Engine knocking, what to do and how to determine the cause?

During operation, an automobile engine requires periodic intervention in the form of maintenance, as well as scheduled and unscheduled repairs. Along with a huge list of problems, “knocking” engines began to appear more and more often, even without having time to work out the prescribed mileage.

So, why the engine starts knocking, how to find and solve the problem of extraneous sounds - read on.

Engine knock diagnostics

The most responsible and difficult part before repair is to make a competent diagnosis. An internal combustion engine is a complex unit in which there is a mass of rubbing parts, as well as mechanisms with rotational and rotational-translational movements. Based on this, the diagnosis of knocking in the engine becomes more complicated, however, with the help of special devices it will be possible, if not exactly, then approximately to find out the source of extraneous sound.

Engine diagnostics for sound should be carried out according to 3 parameters:

1. What is the nature of the sound: episodic, rare or constant - the dependence occurs on the degree of operation or wear of individual mechanisms.
2. What is the tonality of the sound. This is a crucial and difficult moment to determine the accuracy of the sound being emitted. Only an experienced specialist understands that a thin and sonorous sound on different engines can mean one malfunction, which lies in the wear of the crankshaft bearing. Depending on the design of the internal combustion engine, a different nature of the sound can mean the same malfunction.
3. Localization. To determine the location, a stethoscope is used, which will direct the master to the approximate area of ​​the sound being emitted.

Reasons for knocking the internal combustion engine

There can be a lot of reasons why the operation of the engine is accompanied - from the most outstanding, in the form of an untimely oil change, to exceeding the warranty motor resource of the power unit. Consider all the options in which a knock, clatter, rattle and other extraneous engine sounds can occur, as well as diagnostic methods.

Immediately, before identifying possible causes, let us turn to the theory of ICE design. 

The piston motor has key assemblies and details:

• cylinder-piston group - constant work takes place here, accompanying 4 cycles (intake, compression, stroke and exhaust);
• the crank mechanism is a crankshaft with connecting rods and a flywheel. This mechanism pushes the pistons, and from them it receives mechanical energy, which is transmitted to the flywheel;
• gas distribution mechanism - consists of a camshaft with a star and a gear, as well as a valve mechanism. The camshaft is synchronized with the crankshaft by means of a belt, chain or gear, cams, through a rocker arm or a hydraulic compensator, it presses on the intake and exhaust valves, through which fuel and air enter and exhaust gases exit.

All of the above details are in constant motion, which means they are potential sources of all kinds of unnecessary sounds. 

How to listen to engine knocks?

Experts use a stethoscope to determine the nature of the extraneous sound and its localization. For self-listening, you can make a device yourself, but the time spent will be directly proportional to the cost of diagnostics in a car service or the purchase of a budget stethoscope. By the way, some service stations have electronic stethoscopes in stock, which indicate 99.9% of the exact place of sound origin.

Speaking of tonality, in a small car and a V-shaped "eight", the first sound of wear of the main bearings will be clear, in contrast to the second. Often, the design features of the internal combustion engine are the reasons for all sorts of unnecessary sounds.

The knock emitted from the motor can be constant, intermittent and episodic. As a rule, the knock is associated with the revolutions of the crankshaft, and the faster it rotates, the more intense the knock.

The sound may change depending on the degree of load on the engine, for example, at idle, a slight tapping, and on the go, at a speed of 30 km / h and the inclusion of 5th gear, the load on the engine is strong, respectively, the knock may appear more distinctly. It also happens that a strong knock is heard on a cold engine, and disappears when it reaches the operating temperature.

Engine knocking at idle

This phenomenon occurs only at idle, and when the revs increase, extraneous sounds disappear. There is no cause for serious concern, but the problem cannot be avoided. About the reasons:

• something touches the crankshaft pulley and pump;
• poorly fixed engine protection or timing case;
• on motors with a gear-type timing belt there is gear play;
•  loosening the crankshaft pulley bolt.

If the pistons knock

During operation, the clearance between the cylinder and the piston gradually increases. The manufacturer has deduced the specified parameters of the standard clearance, exceeding which leads not only to knocking, but also oil consumption, a decrease in power and an increase in fuel consumption.

