1) your bearing broken down already and some small fragments come from bearing to the cumbustion chamber
2) they are residues from manufacturing process but the manufacturer didnt clean it completely
How many tanks u have played already? U shall dissemble your engine completely and use fuel to clean it completely...and check the bearing by using finger to rotate the inner ring...if u feel gap movement from the bearing...u have to replace the bearing with new one...if ok, then go to play play....if u find the performance is still no good, u may need to replace cylinder and piston na