The piston is then exposed. Remove the piston by taking out the ring clips each side of the gudgeon pin and pushing the gudgeon pin out. Mine came out with mild resistance. If it is tight in there, it is advisable to by a tool for the job. Do not hit it with a drive and a hammer as this could bend the crank.
To fit the new piston it is just a reverse of what I just explained but ensure the arrow on the piston crown points to the exhaust. Use new gaskets at the base of the cylinder and also the head.
Whilst I had the engine out I replaced the engine mounts (silent blocks) and also the rear shock mount rubbers as they are cheap and I had never changed them before. I also replaced the rear shock for a new one as I'm pretty sure the one that was on was original from new so 48 years old. I also changed the front shock as that was definately dead. As the fuel tap was original and I could see some debris in the tank I elected to change that also. And you can see in the picture the tyre is worn, a new one was fitted.
With the engine back in the bike (sorry no pictures) the engine started no problem at all and even starts first time now. I have fit the new 20/20 carb and jetted it as a standard 150cc vespa and will adjust this accordingly as I ride.
Be mindful to run the new cylinder in, I will keep the revs low for around 150 miles and use a 3% two stroke oil mixture before I am confident of giving it a bit more stick.