I will beg to differ with you in some respect. My experience, at least with car engines, is that a wise machinist will carefully measure each piston, and then prepare the cylinder bore accordingly. There are almost always some differences in piston diameters, even if bought in a set.
Ask me how I know... I had to remove a vintage Cadillac V8 a second time and disassemble because the first machine shop just used factory specs rather than measuring the pistons and boring the cylinders to match. First time we started it up, it ran for 30 seconds then quit as the pistons expanded. That cost me a whole new set of pistons, and another machine shop!
We always have to learn these things the hard way.
If anyone happens to have the recommended piston-to-cylinder clearances (either original Ariel or Drags) I'd appreciate having those numbers.
Phil Auldridge Austin, Texas - USA
Visit the North America Ariel forum: http://arielnorthamerica.org/phpBB3/
53 SQ 4 MK II, '72 Norton Commando, '78 BMW R100/7, '79 Honda CBX, 2014 Indian Chief Vintage