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1975 250 Desmo

I was looking to fix an oil leak from the cylinder head, thinking that the o-ring between the head and barrel had perished. There was also oil at the end of the exhaust pipe.
Right, so off with her head, so to speak.
The o-ring had indeed hardened, but I took off the barrel while I could, and found that the top piston ring had corroded with the barrel, creating a groove large enough to pass oil.
No problem, a rebore will fix it - except that this turns out to be a 239cm3 engine.
Am I right in believing the barrel can be bored to take a standard 74mm piston?
There are some pistons available for various 250 models, were they all the same, or are they model specific?
Appreciate any advice, thanks.

It is possible to bore out a 239 cylinder to 250, it just takes a few more cuts.
As regards pistons, there is quite a choice, although finding standard size 74mm pistons is a bit harder than finding oversize ones.
Most of the pistons for sale are high quality forged items, being sold at a high price.
Years ago, Meteor pistons were available. They do still occasionally come up for sale. While they are usable for a road bike, they are of poorer quality and are a cast piston.
I think the Vossner pistons made in Germany are machined from solid billet. They do however come with an odd size of piston ring ( 1mm, 0.8mm and 2mm scraper ) which may make ring replacement difficult in the future.
The choice is yours. It's still going to be expensive.

If anyone wants a set of replacement 239 rings, for a 72.5 bore, I still have a couple of sets available. They are quite hard to get hold of if you need a set.

Jon

Thanks Jon.
I think I'll go for one of Nigel L.'s Omega forged pistons.
As you say, standard bore size (74mm) isn't easy to find.