Engine Housing - POLINI Diaphragm Intake - Vespa PX125/150 Elestart and Motovespa PX125/150 Iris, 125/150 CL
POLINI OEM: 170.0601
The completely redesigned POLINI engine cases with diaphragm intake for the Vespa PX125/150 Elestart as well as the Spanish Motovespa models PX125 Iris (99M), PX150 Iris (75M), 125 CL (9CL), and 150 CL (9NC) combine modern flow technology with the robustness of classic large-frame engines. They are designed as performance-oriented replacements for the original Piaggio or Motovespa engine cases and provide a solid foundation for powerful street and racing setups. Polini OEM: 170.0601
For PX125/150 Elestart
For Motovespa Iris/CL
Reed intake 28/30 mm
CFD-optimized flow
Intake design and carburetor mount
Instead of the classic rotary valve inlet, POLINI uses a newly designed diaphragm inlet for these engine cases. The flat diaphragm channel replaces the rotary valve-dependent control system, thereby eliminating all problems that can arise from worn or damaged inlet sealing surfaces.
Switch from the standard rotary valve to a modern diaphragm system with a flat diaphragm.
Significantly more stable mixture formation and cleaner response across the entire usable RPM range.
Designed for racing diaphragm blocks with 28/30 mm carburetors—ideal for performance-oriented setups on PX125/150 Elestart and Motovespa Iris/CL.
Also available: Racing diaphragm block in pyramid shape without separate lubrication, with its own intake manifold for 28/30 mm.
Despite the new intake design, the casings remain fully compatible with original Vespa and Motovespa components on the periphery. This simplifies the conversion from the stock engine casing and allows existing attachments to be reused, provided they are suitable for the desired performance level.
Mechanical and Structural Optimizations
POLINI did not simply copy the engine cases, but redesigned them in many respects. The two case halves are numbered as a pair at the factory and machined together. This ensures that bearings and sealing surfaces are precisely aligned with each other, which noticeably improves smoothness and durability.
Casing halves are manufactured and numbered as a pair to ensure a perfect bearing fit and parallel contact surfaces.
The crankcase and overflow chamber are designed for optimal gas flow using CFD simulation.
The swingarm has been redesigned and reinforced via FEM analysis; additional ribs and material reserves allow for the use of wider rear tires.
The area around the rear axle stub is reinforced in the transmission housing to accommodate the higher torque of performance-enhanced engines.
Bearings, Seals, and Bolts
Typical weak points of the original PX and Motovespa housings have also been addressed. On the clutch side, the design has been modified so that the radial seal ring can no longer migrate unnoticed from its seat. A precisely machined steel flange provides additional support for the crankshaft bearing.
Modified design on the clutch side to reliably prevent the oil seal from shifting out of place.
Ground steel flanges as a support for the crankshaft bearing on the clutch side, for high dimensional stability.
Larger crankshaft bearing on the ignition side (25 x 52 x 15 millimeters) for smoother operation and longer service life.
Instead of conventional through-bolts (M7), M8 hex head bolts are used, which increases the rigidity of the entire housing assembly.
The central housing gasket is omitted; instead, the two housing halves rest directly on top of each other with an enlarged contact surface. In combination with a suitable sealant, this results in a very stable and largely temperature-insensitive connection—a clear advantage over the worn-out aluminum housings of the first production runs.
Chassis Mounting and Peripherals
In addition to pure engine performance, POLINI also focuses on the peripherals. For example, the mounting points for the shock absorber and cylinder base have been specifically reinforced to provide a solid foundation for sporty suspension setups and higher continuous power output.
Reinforced shock absorber mount, suitable for stiffer suspension setups and touring configurations.
Reinforced cylinder mounting surface for high clamping forces and stable sealing conditions with tuned cylinders.
Prepared for an electric starter—ideal for the PX125/150 Elestart and appropriately equipped Motovespa models.
The transmission oil filler neck has been repositioned to increase the oil volume and thus the lubrication reserve.
Material and Manufacturing Quality
The engine casings are die-cast from a high-quality Al Si10 Mg T6 aluminum alloy. This is followed by heat treatment to optimize the mechanical properties.
Al Si10 Mg T6 light metal alloy for high strength at moderate weight.
Heat treatment ensures stable material properties even at high continuous operating temperatures.
Enlarged sealing surfaces and reinforced areas at all critical points.
Applications
The POLINI engine cases for the Vespa PX125/150 Elestart and the corresponding Motovespa models PX125/PX150 Iris and 125/150 CL are designed as a platform for high-performance street and racing engines. Whether a powerful touring engine with a reed valve intake or an uncompromising racing setup—the combination of a modern intake design, optimized flow, and reinforced structure offers ample reserves for setups far beyond stock performance, without sacrificing the Vespa character. Polini OEM: 170.0601
FAQ: POLINI Engine Case PX125/150 Elestart and Motovespa Iris/CL
Frequently Asked Questions
How does the POLINI crankcase differ from the original PX125/150 or Motovespa Iris/CL crankcase?
In addition to the switch to a diaphragm intake, the flow, bearings, and structure have been completely redesigned. The cases are sturdier, offer space for wider tires and larger bearings, and feature an optimized oil supply, yet remain compatible with most Vespa and Motovespa components.
Do I have to use a 28/30-millimeter carburetor?
The housing is designed for diaphragm systems in this size range, as this is where the potential is best utilized. Smaller carburetors are technically possible but do not fully exploit the system’s advantages.
What about separate lubrication?
Variants with separate lubrication are available for the flat diaphragm intake. Additionally, there is a pyramid-shaped diaphragm block without an oil pump that has its own intake manifold. This allows for either mixed or separate lubrication depending on the configuration.
What is the advantage of the larger crankshaft bearing on the ignition side?
The larger bearing improves smoothness and increases service life at high RPMs and with powerful cylinders. Especially in combination with heavy fan wheels or high-RPM operation, this is a plus for operational reliability.
Who should consider switching to POLINI engine cases?
This is particularly relevant for new builds and engines whose performance targets are significantly higher than stock. If you’re running a modern reed valve intake, powerful cylinders, and matching exhaust systems, this provides a base casing that won’t act as a limiting factor in your setup.
What is the POLINI OEM number for this engine case?
The POLINI OEM number is 170.0601.
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