Vespa V50-125, PK50-125/S Prim ET3 Smallframe SIP Crankcase - 3-hole Flywheel Side 20mm

Extensively revised engine housing for Vespa Smallframe models, newly developed and produced by SIP.

Many Vespa fans consider the smallframe models motor to be the finest amongst those produced by PIAGGIO. For this reason, and many more, we have decided to have revised and updated versions produced.

The SIP smallframe motor cases are, despite their extensive strengthening, almost identical in appearance to the original items. These essential improvements qualify this motor as a first choice when replacing/upgrading your original, or as a basis for any ambitious tuning project.
- Suitable as an original replacement
- Lots of material on overflows and inlet for tuning
- Reinforced and durable design
Both the transfer and inlet ports share their internal dimensions with the originals, with lots of potential for reshaping and enlarging. The material surrounding these areas has been increased to facilitate 'out of the box' port enlargement work, without the need for any extra material to be added by expensive welding. The disc valve inlets sealing surface has also been increased and can now be enlarged over both motor halves. The openings for the casing bolts on its lower half have been relocated externally to allow enlargement, which in turn facilitates the use of crankshafts with larger webs and/or increased stroke. The reinforced swing arm assembly has been intensively laboratory tested and approved for its durability in all situations and resistance to cracking and breakage. In addition this new motor type was successfully test-run at almost full-throttle for two whole weeks in combination with a POLINI 133cc cylinder, 24mm carburettor and a PM exhaust. All temperature, corrosion and road tests were also passed with flying colours and the customer feedback also helped refine the final product of our labours to perfection. The overall design is based upon the PK range motor, with a three stud inlet manifold mounting and the exhaust mounting opening located on the lower side of the swing arm assembly. If a Vespa 125/PV/ET-3 motor is being replaced our Serie Pro manifold adapters (inlet : #21500060, #2150007-, #21500080) can be used to ensure compatibility. Another upgrade is the use of high-end Italian produced motor mounting bushes for a tight suspension. Before being dispatched in a sturdy double-strength box these motors are carefully checked for correct dimensioning, production quality and completeness by one of our team.

The different versions

We have two versions of these motor cases available, the main difference being the diameter of the area where the flywheel side bearing is located. : Motor #24320000 is compatible with the ETS series crankshaft and the PX bearing. - Motor #24310000 is suited for use with the bearing fitted to all Vespa 50-125/PV/ET-3/PK 50-125 motors with its 47mm outer diameter.We also have the version with an original two-stud carburettor manifold fixing available since 2019. These casings combine the advantages of the SIP PK type with many distinguishing features of the early smallframe engine casings: two-stud carburettor manifold attachment, circular inlet port and smaller inlet port on the disc-valve surface, three additional attachment threads for two-coil stator plates found on very early models. This enables an older engine to be reconstructed using the SIP engine casings, while remaining 100% original. The part approval documentation, included with every set of casings, certifies their validity as original components when rebuilding a Vespa 50-125cc smallframe engine. A welcome advantage for scooter dealers when satisfying vehicle guarantees!

The SIP EVO engine casings possess increased material surrounding the flywheel-side transfer ports facilitating enlargement and matching modifications. This will require the stator plate to be adapted to fit properly. The inlet port is also provided with more material allowing machining and tuning. The ventilation channel, usually located on the cylinder base gasket surface, has been omitted. The EVO version is also available as an attractive 'Black Edition'.
Conclusion: your smallframe is no longer at risk of dying due to engine damage. And at a very good price / performance ratio!
- They are suitable for Vespa 50-125/PV/ET-3 (Adapter manifold or 2-stud versions) and also all PK models.
- Original appearance and port dimensioning, oversized gasket surface areas, extra material included to enable extensive port/crankcase enlargement.
- The cylinder base gasket surface area has been spread over both motor halves facilitating maximum gasket area following port enlargement.
- Increased motor case thickness and internal ribbing, reinforced crankcase and swing arm assembly.
- In the EVO version with extra casing material surrounding both the inlet and flywheel-side transfer ports and revised ventilation channel.
- Three engine casing types for a flywheel-side bearing with a 47mm diameter (20mm shaft), as a two or three-stud carburettor manifold fixing and a 38mm diameter (25mm ETS crankshaft) version available.
- The swing arm assembly has been restructured and reinforced along its inner edge and compatible with all 3.00 – 3.50/10 sized tyres. 3.50-10” tyres fit without modifications.
- The seat of the primary drives bearing seat has also been optimised and possesses a diameter of 57.5mm for compatibility with all suitable primary drive/repair kit types.
- Overall construction laboratory and road tested and optimised for rigidity and durability.
- Replaceable bronze sleeve for the gear selector shaft.
- Engine studs for the brake assembly, the motor casing halves (2x) and mounting studs suitable for a 125cc cylinder are included in the delivery.
- Internal kick-starter buffers and rubber bushes for the swing arm and shock absorber mounting assemblies are also included and pre-mounted.
- The EVO version is also available as a 'Black Edition'.
- The two-stud carburettor manifold fixing type includes full part approval documentation from the German testing authorities.

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