Simson awo sport, capacity 250 cc, year of production 1958.At the moment the piston behaves super. After grinding (grinding was done very precisely, in a professional workshop) the piston and rings do not generate any knocking, ringing or knocking. After the first firing I did not observe any swelling of the piston. It should be taken into account that lapping is done in stages and requires time, which is always in short supply, but for the moment I recommend :)