

Fast forward past the pissed-and-broke joke, I was just thankful the bore was ok. Perhaps I should say mostly ok. Turned out the top edge of the exhaust port had lost a little nicasil. So I thought I may as well grind it out, otherwise it's a new cylinder! And the piston was already a couple of hundred dollars so I was not keen on padding Mr Q's account any further just now.
It went well. I left it at more of an arch than a flat line, when I measured the port timing - an anxious moment - it had arrived at 188/126. Previously was 176/126. The numbers certainly didn't seem ridiculous so that was something of a relief. Scooter Center did a blog in 5 parts building a 252 (they used a Kingwelle crank which has a 128mm rod instead of my 127mm Uncle Tom), and they tried lifting the exhaust to 190 and found power down a couple of horsepower around 5000 using the Polini Box like mine.
So I was slightly anxious I hadn't killed it after all.
Needn't have worried. It was fantastic! With no other changes (except correctly timing it!) you could really feel the extra power right throughout the rev range. But mostly over around about 6-7K rpm, where it just kept accelerating. When I passed a restored Datsun 120Y (makes you feel old!) it actually gave me a bit of a fright as I glanced and saw I was doing 118 and it was still pulling hard!
And the amazing thing, the temperatures seemed lower and more stable than previously. After a 40 minute run mostly around a very relaxed 100km/h, the temps sat between high 330's and 350, which I'm pretty comfortable with.
A very satisfying experience.
Did make me think about the dyno posted by FMP a little while ago, sorry a bit blurry. I was pretty impressed with the Malossi Box vs the Polini, with a fair bit more to give at the higher revs. A mate had a PM pipe on his 221 and the swap to the Malossi Box gave more power all round , including a higher top speed.
Might be one in my future.
https://en.blog.scooter-center.com/alex-builds-a-quattrini-252cc-vespa-engine-5/