I remember long ago when I worked at a dealership my brother was a mechanic also. A customer bought a new duster with a 318 engine and it came in with a misfire on # 7 cylinder he replaced the spark plug and it was fine for a couple thousand miles and came back with a misfire so he did a compression and cylinder leak test and found it was low and going past the piston. So he tore the engine down and found to his surprise no rings on the piston
