BSA oversizes usually went to +.040"....Many of the barrels will take more than that, in some cases a lot more...The B33 for example can be bored out to 90mm from its original 85mm bore size without any issues...After market manufacturers back in the day provided pistons for many BSA models up to +.060" to give that extra rebore that extended the barrels life...So, in the case of your bike I would imagine +.060" wouldn't present any problems....Ian
Many thanks Ian,
Good to know that +40 thou should be safe. Bore looks to be in good condition but I will get it measured when the engineering shops re open and hopefully it will be reusable with just a light hone and the correct size piston.
