Polini 177 cast iron 3-channel cylinder for Vespa PX
The Polini is the classic racing cylinder for the PX and Sprint 3-channel engines. A very early high torque makes it an all-round cylinder for almost all requirements. It is ideal for so-called "plug-in tuning", i.e. simply changing the cylinder without modifying the rest of the engine.
After the conversion, everyone is amazed at how powerfully such a Vespa engine can accelerate. The powerful torque turns every steep hill into a plain. The only disadvantage is the Polini's lack of revving pleasure. At just around 7000 rpm, the engine runs a little against the wall; a longer gear ratio using a different clutch pinion is definitely recommended here. Then the Polini easily exceeds the 100 km/h mark and the gears can be pulled much longer.
Carburetor selection for city traffic and touring setups
If you only ride in the city, you can use the 24/24SI carburetor of the 200cc models. The carburetor should be run with a 160 main air jet and a BE3 mixing pipe. If the engine still tends to run lean in the upper rev range, a 140-150 main air jet should be fitted. If you want to go on a long tour with the Polini, you should fit a 28-30 mm carburetor for thermal relief. The 177 harmonizes well with exhaust systems that deliver their power quite early, such as the BGM BigBox.
More power thanks to long-stroke shaft and exhaust work
In conjunction with a bgm long-stroke combustion shaft, the power is significantly increased again across the entire rev range. The result is a hefty 187 cc, providing an abundance of power. If you are still not satisfied with this, you can use a file to increase the advance angle, which is already quite small as supplied. The result is an output that can easily exceed 15 kW, depending on the exhaust. For tuning measures that involve enlarging the exhaust window and increasing the working speed, it is advisable to replace the original piston rings with ones from Grand Sport. These are much less susceptible to breakage and can withstand the increased loads well. For further performance increases above the 25 hp mark, there is also a complete piston with much thinner rings from Grand Sport.
TIP
: Please always fit piston rings carefully. Piston rings made of cast material are only elastic to a limited extent and break relatively quickly.
Some pistons have trapezoidal profiled piston rings (so-called keystone rings), these only fit in one installation position. If the ring does not move freely, please loosen it carefully and reinstall it 'upside down'.
Very helpful tools for working on the cylinder and/or piston are:
- Piston ring compressor BUZZETTI Ø=45-90mm BU5040
- Piston ring pliers BU5045
- Disassembly tool for piston pin UNIVERSAL- Ø=13, 15, 16, 19, 22mm 7674333
DE | €
