Polini have just released this new cylinder kit for the Vespa PX125/150. The aluminium kit has an unusual head with the choice of two plug locations, it also has 8 fixing points and extra cooling fins.
Cylinder
The 63mm cylinder gives 178cc using a standard 57mm crank, or 187cc if using a 60mm crank (a new 60mm Polini crankshaft is also available). Keeping an engine air-tight is a battle but the Polini kit has eight fixing points for the head, four dowels locate it into position and the usual four studs secure it in place. These extra points not only centralise the head but also ensure the squish is kept to the correct gap.
Head
‘Twin-spark’ is a possibility because head does come with two spark plug holes, one in the regular spark plug location and a central hole. Offset spark plugs were usually used in conjunction with offset squish heads in order to help the wider squish section cool the exhaust side of the piston. Most modern head designs – like the Polini kit have a central squish and chamber and for that layout a central spark plug position is optimal.
In reality you’ll only need one plug though and a brass bolt is supplied to seal the unused hole. If you decide to use the central plug your standard head cowling will need modifying slightly. The fin design of the head is unusual, rather than having a relatively flat/stepped underside, this one has a chunky recess with extra cooling fins to help dissipate the heat.
Piston
The piston is a twin ring design and the kit comes with head and base gaskets, all fittings and everything you need aside from the small end bearing.
Manifold
Exhaust manifolds can be an area of weakness on any alloy kit but this one has extra strength thanks to a steel flanged outlet with four studs connecting it to the barrel. This also means it can be changed if it does suffer wear. The kit is 100% Italian made.
Pricing
57mm/60mm stroke kit: £282
60mm crankshaft: £192
Polini parts are stocked at both Scooter Center and Vespa Time.
Looking good 🙂
Can the second plug hole be used to put in a decompression valve for those of us with weak knees & ankles
No but we recommend removing the piston rings for those weak of leg.