Scooterotica

what is the longest stroke crank that will fit a PX125 without any machining ?

I suppose this is like asking where does the univese end, nobody knows !

60mm

Is a 62 mm possible with a bit of machining I know its quite common on a Lambretta casing but can it be done to a Vespa casing?

gadgetman wrote:what is the longest stroke crank that will fit a PX125 without any machining ?

Bin the PX and get a Smallframe you can get 56mm cranks for them now. The 56mm crank (MAX) combined with a 64mm bore (MAX) gives you 180cc of insanity. All this is brought to you and touched by smallframe God Mr Lauro Caforio of Falc Racing. Very pricey but ultimate power and will leave 99.9% of scooters in a haze of 2 stroke smoke.

Unless you are using a reed none that I know of. You will either have to machine a groove in the case(best) or machine the lip off a p2 crank.
Best machine groove because then you can port a much wider inlet.
You can get 62mm by using eccentic DRT pin.
If reed SIP do a 60 that goes straight in with PX rod.
Recommend using p2 crank though because longer rod. Bit of dicking about with packers,longer studs and conversion small end bearing but worth it I think. 105mm too short on 62mm.

At the momen its a Quattrini 172 MIXL direct reed induction mid twenties bhp/ high teens lbs/ft torque and I am wanting to squeeze a bit more out of it without turning it into a racer with no bottom end, so if I am going to rebuild it with a new longstroke crank I want to get the longest stroke without having to spend a fortune on having the casing welded and machined. However if it's a straight forward conversion to go to 62 mm then it's a no brainer.