Basingstoke_Scooter_Club » Page 14 of 18

This is not a good outcome – every scratch will become a key to future carbon deposits and could encourage ‘hot spots’ inside the head and strange engine running problems in the future. Scrape Aluminium with aluminium. If you have no aluminium try substituting hard wood or plastic scrapers. The best way forward is possibly to use a brass wire brush (not a steel one!). Small versions of these are easily and cheaply available. If you want a sparkling finish, try wet and dry medium grit, but don’t mark the mating surface of the cylinder head. Remember, the Vespa does not use a cylinder head gasket and the mating surface must have no scratches or blemishes? Some go even further and polish the inside of the combustion chamber with metal polish – this looks nice, if nothing else!

The top of the piston, known as the crown, next requires attention. By depressing the kick-start lever raise the piston to top dead centre. Scrape the carbon off in a similar manner as you did to the head, with the same rules applying as to scratching the soft aluminium crown. Carefully clean off any loose carbon debris from around the mating surfaces of the cylinder head and the piston crown, being very careful that none of this escapes down the machined face of the bore. A difficult act if the piston is at the top of its stroke!

Reassembly of the engine is the reverse of the strip down. Tighten the cylinder head nuts gradually. Tighten the nuts diagonally opposite each other as you go and the head will snug down, nicely. A thin smear of mastic around the exhaust stub and matching section of the silencer down pipe helps to seal the exhaust. Any sort of mastic will do, don’t waste money on exhaust sealing mastic, it’s a con!

Finally, as always, double-check the wheel nuts for tightness when the rear wheel is in place. That can be a real lifesaver!

Some folk get in a hell of a state locating the washers and nuts for the cylinder head onto the studs on reassembly. Just slide, firstly, the cylinder head nuts, then the spring washer and, finally, the flat washer onto the shaft of a screwdriver. If the blade of the screwdriver is now lined up with the end of the stud, the nuts and washers can be slid down the screwdriver shaft and spun into position with the fingers. Easy job!