Scooterotica

I asked AF Rayspeed if it was ok to use a 225 barrel in a casing reamed out for a 250 barrel. "Yes it's fine".

But is it really?

I took these pictures earlier to show the gaps between barrel and casing. I know they would idealy need matching, but the gap is what concerns me.

Opinions would be greatly appreciated. The idea of getting the whole mouth redone to normal spigot size scares me with what it would cost.

I share your concerns. If the barrel is not properly located when the piston is wazzing up and down 6000 times a minute your engine, or you could get hurt!
Revert to 250 top end or do an exchange for an standard casing. I'm sure someone (on here?) would like to go large.

SF

i've got a rapido 250 and was wondering about putting a barrell back on with a standard spigot at some point,a 225 has quite a thin spigot,whereas a 200 has a more substantial spigot,does the casing need to support the spigot o rdoes it support itself.

I would dowel it, barrel to casing. The spigot is plenty thick enough i reckon....

The strength of the spigot isn't the issue. The accurate position of the barrel in relation to the crankshaft is. It's important. Innocenti and SIL machined the spigot dia and crankcase to ensure that relationship is correct.
When AF open out the crankcase to accept the bigger liner of the 250 then the relative postions as lambretta intended are maintained so all is good. BUT when you revert to a standard barrell its a p155 fit in the casing and you are relying on the studs to position the barrel. They are not intended to do that. They 'just' hold it all together.
If the barrel is off centre to the crank you will use up the designed clearances between piston & con-rod and con-rod and flywheel. That's going to cause increased friction & wear at best and a trip down the tarmac at worst.

SF

Thanks for the info.