New Polini Vespa P-range crankshafts turned up
New from Polini and already arrived at Scooter Center are the P-range crankshafts.
Available are the Polini Vespa cranks in these specs:
- Vespa P200, stroke 57 mm, 110 mm con rod
- Vespa P200, stroke 60 mm, 110 mm con rod
- Vespa P125, stroke 57 mm, 105 mm con rod
En detail:
After these arrived we took a closer look. at these.
On a first sight the rotary valve inlet comes to our attention. This is heavily machined and lots of material has gone.
Then the heavy cut comes to our attention. This gives a very abrupt closing. This is good because on some other designs a build in wharf spits the fuel out . The window oppsite the rootary valve is very big to get the balancing right.
The P125 and P2 57 mm stroke are equipped with a 22 mm big end pin. While the 60 mm version comes with a 20 mm big end pin to have enough meat above the pin.
The cutaway on the rotary valve crank webdefines how long the inlet is opened. On a new P2 engine casing we had 110° before top dead centre and 75° after top dead centre.
The opening period of 185° is very sportive.
On the Px 125 it gave a 110° before top dead centre and 63° after top dead centre. The top dead centre was found with our timing degree disc.
The width of the rotary valve side wasn’t touched by Polini. And like on a original crankshaft it is 17 mm.
Polini advertises the crank as balanced to get rid of nasty vibratins, so we checked what we found here. So we check the balancing factor using the P2 crank with 57 mm stroke.
On the jig it nearly stops at 12 h.
The balancing factor can be used as an indication of how smooth the engine will run.
If you want to try and calculate a little, we have some readings for you here.
The translational part of the con rod has a weight of 60.25gr
The counter weight that need to be put on the crankshaft to make a stand still at every positioning possible is 
104,35gr
