Crank for 75Polini?

I’m restoring my first Vespa, a 50 S from 1965.
I’m not very experienced so I would like a „pro“ to tell me what kind of crank I should use with this setup:
-75cc Polini cylinder
-New trasmission (not very „much“ though)
-Banana exhaust
-19mm dell’orto carb
-Reinforced clutch

Do you recommend an original crank (with end-bearing) or a racing-crank?

I’ve read in the instruction-manual from Polini that they recommend NOT to „open“ the valve timing!!!
It’s important for me that my engine start easily and have a good acceleration, but it would be nice if the top speed was over 65km/h.

Can someone tell me the positive and negative things about the two types of cranks?

Maybe you have some other tips?

I’m very greatfull for everything that can help me! Thanks a lot.
Look forward to go rolling on my 10" wheels![:rotate:]
Mats Alfsen, Norway

Thank you. I will use an standard crank!


I don’t advice you to open the valve timing. If you open it it is true that you will have more high rpm power but at the same time your low will suffer a little.
In a bigger engine there is a bigger margine of low end power but with the 75 when you have less low can be problematic.
You could open then just a little, the gain wouldn’t be noticeble but the price yes. At that point of price it would be wiser to buy a 85cc. with 19 carb. So I would use a standard crank.