I had a Polini 208 cylinder rebored ( Asso Vertex 2 ring piston) and was advised by Taffspeed to get 0.09mm bore clearance, did that and got the bike dyno'd. Ran it very gently ( max speed 45 miles per hour ) for 450 miles and got a small seize for my efforts , so I then ran it very very gently for another 250 miles ( thats 700 miles total) and got another seize at 55mph, then ran it at breaking in pace for another 400 miles ( thats 1100 miles in total  ) and figured it must be fully ready to go now so opened the throttle and let rip , did 5 or 6 miles at 70 - 75 mph , and then was cruising at 62 +/- mph when it seized really hard with no warning. It took all my riding experience to stay on , and after a little sideways speedway stunts I managed to stop without hitting any of the other traffic -I was really lucky. [8o|]
18 degree timing, fully synthetic pre mix , 24mm carb with 3mm spacer and DRT float chamber conversion , B8es plug with .55 gap, Sitoplus exhaust , 125 main jet ( set by Taffspeed at the Dyno run and told me it was still rich).
The piston has seize marks all the way round below the rings, and the plug is a very nice light chocolate brown colour. Piston crown is undamaged.
I think this is purely down to the rebore being too tight, I have honed the barrel and even after this there is still only 0.23mm piston clearance.
Any suggestions as to what the correct rebore / reuse clearance should be as I have no wish to try that trick again ?