A stethoscope helps to localize the source of extraneous noise.
Often, even inexperienced drivers begin to distinguish some extraneous noise from the usual sounds of the car, which was not there before. In such cases, it is best to consult a guru, and he can bring to the aid of a simple device – a stethoscope.
This device is similar to a medical device with which a doctor listens to your heart and lungs, but instead of a soft plastic membrane pressed against the body, in a technical stethoscope the sound is “removed” by a thin metal rod – a probe that already transmits vibrations to the membrane.
An experienced mechanic with its help localizes the source of a suspicious sound more accurately.
A technical stethoscope costs 500-2000 rubles. In most cases, we have to listen to the noise of rotating units. It is important that the dipstick does not come into contact with rotating parts, because it can be pulled under, for example, a drive belt or even a timing belt.
What can you listen to?
The richest source of noise is the engine. Inside it, many parts perform reciprocating and rotational motion, and many auxiliary units rotate outside.
However, in the gearbox at idle, you can also hear something curious. And if you turn on the gear and climb under the car hung on the lift, you can listen to other transmission units. On all-wheel drive vehicles, this is a transfer case, gearboxes and outboard bearings of the driveshaft. You can try to determine the malfunction of the wheel bearings, but they make a clear sound only with significant damage to the treadmills and rolling elements.
Unfortunately, a stethoscope is unlikely to help in determining the malfunction of CV joints and crosses. You can press the probe only against a fixed body part, the sound of which comes from a damaged bearing, gearing or backlash assembly (for example, a phase shifter).
There are five main listening zones in the mechanical part of the engine. These are the zones of the main and connecting rod bearings, the piston group, valves and camshafts, as well as the timing drive, if it is carried out by a chain or gears. The camshaft belt drive should be considered separately. [I], [II].
Noise zones heard on the surface of the basic parts of the engine: 1 – valves and camshafts, 2 – timing chain drive, 3 – piston group, 4 – connecting rod bearings, 5 – main bearings.Timing chain drive noise listening zones: 1 – intake camshaft phase shifter, 2 – tensioner and damper zone.
Timing belt drive
Here you can listen to the sounds [III]emitted by the phase shifters of one or both camshafts, idler and bypass rollers and, in some cases, the coolant pump.
The coolant pump can be rotated by the timing belt or the accessory drive belt. Its failure is more dangerous in the first case. But climbing to a pump driven by a toothed belt is, unlike, more dangerous – both for the performer and for the motor. And for many engines, an attempt to expose the timing belt on a running engine rests on the fact that the engine is deprived of the right support of the power unit and needs to be supported from below or suspended.
Timing belt listening zones: 1 – tension roller; 2 – bypass roller; 3 – phase shifter (its noise can be heard by leaning the stethoscope probe against the camshaft bearing cap).
There are several main areas for listening with a stethoscope. [IV] The bearing may hum at the generator, but with severe wear, the hum can turn into a rattle.
In the air conditioning compressor, the bearing can also rattle. [V], regardless of whether the air conditioner is on or not. If the noise is heard with a roar when the air conditioner is turned on, it is a serious matter, you need to go to the service.
The idler pulley can also make a hum. In the event of a malfunction, the power steering pump starts to make noise, when the steering wheel is turned, a hum, whistle, squeal, or even rattle appears.
A great effect from a stethoscope can be obtained when checking auxiliary units: 1 – air conditioning compressor, 2 – generator, 3 – tension roller, 4 – power steering pump.By pressing the probe of the stethoscope to the fork acting on the clutch release bearing, you can hear its noises.
In mechanical gearboxes, hum may appear, for example, due to wear of bearings, shaft gears, springs on the wings, differential. Automatic transmissions most often hum due to low oil levels, as well as problems with the torque converter and lever rocker.
All-wheel drive transmission of an SUV with a rigid connection of the front axle. Listening places: 1 – gearbox, 2 – transfer case, 3 – front axle gearbox, 4 – rear axle gearbox.
If the cardan shaft line is equipped with an outboard bearing, then with the help of a stethoscope its “complaints” will be clearly audible. Angle gearboxes containing a hypoid gear, with significant damage to the gears, are heard very well.
The rear axle couplings can be electromagnetic, and then only damage to the bearings is heard, but they can contain pumps, and then their damage causes the corresponding sound.
The all-wheel drive transmission of a modern crossover can be heard at several points with the engine running and the gear engaged: 1 – gearbox, 2 – bevel gear, 3 – propeller shaft outboard bearing, 4 – rear axle drive clutch, 5 – rear axle gearbox.
Will the newbie do it?
At the first attempt to single out the harmful one among the general noises, a beginner may not succeed. In some cases, it is desirable to listen to a “symmetrical” node and compare the results – for example, if you suspect wheel bearings, you need to compare the noise of the left and right. You can listen to a similar unit on another car – not necessarily exactly the same. So you can gain at least a minimum experience.
How to save on car maintenance and not regret it later is described here. “Driving” can be read in Viber