Modern Vespa

Well

Being the "garage womble" that i am, I was looking through my bits the other r evening and came across the following bits

PX125 engine mostly complete (I have the bits necessary
150 "5 port" cylinder, knackered piston and no head
polini 180 head
P200 crank


do i.....
A - rebore the 150cc with a polini piston to utilise the head
B - stick them back in the corner to gather more dust
C - ask you fine chaps for suggestions of what piston to drop in and whether to use the P200 crank as its 1mm longer stroke


suggestions and opinions appreciated

If you bore the 150 to 63mm, there is a downside that it can change the port location - this is because they don't necessarily come in to the bore straight. There are other downsides apparently but I can't recall the rest just now.

The VMC Stelvio cast iron 177 is cheap and meant to be pretty good so there's an option.
Will you get away with a hone, or does it definitely need a rebore? What's the cost of that including a new piston? I think the LML pistons for that kit are pretty good iirc, with thinner rings than the Piaggio ones. And you'd have to be able to pick up a head for next to nothing, surely.

200 crank in a 150 case can work (and be beneficial) although the stroke will be the same, not 1mm different. You need a (nominal) 5mm base packer to make up for the 5mm longer rod.
You also need to remove the 'lip' from the crank... this is how they managed to get a bigger intake when they made the 200 cases. The crank is basically the same but with extra material to make it wider on the sealing surface (have a look at pics of both cranks and you'll see what I mean). Or machine a groove into the case itself, but that's a lot harder.

hi

a 150cc piston and rebore is £60+ and i dont have a 150 head,

a new 150cc kit is around £75. so its not really cost effective to hunt a head for it............. if only all it needed was honing


The fun option would have been reboreing to a "180" or similar, however, as you have indicated that the ports are not guaranteed to maintain orientation i think the likely reality iis ts a non starter and will put these back in the junk box or if anyone needs a barrel and or a head... let me know


thanks