hi fellas
i have just acquired a spare barrell for wm20, it measures front to back half way down barrel 83.12mm and across the gudgein pin 82.86mm, is the sleeve ratshit or can it be rebored and to what size piston oversized 
email (option): markbro1@hotmail.com
Hi Mark...It looks like your cylinder is on +.040"(1mm).(standard bore size being 82mm) BSA pistons were made up to this size and then a new liner was fitted. Aftermarket pistons such as Hepolite went to +.060" (1.5mm) so you will need one of those or similar if the cylinder is in good enough condition to clean up at that size. Basically if there are no deep scores or serious rust pitting it should be OK for a rebore....Ian
email (option): ian@wright52.plus.com
Hi Mark..I would try Bantam John for an original +.060" if you do need a rebore. Also Russell motors may have something original.
The e bay piston is an Italian GPN..good quality but much heavier than the originals to the extent it will affect crankshaft balance...and a crankshaft balancing job is currently £80-100 plus shipping of the crank in both directions.
If you go down the new liner route, which would be a good plan if you have a good barrel and intend to keep the bike a long time and cover some miles, the liner will require boring to size after fitting...even for a standard piston.
The Draganfly piston works out expensive if you add up all the bits and pieces (£90 + postage + VAT? )...I hope it's a good quality one!...
As Rick says it is worth taking a really good look at you original bore to determine whether it will 'go again'...If you think it might,clean it up and get it carefully measured at an engine shop if you don't have bore gauges/micrometers yourself. This depends rather on what your plans are for the bike..it could certainly keep you going for some time if you don't rack up a high mileage. If you do you will have the same problem again later when parts are likely to be even less available...Ian
email (option): ian@wright52.plus.com