Warning! If you have the slightest doubt about self-diagnosis, get out the tow rope. Serious repairs will cost more than the towing service.
Engine knock listening zones:
1. Knocking of main bearings - very dangerous; stop engine immediately, we are towing to the car service. Low-pitched knocking. It is heard in the lower part of the crankcase, noticeably increases under load and with an increase in rotation speed. Often its appearance is accompanied by a drop in oil pressure (the oil pressure drop light is on almost constantly).
2. Knocking of connecting rod bearings - very dangerous; stop engine immediately, we are towing to the car service. The sound is rhythmic, ringing, metallic, medium tone. It increases significantly with increasing load and completely disappears when the spark plug is disconnected.
3. Knocking of piston pins - dangerous; without loading the engine, we go to the car service ourselves. Rhythmic, high-pitched with a sharp metallic tint, audible in all engine operating modes and increases with increasing engine load. Completely disappears when the spark plug is disconnected.
4. Knocking of worn pistons and cylinders - not dangerous; avoiding overloading the engine, we go to the car service ourselves. The sound resembles the knocking of clay dishes. It is especially well heard on an unheated engine, as it warms up it decreases or disappears.
5. Detonation knocks - dangerous, but, as a rule, are eliminated by setting a later ignition. Avoiding a strong load on the engine, we go to the car service ourselves. Ringing metallic knocks, which usually occur when accelerating the car. The reason is an incorrect ignition setting, the 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 contact a car service to adjust the ignition and use a special fuel additive to remove carbon deposits on the valves and in the combustion chambers.
6. Valve knocking - not dangerous, we go to the car service ourselves. Metallic knocking against the background of a general dull noise. It is clearly heard at low and medium crankshaft speeds from the cylinder head side above the valve locations. Valve knocking is often confused with tappet knocking (the last one is very high-pitched and variable in volume, practically unavoidable).
Knocking in suspension and transmission
Warning! Faults in the vehicle's suspension and steering can lead to a serious accident!
If extraneous knocking sounds appear in the suspension of a moving vehicle, it is necessary to immediately determine their source, regardless of whether the knocking is constant or appears only when driving over uneven surfaces.
Check the condition of the suspension it is better to place the car on a ramp, inspection ditch or lift, and if this is not possible, you can do this work on a free level area, although with less convenience. In any case, you will need an assistant.
1. Start with a careful inspection of the suspension components. Pay attention to the condition of the rubber protective covers of the ball joints of the front suspension. Ruptures and cracks in the covers are unacceptable, since in this case moisture and dirt get into the joint, which leads to premature wear of the joint. Replace damaged parts without fail.
2. Check the condition of the rubber-metal hinges and rubber bushings of the lower arms, stabilizer and stretchers.
The photo shows the right side of the car. On the left side, check the same places by analogy.
3. Open the hood, remove the plastic protective caps from the upper supports of the telescopic struts and check the condition of the upper support. There should be no cracks, tears, swelling, etc. on the rubber part of the support. After a preliminary inspection, you can proceed to a more detailed check.
4. Ask an assistant to grab the top of the front wheel of a car parked on the road with both hands and shake it sharply in the transverse direction. At the same time, you should observe the presence of gaps in the front suspension joints. Pay special attention to the ball joint.
Tip: It is easier to determine the presence of a gap (play) in the ball joint if you touch the ball joint with your hand while rocking the wheel.
Are there any gaps in the suspension joints?
No: see point 6.
5. Worn joints require replacement.
6. Check the tightness of the nut securing the shock absorber rod to the upper support of the strut.
7. Jack up the car on the side being checked until the wheel is off the road. Place a strong support (tripod) under the body sill and lower the car slightly to load the support. Rock the wheel in a vertical plane, holding the top with one hand and the bottom with the other.
Increased knocking from the central part of the wheel indicates a large gap in the hub bearing. It is better to entrust the replacement of a worn bearing to specialists who have the necessary equipment.
Warning! Do not give in to the persuasion of "experts" who recommend tightening the hub nut with a force higher than recommended by the manufacturer to eliminate gaps. This may lead to the destruction of the bearing.
8. Inspect the telescopic suspension strut. Oil leaks indicate a faulty shock absorber. In this case, the shock absorber requires repair or replacement. Check the integrity of the spring and compression buffer.
9. Check the brackets that secure the struts to the car body. The brackets should be securely bolted to the car body and not damaged.
10. When checking the rear suspension, pay attention to the condition of the hub bearings, shock absorbers, springs, bump stops and the fastening of the shock absorber rods to the body.
11. You can tighten the shock absorber rod nuts from the luggage compartment, after removing the seat belt reels and trim.
Advice: After replacing individual suspension parts, be sure to check and adjust the front wheel alignment angles. This operation should be carried out on a special stand in a car service center, since incorrect wheel alignment leads to accelerated tire wear, increased fuel consumption, and deterioration in vehicle stability and control.
Recommendations
Pay attention to the exhaust system. Very often, due to the use of non-standard elements or a break in the muffler suspension elements, it can be the source of a strong knock, especially when revving. To check, stop the engine, carefully inspect the exhaust system, check the reliability of the fastening and suspension of the muffler. Taking the end of the exhaust pipe, swing the muffler up and down and from side to side - there should be no knocking.
Knocking in the suspension is often confused with knocking in the constant velocity joints (CV joints) of the drive axle shafts. The sound is a ringing metallic clicking, especially evident when the accelerator pedal is pressed sharply with the front wheels turned at a large angle. As the CV joints wear out, the duration of the clicking increases. The only radical way to combat the knocking of CV joints is to replace them.
(The article is taken from the website: «VAZbook»)