Timing malfunctions: signs, causes and remedies

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:41

At the heart of any power unit and one of the main components of any internal combustion engine is a gas distribution mechanism. Its main function is to control the intake and exhaust valves. On the intake stroke, the intake valves open. The fuel mixture is fed into the combustion chambers. On the exhaust stroke, the exhaust valves open and exhaust gases are removed from the cylinder. This mechanism as a whole is quite reliable, if you follow the rules for operating the car. But sometimes it fails too. Let's look at the main timing malfunctions, their causes and repair methods.

Timing device

To begin with, let's briefly recall how these mechanisms work. On most engine models, the gas distribution mechanism consists of the following components and parts.

So, the valves are controlled by the camshaft. Most often it is made of steel or cast iron. It is installed in the crankcase. This crankcase covers the timing cover. Also on modern engines, the camshaft can be found incylinder head. As the shaft rotates, it acts on the cams, which in turn act on their valve.

The design also includes pushers - they are steel or cast iron. Their function is to transmit force from the camshaft and cams to the valves.

The mechanism has two valves - inlet and outlet. Their task is to supply the fuel mixture to the combustion chamber and then remove the exhaust gases. The valve is a rod with a flat head. The inlet and outlet elements are different from each other. The difference concerns the diameter of the head or cymbal. These timing elements are made of steel and heat-resistant steel (in the case of exhaust valves). The leg is a rod with a groove. It is needed in order to fix the springs. The valves can only move towards the bushings. To prevent oil from entering the cylinders, sealing caps are used. An outer and an inner spring are attached to each of the valves. The rods in the timing device are necessary to transfer the force from the pushers to the rocker.

The camshaft is driven by the drive. It can be chain or belt. The drive transmits rotation from the crankshaft. Distribution makes one revolution for two revolutions of the crankshaft - this is the engine duty cycle.

Possible malfunctions

Among the malfunctions of the timing, incomplete valve closure, excessive clearance between the valve stem and the toe of the rocker arms are distinguished. Gears, tappets, rods, rocker shafts, bearing bushings and camshaft journals also wear out.

Let's consider the causes and consequences of some typical breakdowns of this mechanism, as well as signs of timing failure.

Compression reduction

One of the symptoms of malfunctions is a decrease in engine compression and pops in the exhaust pipe. This happens after soot and shells form on the valve. Often the element can burn out. The cause of burnout lies in the loose fit of the intake and exhaust valves to their seats. Other factors also contribute to compression reduction. These are deformation of the cylinder head, broken or worn springs, jamming of the rod in the bushing, lack of space between the valve and the rocker.

Power reduction

Often, timing failures manifest themselves in the form of a decrease in power, in the form of tripling and metallic knocks. These are all signs that the valves are not opening fully. Part of the mixture of fuel and air does not enter the combustion chambers of the engine. Subsequently, the thermal gap increases, and hydraulic lifters fail. In fact, this is the reason for the malfunction of the mechanism and valves.

Belt or chain wear

This is one of the most common timing problems that happens especially often. In this case, the engine can completely fail. The drive belt breaks, and the pistons hit the valves that have not yet closed, as the camshaft no longer rotates. The reason lies in the wear of the belt or chain.

Timing Belt Troubleshooting

Damage of the drive belt leads tocatastrophic consequences, and this is a particularly frequent breakdown. Let's see the causes of timing belt failure.

So, most often the element fails due to a break in the straight cord. This may be due to the fact that the belt was broken before installation on the engine. The second reason is a break in the twisted cord.

This happens if there is any foreign body between the belt and the camshaft pulley. As a result, it cut deep into the rubber belt, and the cord broke. It can also happen if the installation is wrong. It happens that carelessness leads to this malfunction - the camshaft pulley could be rotated with a sharp screwdriver.

Tooth cutting

This happens because the belt tension is too low. Such a timing failure does not lead to catastrophic consequences, but the operation of the engine may be disrupted. The car may not start. Among the reasons, one can also single out jamming of the camshaft pulley, as well as intolerance.

Notches on belt teeth

This is due to excessively low tension. It also occurs due to loss of tension during operation.

Cracks in the back of the belt

Here, experts distinguish overheating of the belt, operation at low temperatures. In addition, a worn guide roller may be the cause.

Worn belt edges

If the belt is visually heavily worn from one of the edges, then there may be damage to the flangeor intolerance. In this case, it must be changed unambiguously.

Chain

For a long time it was believed that the chain is much more reliable than the belt drive. And this is true, but the chain is far from immortal. There are also malfunctions of the timing chain. If the belt breaks, then there is a small, but a chance to save the motor. In the case of an open circuit, the situation can be much worse. The chain is more massive than the belt, and if it breaks, it literally grinds the engine. Severe damage to valves and pistons occurs. In general, there is only one malfunction of the chain - it breaks.

Among the reasons is the quality of the oil. The chain resource is 250 thousand kilometers, but they rarely go for so long. Cases are widely known when the circuit in the engine broke off at a run of 100, as well as 60 thousand kilometers. But this is more often a factory defect in specific cars. Often, problems are associated not only with oil, but also with engineers' mistakes.

Signs of wear

A few symptoms will tell you about a worn chain. To avoid having to overhaul the engine (which is usually very expensive), it is necessary to change the chain as it stretches.

If the engine is idling rough and uneven, then the chain is already "fitting". This operation of the motor is due to the fact that the valve timing has changed. If the chain chirps at idle, then this is also one of the signs that irreparable malfunctions of the timing drive may soon occur.

If, after removing the cover, it is clear that the tensioner has reached its maximumdistance, if wear appears on the sprocket teeth, it is best to replace the chain.

Timing repair and maintenance

The main problem in this mechanism is worn journals, cams and increased clearance in the bearings. To reduce the gap, grinding of the camshaft journals is necessary. At the same time, the grooves for supplying oil are also deepened. The necks are ground to the repair size. Next, after repair, check the height of the cams.

There should not be even minimal damage on the bearing parts for the necks. There must be no cracks on the bearing housings. After cleaning and flushing the camshaft, be sure to check the gap between the necks and the hole in the cylinder head support.

The chain should not be stretched and have mechanical damage. As long as it is not worn out, it can be adjusted. Loosen the locking bolt half a turn. Then turn the crankshaft 2 turns and then tighten the locking bolt.

The rest of the timing troubleshooting is to replace worn parts. It is also necessary to periodically adjust the valves on vehicles that do not have hydraulic lifters.

Conclusion

As you can see, in the timing mechanism, the most popular problems are drive belts and chains. This is what professionals most often face during repairs. Other breakdowns are less common. But it is worth remembering that it is difficult to diagnose this node on your own - often the symptoms can correspondand other breakdowns. It is also worth remembering that most problems with the timing will lead to a violation of the distribution phases. And then you can start looking for the causes and ways to troubleshoot the timing. You can independently adjust the thermal clearances of the valves, and it is better to entrust everything else to specialists.