Fr...since no one is replying...yes...usually .002" is about right for a street engine. Some builders go a bit looser on a race engine. Depends on the bore size. Typically the larger the bore, the larger the clearance...within reason. This compensates for the greater expansion of larger pistons.
I do the same thing when I get Pistons made. They recommend .002".
Did you mean "ART" pistons? They are good pieces...OEM supplier to Honda. Should be able to run .002- .0025 no problems. (Measured at the skirt perpendicular to the pin).
I recommend Langcourt Cylinder Technologies in Georgia. About a 5 day turn around not including shipping. Usually under $100 to get a twin bored. Excellent work. You get the cylinder back cleaned to perfection, and stamped with a serial number. Send them the pistons and they'll do the measuring.
Yeah, ay are tee, not dee. Couldn't remember, got 'em on ebay for too much, but I needed 'em before Xmas, to send down with my bro to give to another bro who's been a machinist since he was old enough to take apart my mom's Waring Blender. So I got the family connexion, but thanks for the tip anyhow. And I'm glad to know ART is legit, 'cause I'd never heard of 'em.
I think you're right, by the way, going back to a way previous discussion, about picking a specific bike to race and developing it to the extent that you can. I don't mind learning new stuff, but finding new vendors etc for different brands and seeking out the answers for some of this old crap can add more time and money to a project than it may be worth.
If I was doing this on an SR/XT/TT500 I'd have all the parts I need, at least as far as engine/frame, in my hands right now.
'Course, if this 450 turns out to be competitive, I guess I'll be singing another tune, but I have my doubts about how good a racer it'll be.