Todays materials and engines are produced in small tolerances that there is no issue with fitting the materials. The only thing what realy happens is when cooling down there is a little bit grow in the piston.
When running in with the heatcycle the grow will taken care of with the next tank and at the end the piston will be a tiny bit looser than when going to run it in all the way without stopping. If you do that it will take a while when the piston becomes realy loose.