If piston fingers knock

The knock of the piston fingers is ringing and clattering. The sound can be clearly heard with a sharp set of revolutions of the crankshaft or a sharp release of the "gas". The phenomenon occurs when the gap is increased by more than 0,1 mm. For diagnostics, you need to unscrew the spark plug and turn the engine. 

Often, the clatter of fingers is accompanied by detonation, as well as movement at low speed in high gear (as they like to ride on diesel engines). 

Knocking crankshaft bearings

The wear of the liners is accompanied by a dull sound that does not change in all operating modes of the internal combustion engine. Along with this, the oil pressure drops, which is “lost” between the increased clearance between the liner and the crankshaft journal.

If the mileage of the engine does not provide for wear on the liners, it is recommended to replace the engine oil with a thicker one with the necessary additive package, then listen to the engine. This helps in many cases. 

Knocking of connecting rods

In many cases, wear in the connecting rod bushings is accompanied by a strong knock, and only replacing the bushings with a preliminary defect of the crankshaft will help here.

If we neglect the timely repair, that is, the option of detaching the connecting rod journal, and this is damage to the crankshaft, breakdown of the pallet, and possibly failure of the entire cylinder block.

By the way, if the problem was not in the connecting rod bearings, then it lies in insufficient oil pressure, which is accompanied by two factors: liquid oil and wear of the oil pump gears.

Noises in the gas distribution mechanism

A fairly common phenomenon is extraneous sounds coming from the timing. Diagnostics is carried out when the valve cover is removed, the rocker (rocker arm) or hydraulic lifters are carefully examined, the valve clearance is checked, and the condition of the camshaft cams is studied.

The first step is to set the valve clearances, after which the motor is checked for extraneous sounds. If the motor is equipped with compensators, then they are washed, checked for operability, and after installation, the oil is changed. If the "hydraulics" are in good order, then the timing belt will work properly. 

Among other things, the reasons may lie in the following:

• wear of the camshaft cam;
• increased clearance between the pusher and the cam;
• wear of the end of the timing valve;
• wear of the adjusting washers.

The problem of knocks and noises in the timing area should be immediately paid attention, otherwise there is a risk of the piston hitting the valve, or vice versa - the valve is clamped and the compression in the cylinder drops.

The most famous "knocking" motors

One of the most famous engines is the 1.6-liter CFNA unit, which is installed on the cars of the VAG concern. It is a chain motor with 16 valves and a phase shifter mechanism.

The main problem is that the “cold” pistons knock until the operating temperature is reached. The manufacturer recognized this as a design feature of the cylinder-piston group. 

Renault's DCi diesel engine series is famous for its weak crank mechanism. Because of this, overheating, overloading and untimely oil change will lead to the fact that before reaching 100 km, the engine will fail.

The weakest engine in the lineup was the 1,5 liter K9K diesel. Some call it experimental, because it "suffers" from turning the liners already to 150 thousand km.  

Engine Repair Tips

Overhaul of the engine involves the replacement of key engine elements: pistons with rings, liners and comprehensive cylinder head maintenance with the possible replacement of valve guides and cutting the seats. Top tips:

• always check the cylinders of the cylinder block for an ellipse;
• choose pistons and rings of the highest quality, because this is enough for more than 200 km;
• the size of the liners should be selected after accurately measuring the crankshaft journals, the connecting rod journal bolts must be checked for tension;
• assembly of the motor must be accompanied by the use of assembly paste or lubrication of rubbing surfaces in order to exclude a “dry” start;
• use only the oil that meets the mileage and requirements of the car manufacturer.

Questions and answers:

How to understand what is knocking on the engine? Pistons, piston pins, valves, hydraulic lifters, crankshaft or parts of the piston group can knock on the engine. Pistons can knock on a cold one. At idle, vibrate the timing case, generator pulley or pump.

Can I drive a car if the engine knocks? In any case, the knocking on the motor is unnatural, so you need to diagnose the cause. In this case, the engine must be warmed up before driving.

What's knocking on a cold engine? Large clearance between piston and cylinder wall. Aluminum pistons expand strongly when heated, so the knock in such an internal combustion engine disappears after warming up.