u have proberbly cracked/holed no3 piston, does it smoke when u start it?

had exactly the same on my s1 a few months ago so i took the bottom end out had it stripped and checked and had cracked no3 piston on the side and the rings also

so i had all the other parts checke and all i ended up needin was one piston a set of rings and a set of bearings and now have 175psi across all four cylinders