Long-ratio version for the straight-toothed FAIO / EGIG PERFORMANCE Z52 primary sprocket. Results in a primary gear ratio of 2.74.
The FAIO / EGIG PERFORMANCE Poligon primary pinions with 17, 18, or 19 teeth are designed for the straight-toothed FAIO / EGIG Z52 primary sprocket. Depending on the variant selected, this results in a primary gear ratio of 3.06, 2.89, or 2.74.
The unusually low number of teeth allows for a robust tooth geometry with a wide tooth base. At the same time, the Poligon connection transmits engine torque via a positive-lock engagement between the crankshaft and the primary pinion. As a result, the extremely high tightening torque required to generate the necessary frictional engagement in a conventional tapered connection is not necessary.
FAIO / EGIG PERFORMANCE Z17 / Z18 / Z19 for Z52 primary sprocket Polygonal Mounting straight-toothed Polygon crankshaft required
With the three primary sprockets, the Z52 primary sprocket can be specifically adapted to the engine’s character, RPM range, gear ratios, tire size, and intended use.
| Primary Sprockets | Primary sprocket | Calculation | Gear Ratio | Basic Characteristics |
|---|---|---|---|---|
| Z17 | Z52 | 52/17 | 3.06 | Shortest pitch with high tensile strength and easier connection to the track |
| Z18 | Z52 | 52/18 | 2.89 | A well-balanced mid-range option for many high-performance street engines |
| Z19 | Z52 | 52/19 | 2.74 | Longest gear ratio for engines with a wide power band and high torque |
The gear ratio is calculated by dividing the number of teeth on the primary sprocket by the number of teeth on the primary pinion. A higher number indicates a shorter gear ratio.
The 17-tooth primary pinion, when paired with the Z52 primary sprocket, results in a gear ratio of 3.06. This makes it the shortest of the three possible variants.
The shorter gear ratio enhances acceleration and gear engagement. It is particularly advantageous when the engine does not reach its usable torque until higher RPMs, when the vehicle is driven in a sporty manner, or when a longer gear ratio in fourth gear cannot be safely maintained.
The Z18 pinion, when paired with the Z52 primary sprocket, results in a gear ratio of 2.89. It falls between the other two variants and offers a balanced compromise between acceleration, gear engagement, and final drive ratio.
This ratio is suitable for many high-performance street and touring engines that have sufficient torque but do not require a ratio as long as that provided by the Z19 pinion.
The Z19 primary sprocket results in a gear ratio of 2.74. It is the longest combination within the Z52 system.
This variant requires an engine with a wide usable RPM range and sufficient torque. With the appropriate gear ratio, the longer primary gear ratio can reduce engine RPM at cruising speeds and better utilize the engine’s speed potential.
The appropriate primary gear ratio does not depend solely on the engine’s maximum power output. The decisive factors are how early the engine delivers its torque and over what RPM range.
Classic Vespa small-frame primary gear ratios often use significantly higher numbers of teeth. The FAIO/EGIG system deliberately uses fewer, but larger, teeth.
With the center distance remaining unchanged, this allows the individual teeth to be designed to be stronger. In particular, the tooth root receives more material. It is precisely this area that is subjected to heavy stress during high torque and rapid load changes.
The primary pinions have straight-tooth profiles and must only be combined with the corresponding straight-tooth FAIO / EGIG primary gear Z52.
Unlike helical gearing, straight-toothed gear pairs do not generate additional axial forces. As a result, the crankshaft bearings, clutch, and locking elements are not subjected to lateral forces caused by the gearing.
In a conventional Vespa small-frame primary pinion, torque is transmitted via the interference fit between the pinion and the crankshaft cone. The two conical surfaces must be pressed together with high axial preload.
When the connection is installed correctly, the disc spring—often called a half-moon spring—does not transmit engine torque. It positions the primary pinion during installation and prevents it from twisting on the crankshaft when the mounting nut is tightened.
To establish sufficient frictional engagement on the taper for high-performance engines, tightening torques of up to approximately 90 Nm may be required, depending on the specific design used.
This high preload is generated via the retaining nut and the relatively fine thread of the crankshaft. This places significant stress on the thread, especially during repeated assembly and disassembly.
The FAIO/EGIG polygonal design does not rely on a force-fit conical seat. The primary pinion and crankshaft engage in a form-fit via a precisely shaped polygonal contour.
The engine torque is transmitted directly via this profile. The mounting nut must primarily hold the primary pinion in position axially. It does not first need to generate the frictional engagement required for torque transmission on a cone by applying an extremely high tightening torque.
The specified tightening torque for the polygonal fastening must be observed in accordance with the manufacturer’s instructions.
Poligon primary sprockets require a crankshaft with the matching polygonal counter-contour. They cannot be mounted on a conventional Vespa small-frame crankshaft with a tapered mount.
The primary pinions are designed for primary drives that must withstand significantly higher loads than a stock Vespa engine. Typical applications include high-displacement, high-torque engines based on the EGIG 220, Quattrini M200, and comparable designs.
| Primary sprocket | Matching primary pinions | Possible gear ratios |
|---|---|---|
| Z50 | Z20 or Z21 | 2.50 or 2.38 |
| Z52 | Z17, Z18, or Z19 | 3.06 / 2.89 / 2.74 |
The Z17, Z18, and Z19 primary pinions must not be combined with the Z50 primary sprocket. Similarly, the Z20 and Z21 pinions are not intended for use with the Z52 primary sprocket.
The key component is the Vespa small-frame engine, equipped with a matching crankshaft featuring a polygonal mounting and the FAIO / EGIG PERFORMANCE Z52 primary sprocket.
| Manufacturer | FAIO / EGIG PERFORMANCE |
|---|---|
| Component | Primary Sprocket |
| Variants | Z17, Z18, and Z19 |
| Matching primary sprocket | Z52 |
| Tooth Profile | straight-toothed |
| Mounting | Polygon |
| Gear Ratio Z17 | 52/17 = 3.06 |
| Gear ratio Z18 | 52/18 = 2.89 |
| Gear Ratio Z19 | 52/19 = 2.74 |
| Required crankshaft | Crankshaft with compatible FAIO/EGIG polygon mounting |
| Vehicle range | Vespa Smallframe |
| Models | V50, PV125, ET3, PK50, PK80, and PK125 |
| Typical engines | EGIG 220, Quattrini M200, and comparable high-performance small-frame engines |
| Advantage of the Mounting | Positive-lock torque transmission with reduced tightening torque and less stress on the crankshaft thread |
The FAIO / EGIG PERFORMANCE Poligon primary pinions Z17, Z18, and Z19, when used with the Z52 primary sprocket, provide three stepped gear ratios ranging from 3.06 to 2.74. This allows the primary drive to be specifically tailored to the torque, RPM range, and gear ratios of a high-performance Vespa small-frame engine.
Large individual teeth, straight-cut gearing, and the form-fit Poligon mounting make the system particularly suitable for high-displacement engines. Thanks to the form-fit connection between the crankshaft and the primary pinion, no extremely high tightening torque is required to create a tapered fit. This reduces the stress on the crankshaft thread.
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