Scooterotica

I've got a casing converted to run a 250 rapido or RB.........can I run a standard 200 or 225 top end on it? cheers

No reason why not, the primary compression might be a bit lower that usual but that's not always a bad thing and you will have to play about with base / head packers to adjust the barrel height but others will be along with more detailed advice

Is this the case conversion where the spigot mouth is machined larger? If this is the case I think it is a one-way trip.

Yeah the casing is opened out as the 250 rapido and RB gave a thicker spigot , my thoughts were that once done it was only good for 250 cylinders but thought I'd ask on the off chance! cheers

You can use the casing when the mouth has been enlarged for a 72 mm spigot, its not a problem, I did it for a few 1000 miles and now my mate has the engine done loads of miles no problem.

Does the spigot not come in to play regarding centralising the barrel.surely a larger case mouth will let the barrel move when fitting ?

Could the spigot be sleeved ?

Wouldn't have thought it was an expensive job and would give an option for useable cylinders....

i was thinking of a sleeve, but it would be in the way of the tranfers, i think the best option would be to make some small dowels to go over the barrel studs, yo might be able to find some steel tube with the correct inside diameter to be a snug fit on the studs, you will only need 10mm lengths, slide down the studs to the bottom, you will then have to open up the stud holes in the barrel ,only deep enought for the dowels,so its a snug fit, job done, you barrel will be centralised and supported

The bottom line is.....it's not ideal, but it's not the end of the world.

In Lambretta engine building there are wildly varying standards of quality. You could obsess about the spigot not being a correct fit......whilst neglecting to acknowledge that the ports have no chamfer, the ring gap is too tight, and the bore is all-to-cock.....or you might set your comp ratio, or squish, or ignition timing all wrong and hole a piston.

So it's all relative.

If you are building a 'serious' engine, with big power, intended for lots of miles.....maybe try a different set of casings. But if it's a cheap n cheerful 'local blat around' engine...........


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Thanks for the replies guys, it's just a spare casing I have so think I'll punt it on , unless anyone will sell me a rapido 250 cylinder lol