2-stroke engines with non-roller bearing con-rods need quite a bit of play to allow lubrication.

I reckon 5-20 thou up and down on the big end is ok, provided you dont advance the ignition above 30 degrees - you wont knock/damage it much

what the spec says i dont know, but 2 running engines had 10 and 20 thou without knocking - thats a fact

the little end should have almost no play and be a sliding fit with the piston pin, i guess 5 thou wont hurt.

LATER engines seemed to have a roller bearing con-rod - nice if you can find one - no play on these, so should run quieter?

Note the crank is HQ steel and not prone to much if any rusting.