How to judge the piston knocking?

Oil by cylinder. The position of the cylinder is determined by the method of cutting the oil by cylinder. If the oil is broken to a certain cylinder, the sound is obviously reduced or disappeared, and the "click" can be heard when the oil supply is restored, indicating that the cylinder piston knocks.

In order to further verify the cylinder piston knockout, the injector of the cylinder can be unloaded and a small amount of CD medium engine oil is added to the cylinder, and then the injector is installed, the engine is launched, the knocking sound is disappeared or weakened, and the rapping sound appears again for a moment, then the cylinder piston knockout is no doubt.