only for classic touring engines but also for very high-performance street and sport setups.
For high-performance engines, we also recommend a properly balanced rotating mass. A pole wheel weighing up to approximately 2,300 g has proven to be an excellent combination of smooth operation, responsiveness, and low dynamic stress in our setups.
| Manufacturer | BGM PRO |
|---|---|
| Part Number | BGM031128G |
| Type | Touring Evo Rotary Valve Crankshaft |
| Evo Version | Current evolution stage with advanced joining technology and additional chemical connecting-rod pin protection |
| Stroke | 60 mm |
| Connecting rod length | 128 mm |
| Standard PX200 connecting rod length for comparison | 110 mm |
| Piston pin | Ø16 mm |
| Ø15-mm piston pin | Possible with a suitable conversion piston pin bearing |
| Intake control | Rotary valve |
| Cheek width | PX200 design |
| Intake layout | Deep inlet shoulder for large clear cross-section |
| Inlet closure | Approx. 58° after TDC on a typical PX cylinder head, depending on the cylinder head |
| Recommended intake start as a tuning starting point | Approx. 120° before TDC |
| Crankpin | Forged |
| Connecting rods | Forged |
| Connecting pin joint | Precision press fit with additional chemical locking using high-strength Loctite bonding adhesive |
| Upper connecting rod bearing | INA piston pin bearing included |
| Clutch housing | Conventional PX200 crankshaft stub |
| Typical cylinders | Quattrini M244, VMC Explorer 244, Polini 244, and comparable 60-mm long-connecting-rod designs |
| Vehicles | Vespa PX200, Rally200 with Ducati ignition, Cosa200, Motovespa TX200 |
| Additional Applications | Appropriately prepared or bored-out 80–150-cm³ large-frame casings |
The BGM PRO Touring Evo BGM031128G is a specialized crankshaft for modern, large-displacement PX200 rotary engines. A 60 mm stroke and 128 mm connecting rod provide the geometric basis for cylinders such as the Quattrini M244, VMC Explorer 244, and Polini 244.
The long connecting rod offers significantly more freedom in cylinder positioning and, consequently, in the choice of valve timing angles. At the same time, the conventional PX clutch stub allows for a wide selection of compatible clutch systems.
Of particular interest is the deeply machined intake shoulder on the crankcase: it provides a large amount of free cross-sectional area directly below the rotary valve inlet. This allows for high-performance setups without having to rely exclusively on extremely long intake valve opening times to achieve the required flow rate. This makes the crankshaft particularly attractive for powerful yet still drivable street engines.
Added to this is the crankshaft assembly’s manufacturing process, which has been refined over the years. The crankpin is not only precisely press-fitted but also chemically secured with high-strength Loctite adhesive. Together with the forged components and the sophisticated bearing arrangement, this results in a crankshaft that has proven itself convincingly even in setups with very high power and torque.
DE | €
