Yeah, I was off by a decimal point, there is between 0.0030" and 0.0029" clearance.
If they are really those numbers, that's a bit looser than the normal recommendations of 0.0018"-0.0022" for the forged-type pistons from JE or Wiseco. If they are the more common cast pistons, like from Honda or ART, the clearance should be half that much, at 0.0010" (0.0008-0.0012", to be precise).
The reasoning: the forged pistons cool slower (and heat slower) than the cylinders around them. So, during startup, they will sometimes rattle a bit and might even burn a small amount of oil until they warm up enough to seal the bores well, very common. And, they are more warmup sensitive as the result. The cylinders conversely cool faster around them when the engine is shut off. The extra 0.001" typical clearance helps keep them from sticking in the bores (on their skirts) if the rider is, say, commuting around town, stopping at stores, jumping back on the bike, etc.
When the piston material more closely matches the cylinder fins' metals, this heating-cooling cycle difference is not so pronounced.
Racers learn that the forged pistons can withstand more power (i.e., hotter fuels, spark advance, compression, etc.), but only if they are bored "tight" like the regular pistons, all else being equal, Winning racers also know that a full cooldown is required before a restart in these 'tight' engines, or trouble develops pretty quickly. Pit crews I knew often had generators running big fans to cool off these engines during pit stops after the "no running while fueling" rules occurred in the 1970s.
So, in these engines it is a decision of "balance" between the clearance and the riding style: machine shops who don't know the customer will often tend to the looser side so they don't get blamed for a stuck piston later. If it is a little looser (as this appears to be), then always run the 20w50 oils to help keep the piston skirts heat transfer up with the cylinder walls and it should work out OK.
Another way to "check" although a bit hard to find, get some feeler gages of .001", 0.0015" and 0.002", lay one in the bore, slide the piston in over it and see what the clearance is on the wide part of the skirt (90 degrees from the pin). If the gage slides out snugly, that's the one. If it sticks, that's the thick one. If it slides out easily, it's bigger than that. This isn't the best way to measure things when boring, but it is a decent shade-tree wrench's check.
