Polini 130 Install
Vespa Small Frame - Polini 130 Install
The Polini kit, like the Malossi can be bolted right on to the casing, but to get its true potential the crankcase mouth transfers need to be opened up and matched to the barrel. That involves a full engine strip so an alternative is to simply mount the barrel. The directions are the same from here onwards whether you changed the transfers or not. If you are starting from a built up bike, here's a guide to removing the original barrel and piston.
The kit I had came off a running bike so I didn't have to mess around with fitting the rings. If yours is a new kit you'll have to install the rings. A quick guide from a standard small frame piston can be found here and the idea is the same for the Polini piston.
This section starts after the cases have been ported and the original barrel has been discarded. Three things are very important to make this kit run well.
(1) Porting the cases. This really unlocks the power of the kit. If the cases are not ported you'll still get a faster bike but it will the kit won't perform as well as it could.
(2) Changing the stock timing. The Polini kit requires a slightly advanced timing point compared to a stock Primavera. The Polini requires 16 degrees BTDC compared to the stock 24 degrees BTDC.
(3) Changing the main jet in the carburetor. Since the bike can now burn more fuel because of a more efficient cylinder the main jet must be changed to allow that extra fuel to come through the carb.
Use the new Polini base gasket and slip it down over the studs. Make sure it aligns with the transfers. Because my casing transfers were modified, I opened out the transfer areas of the gasket with an exacto knife to match the transfers beneath. A modified Vespa one works just as well as the Polini original. Fit the small end bearing after smearing a little two stroke oil over it. It should slide tightly into the small end of the con rod.
The piston can be installed in two directions and it is imperative that it faces the correct way. Look on the dome of the piston and you should see a small arrow. This must point towards the exhaust pipe which is up and away from the swing arm pivot as shown above.
While supporting the piston, carefully slide the wrist pin into place. If it is especially stubborn you can heat the piston with a hot wet rag which will make the metal expand slightly and allow the wrist pin a little more breathing room. Don't be tempted to hammer it in.
Polini makes wire wrist pin end clips which are a bit of a pain to fit. Make sure they both fit squarely in their grooves. I also rotate them so that the wire end is in line with the piston length (not shown in the picture above).
Now comes the barrel. Carefully look at the bore of the barrel and if you have gasoline and compressed air available give it a good clean and blow out any debris. Rub some two stroke oil around the inside bore, and fit the barrel over the tops of the cylinder studs. The barrel can go on in many different directions as the studs are in a square format. Make sure the exhaust port is facing up and away from the swing arm.