Modern Vespa

Guy-François Evrard - trades as J&G 2% Vespa Tuning - has come up with a method to non-destuctively fit a P200 cylinder to a 125/150 case, resulting in a 208cc capacity using mostly stock components.

https://scooterlab.uk/jg-vespa-200-cylinder-conversion-for-the-px125-feature/

He's a clever guy and among other things has been working with Al Harpham on a new version of the Vortex; has done a VMC 177 with 200 bell crank and SI carb that will do 140km/h, and plenty of engine builds. I've known him for a few years and he's been great to bounce ideas off.

https://youtu.be/H6F7VV9cfdQ

I'm interested!

It's intriguing but the SLUK article doesn't fish any details out of him on how he's doing it. Granted, he doesn't want to give away the secret yet, but I'm thinking the article is too far ahead of where he is at on figuring out what to do with the knowledge, business-wise. It's frustrating to read "I did it, but I can't say how or if you will ever be able to do it also. And I won't tell you how much it will cost yet or if you will do it by sending it to me or buying parts, but stay tuned..."

I took it as he created one custom part that he won't explain cause he wants to make money off it by finding a manufacturer/distributor. This article serves the purpose of drawing attention to it to attract those manufacturers to contact him. I have no problem with that if it means eventually this could land online for purchase!

Yeah I don't have a problem with it, but it makes for a non-informative article.

True but it's good to know it's a possibility! Maybe some day we will get more info, then again we are still waiting on more concrete details of the sip viper exhaust they wrote up over a year ago.

I think I have a pretty good idea how he did it, but I guess I shouldn't say either! He deserves to make some money out of it if he can get it to market.

Amazing what guys do in sheds

I think that the better take-away is that our 125 cases will still be a low cost upgrade path. I have spent the better part of a year trying to track down a p200 engine for my sidecar build and having a 200cc upgrade using fairly stock parts would have been wonderful.

As they explain in the video and article, he has extended the stroke. I think that implies that he has created an adapter/riser plate for the head bolts, therefore allowing the cylinder and piston to have the clearance needed. This is purely a guess.

I think your explanation would make the most sense.

Don't forget that if he was to use a 200 crank with 60mm stroke, then the nominal gap between case and cylinder that needed to be filled with a plate would be 6.5mm...

a plate that would bolt into the existing holes adjacent the gasket surface. then m8 studs for the p200 cylinder coming out of the plate. this is purely a guess as i have never played around with it.

Kudos to the guy that i have had limited interaction with through FB. i think it would have been killer 10 years ago. now that BGM/VMC/etc cylinders are out in the market for small blacks, i'm not that excited about strapping a 1-port p200 cylinder to them.

This was my guess, too. With my P200 bell crank, I need about a 5mm spacer on my Stella cases, and it's already decked a little high, which would give him 5-6mm of space to play with in there.

The piece I can't figure out is how he's going to fit a 67mm barrel into an opening that really only wants to take a 63mm barrel without machining, but I don't know P200's, so that could just be my ignorance showing.

If the packer is less than 1cm thick, seems crazy to trust the barrel mating to studs that can't go very deep into the packer/case. Maybe 1 or 2 is in the same location for both cylinders?

I think I'd trust a 5mm stainless steel packer to hold both directions, but at some point, you're going to be hitting the limits of stressing the cases themselves.

He could possibly be using a longer rod crank (which would require a thicker spacer), not sure about that part. Patrick would know for sure but I think you are correct about some studs being in the same place.

Here's a pic from PLC Corse of one of their smallframe Kart cylinder conversions.

I don't think any studs line up as the 200 sits at an angle. If the adapter was steel and 5mm thick for the 110 rod. Studs made like shallow bolts and welded into the adapter and looking like your PLC one but in steel. Skirt cut off the cylinder (like M244) and piston shortened. The PBT would be flush like he describes and it would work. And all be fully reversible.
As said seems pointless when a BGM or Malossi 190 is quicker and torquier than a 200 anyway.

Why does everyone keep saying it's 5mm? It's only 5mm for the rod and 1.5 for the longstroke.

And (again) that's unless he is using a long rod - like the Husqvarna conversion, like the Quattrini 232/244, and probably that PLC above - in which case he can use a 116mm rod and have a 12.5mm packer/adaptor for instance. Plenty of room to house the stud heads.

He also needs to have a crank without quite as wide a lip as the stock 200 to be able to fit inside a 150 case and it's slightly narrower rotary valve.

200 cylinder -1.5mm PBT he said he was using to up compression. This was a left over design feature from the original 200 rally, made for a factory 60mm.

What does PBT mean? Keep seeing you write it but can't work it out.

First time I've heard about a 'factory' 60mm crank, that's cool! Do you know the story behind it? And why they didn't go ahead with it?

piston below top of cylinder.

Cheers Swiss.

No hard facts about the story. Just what I was told a long time ago. The Rally 200 was designed with a 60mm crank and 65mm piston but for some reason it was soon changed to a 57mm and 66.5 piston. It does make sense. Around that time the 180SS had a 60mm crank and the GS160 before it had a 60mm too. It does explain the -1.5mm and the very thin cylinder spigot, nobody would deliberately design that.