WARNING: If you have any doubts about diagnosing the problem yourself, get out the tow rope. A major repair to a damaged engine will cost more than a towing service.
Knocking of main bearings can be heard at the very bottom of the cylinder block - very dangerous; stop the engine immediately, you will have to go to a car service or garage by tow. Low-pitched knocking, noticeably increasing under load and with an increase in crankshaft speed. Often its appearance is accompanied by a drop in oil pressure (the oil pressure warning light is on almost constantly).
Knocking of connecting rod bearings can be heard in the middle part of the cylinder block - very dangerous; stop the engine immediately, you will have to tow it to a car service or garage. The sound is rhythmic, ringing, metallic, medium tone. It increases significantly with increasing load and completely disappears when the spark plug is disconnected.
Knocking of piston pins can be heard in the upper part of the cylinder block - dangerous; without loading the engine, you can drive to the car service or garage on your own. The sound is rhythmic, high-pitched with a sharp metallic tint, audible in all engine operating modes and increases with increasing engine load. It disappears completely when the spark plug is disconnected.
Knocking of worn pistons and cylinders can be heard in the same part of the engine as the knocking of piston pins - not dangerous; without putting too much load on the engine, you can drive to the car service or garage yourself. A sound reminiscent of the clatter of clay pottery. It is especially audible on an unheated engine, and decreases or disappears as it warms up.
Valve knocking can be heard in the upper part of the engine in the area of the cylinder head cover - not dangerous, you can drive to the car service or garage yourself. Metallic knocking against the background of a general dull noise. Can be heard well at low and medium crankshaft speeds from the side of the cylinder head above the valve locations.
Detonation knocks - dangerous, but usually eliminated by replacing the knock sensor or filling with good quality fuel. Avoiding heavy engine load, you can drive to a car service or garage yourself. Ringing metallic knocks that usually occur when accelerating the car. Cause - failure of the knock sensor, use of low-octane fuel, engine overload when switching on a higher gear too early, significant carbon formation in the combustion chambers. It is necessary to use a special fuel additive to remove carbon deposits on the valves and in the combustion chambers.
(The original article is on the website: ChevyMan)