The BGM ORIGINAL standard crankshaft with a 19 mm taper is designed for classic Vespa small-frame engines with a 51 mm stroke. It is suitable for a faithful-to-the-original 125 cm³ engine build as well as for a robust 133 cm³ street setup, where smooth operation, responsive throttle, and long service life are the top priorities.
BGM ORIGINAL
19 mm taper
51 mm stroke
97 mm connecting rod
Standard valve angle
Key Technical Specifications
Design: Rotary-slide crankshaft with standard crank angle
Cone: 19 mm
Stroke: 51 mm
Connecting rod length: 97 mm
Upper connecting rod bearing: 15 mm
Designed for Vespa small-frame engines with a small taper
Application
This crankshaft is intended for riders who want to build their Vespa small-frame engine close to stock specifications or achieve durable street tuning with moderate RPM levels. The valve timing angles correspond to those of a standard 125-cm³ crankshaft, delivering well-controlled performance characteristics with smooth idling, good responsiveness, and straightforward tuning.
Typical Applications
Authentic rebuilds of Vespa PV125, ET3 125, PK80 S, and PK125 S engines
Stock-style 125 cm³ engines with original or comparable ignition systems
Reliable 133 cm³ street setups with tuning suitable for everyday use
Engine overhauls where the old stock crankshaft is to be replaced
Compatible Vehicles and Licensed Models
The following list of vehicles is divided into those with a direct match and those requiring inspection due to licensed or modified variants. The decisive factors are always the engine type, existing ignition system, pole wheel, and the 19-mm cone on the alternator side.
| Model |
Engine Type |
Note |
| Vespa 125 Primavera |
VMA2T |
Direct 125-cm³ small-frame application with 51 mm stroke |
| Vespa 125 ET3 Primavera |
VMB1T |
Direct 125-cm³ small-frame application with 51 mm stroke |
| Vespa PK 80 S |
V8X5T |
Check for compatible 19-mm ignition and 51-mm stroke configuration |
| Vespa PK 125 |
VMX1T |
Check for 19-mm cone and existing pole wheel |
| Vespa PK 125 S |
VMX5T |
Typical application for this crankshaft design |
| Model |
Engine Type |
Note |
| Vespa 90 Super Sprint |
V9SS1T |
Check only if the 51-mm assembly, 19-mm cone, and 15-mm piston pin bearing are compatible |
| Vespa 125 Nuova |
VMA1T |
Technically related to the earlier 125-cm³ small-frame design; check the cone and ignition system before ordering |
| Vespa PK 125 ETS |
VMS1T |
Use only with a properly configured ignition system and pole wheel; do not use as a blanket replacement for all ETS configurations |
For PK ETS, PK XL, and modified engines, different crankshaft journals, bearing seats, and oil seal seats may be installed. Check the existing shaft and ignition system before ordering.
| Model |
Engine |
Note |
| Motovespa 125 Primavera |
9NK |
Spanish licensed model; check for 51-mm stroke and 19-mm cone configuration |
| Motovespa 125 Primavera |
9NV |
Spanish licensed model; check engine number and ignition system |
| Motovespa 75 Primavera |
9PK / 9PN |
Check only if equipped with the corresponding 51-mm setup or converted to a 125-cm³ configuration |
| Motovespa 75 PR |
9PR |
Include only as a license model application subject to inspection if the cone, stroke, and ignition system match |
For Motovespa vehicles, the year of manufacture, engine identification number, and existing ignition system are particularly important. Spanish licensed models may differ from Italian Piaggio models depending on the series.
Suitable for 133 cm³ street setups on a compatible Vespa small-frame engine case
The key specifications are a 51 mm stroke, 97 mm connecting rod, and 15 mm upper connecting rod bearing
The ignition system and magneto must be compatible with the 19-mm cone
When converting 50, 75, 80, or 90 cm³ engines, check the entire engine configuration
Material and Manufacturing
BGM ORIGINAL crankshafts are forged. During forging, the material is compacted under heat and high pressure. This results in a durable material with good heat dissipation and high dimensional stability. Especially in air-cooled two-stroke engines, a sturdy crankshaft is essential for smooth engine operation and long-term durability.
Standard cam angles for smooth street riding
The crank angles correspond to those of a standard 125-cm³ crankshaft. This ensures the engine remains easy to tune and retains its stock-like characteristics. This is particularly appealing to riders who do not want to build an engine focused on extreme RPMs, but are instead looking for a reliable foundation for everyday use, touring, and classic street tuning.
When is the standard version a good choice?
When the engine is to be built to be unobtrusive, easy to ride, and durable
When intake behavior close to stock is desired
When a 125 cm³ engine is being rebuilt true to the original
When a moderate 133 cm³ street setup without significantly extended intake times is planned
19 mm cone: suitable for original small-frame designs
The crankshaft features the so-called “small” 19 mm cone. This design can be identified by the diameter of the shaft seal surface on the alternator side. This is the surface on the crankshaft stub between the cone and the alternator bearing seat.
| Cone |
19 mm |
| Stroke |
51 mm |
| Connecting rod length |
97 mm |
| Upper connecting rod bearing |
15 mm |
| Valve angle |
Standard |
Tuning and Lightweight Flywheels
Thanks to the forged material, the crankshaft can also be used with lighter flywheels in suitable street setups. A reduced flywheel weight makes the engine more responsive and improves throttle response. It is important to have a well-balanced combination of crankshaft, ignition, flywheel weight, cylinder, and desired RPM range.
Note on the appropriate performance level
The 19-mm cone version is the right choice for stock and solidly built street setups with the appropriate ignition system. Those planning a significantly sportier engine with very high RPMs, greater tuning potential, and a modern ignition system can alternatively upgrade to a crankshaft with a 20-mm cone. The larger cone provides additional headroom for such upgrades. The ignition system must be adjusted accordingly to accommodate the 20-mm cone.
Alternative for More Power
For engines with higher power targets, the same basic design is also available as a racing crankshaft with an extended intake timing angle. This variant is recommended if larger carburetor bore sizes, sportier cylinders, and a more high-rpm-oriented engine configuration are planned.
Installation Instructions
Check the cone size of the existing ignition system before installation.
Always inspect bearings, shaft seals, and retaining parts during an engine overhaul.
Check the crankcase, rotary valve surface, and intake area for wear before installation.
Install the magneto arm only with the correct groove, matching cone, and proper torque.
Conclusion
The BGM ORIGINAL Standard Crankshaft (Ø19 mm) provides a solid foundation for Vespa small-frame engines with characteristics close to stock. It is compatible with original 125-cm³ setups, many 19-mm small-frame configurations, and moderate 133-cm³ street tuning. Those who later wish to pursue higher RPM and power will find the appropriate next upgrade in the 20-mm tapered variant or the racing crankshaft.
FAQ
It is designed for Vespa small-frame engines with a 51-mm stroke and a 19-mm taper, such as the PV125, ET3 125, PK80 S, and PK125 S with compatible ignition systems.
It may fit Motovespa small-frame licensed models such as the 125 Primavera 9NK or 9NV if the stroke, connecting rod length, 19-mm taper, ignition system, and magneto match. The engine number and existing crankshaft should be checked before ordering.
The 19 mm cone is the small cone design on the alternator side of the crankshaft. It must be compatible with the ignition system and the pole wheel being used.
Yes, it is suitable for robust 133 cm³ street setups with moderate RPM levels. For sportier setups with higher power targets, a race crankshaft or a 20-mm cone version is the better choice.
The 20-mm conical version is recommended when building a significantly sportier engine with higher RPM levels, more extensive tuning, and a compatible ignition system.
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