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Bent valve: what is the reason and what to do about it
Bent valve: what is the reason and what to do about it

Sometimes cars give owners a lot of problems. One of the worst failures is bent valves. This happens when the timing belt breaks. After a break, the valves completely fail. Let's look into the causes, as well as learn how to prevent and repair.

Why do engines need valves?

First you need to study the theory. Probably, every motorist knows the number of cylinders in the engine of his car, but not everyone can answer the question about the number of valves. Most modern internal combustion engines can have from 8 to 16 valves. There are such power units, where there can be 24 or more. The valve is an important part of the gas distribution mechanism of the engine. He is responsible for supplying the fuel mixture to the combustion chamber and for the exit of exhaust gases into the exhaust system. Each cylinder has two valves: one inlet, the second - exhaust. In 16-valve engines, there are four valves for each cylinder if the engine is four-cylinder. There are also engines where there are more intake elements than exhaust ones. These are three- and five-cylinder engines.

bent vaz valve

The valve consists of two parts - a plate and a stem. It is the rod that gets hit when the timing belt breaks. The valves are driven by the action of the camshaft on them. He, rotating around his axis in the cylinder head, can raise and lower the valves.

The camshaft is driven by the crankshaft - these two elements in any internal combustion engine are interconnected by a belt, gear or chain drive. The camshaft rotates through the gear train inside the cylinder block. This gear rotates the camshaft in the cylinder head. Today, internal combustion engines are more common, where belts are used in the timing mechanism.

The latter have a simple design, such a mechanism is cheaper to manufacture. However, their reliability is much lower than in the case of a chain drive. The latter is more complicated - there are additional elements here. These are chain guides and idlers.

Why bend?

The situation when the valves are bent can happen in any engine of any design. It does not matter how many cylinders in the engine and how many valves it has. The reason for the breakdown is simple, and it is one. This is a broken belt in the drive or chain. The latter are torn much less frequently compared to belts. In the case of the chain, it stretches and the stars jump.

The camshaft stops abruptly after a broken timing belt. The crankshaft will continue to move. So, valves that are recessed into the cylinders will collide with the pistons when they reach top dead center. And since the pistons have a largeimpact energy will easily bend or break open flaps.

valve bend

Elimination of the consequences of this breakdown is very expensive. It is necessary to pull out all the damaged valves from the engine. The entire timing mechanism and the cylinder head also necessarily suffer. It is far from always possible to restore the cylinder head, and then only replacement with a new or contract one will help.

Causes of broken timing belt

The most common causes of drive belt breaks are owners not following the manufacturer's replacement instructions. When the car is new and under warranty, the owners very rarely look under the hood - all maintenance work will be performed by an authorized dealer. When the warranty ends, many try to save money on belt replacement.

It is not uncommon for a pump to fail. In many car models, it is driven by the timing belt. If the pump fails, the system will jam, and the belt will wear out in a few hours. Also one of the most popular reasons is poor quality belts. Therefore, it is better to purchase high-quality and original consumables.

Camshafts, as well as tension rollers of the timing mechanism, may also fail. The latter fall off or may jam - the belt either flies off the gears or a break occurs. That's why the valves were bent at the VAZ.

how to check if a valve is bent

It's not just a break that can happen to a belt. Often the teeth are cut off, and it is not so easy to find them. Teeth can slip if the spring breakstension roller. On some engines, the camshaft gear has a special conical fit. Only a tightened bolt serves as insurance against turning the gear. If it is not held out, then there is a risk that the gear will turn, and as a result, the valves will bend. Replacement is the only way out.

How to avoid trouble?

There is only one way. It is necessary to strictly follow the manufacturer's instructions for replacing consumables. Not only the timing belt is subject to replacement, but also the tension rollers, as well as other elements that are engaged with the belt and are indicated by the manufacturer in the regulations.

valve replacement

All accessories should only be purchased from trusted automotive dealers.

Can the starter be bent?

The starter bends the valves, and easily. This happens if it is incorrect to install the stars or gears of the gas distribution mechanism according to the corresponding marks. Then it is enough to turn the starter. If the engine starts, the driver will immediately learn how to recognize that the valves are bent. But if you miss the marks slightly, then damage can be avoided. In order to solve the problem completely, it remains to assemble the drive according to the rules.

How to spot bent valves?

It is impossible to determine by eye what bent the valves. To do this, you need to carry out simple, uncomplicated actions. First you need to install the timing belt according to the marks, and then turn the crankshaft manually. It usually takes two to five turns to find out that the valvesreally bent. If the crankshaft rotates easily and calmly, then the timing elements are intact. When rotation is difficult, the valves are damaged.

vaz bent valve

It also happens that with free and easy rotation of the crankshaft, the valves are still bent. In this case, you can identify the problem by measuring the compression. If the compression is at zero, then the timing elements are damaged. Many do not know how to check if the valves are bent. It will be heard. The engine will run unevenly. It feels good even on big engines with six or more cylinders.

Which engines don't bend valves?

Such motors exist. Some engines were even produced by AvtoVAZ. The whole secret is in pistons with special recesses on the working part of the piston. These recesses are made specifically for the valve. If the timing belt breaks, the element will simply go into these holes, and the structure will remain intact. It will only be necessary to set the gears on the marks and install a new belt.

How do you know if an engine is bending valves?

But this will not work. There are no tricks or signs here. It will not be possible to visually determine whether the motor is safe.

how to check if a valve is bent

Also missing inscriptions or any references. For information, see the instruction manual or contact your authorized dealer.


In order not to replace valves, it is recommended to change the timing belt in time. If this is an AvtoVAZ car, then you can installspecial protected pistons. But they eat up some of the power and increase fuel consumption. It must be remembered that when the timing belt breaks, not only the valves fail - the entire head may break. This makes repairs even more expensive. Don't skimp on the timing belt.

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