The consequences of a broken timing belt depend on the design features of the engine and on the operating mode at the moment the valves meet the pistons. Let's look at the causes and consequences of a broken timing belt and tell you how to determine whether the valves are bent after a chain or timing belt has jumped.
On what engines does the valve not bend?
When the timing belt breaks, the reciprocating motion of the pistons is maintained, since the inertial force of the flywheel continues to rotate the crankshaft. But since there is no synchronization between the camshaft and the crankshaft, certain valves remain open as the pistons approach top dead center (TDC). This is how the valve plates “meet” with the pistons.
Why is it that on some engines, when the timing drive overshoots or breaks, the valve does not bend? The answer is in the special design of the pistons, which have special recesses. Due to the “counters”, there is a gap between the pistons at TDC and the fully open valves, which protects the parts from damage if the belt breaks. Look for information about the design features of your car’s engine model in the technical documentation.
For example, VAZ engines models 11186 and 11189, produced before 08/15/18, were “plug-in”, but after this date they were equipped with a modified piston group, eliminating the risk of pistons hitting the valves if the timing belt breaks.
There are rarely engines on which belt destruction during idle does not lead to bent valves (for example, 4A-GE from Toyota). Some manufacturers reduce the risk by making the pushrod material brittle. This solution is found on the 1.7 DR diesel engine from Opel, on which, when “meeting” at low speeds, the consequences are limited to only a few burst pushers. Such solutions are rare in global engine building practice, so on almost all diesel engines, a broken timing belt leads to bent valves.
What happens to the engine when the belt breaks?
What happens if you drive with a handbrake and what consequences will arise?
While the car is running, the engine pistons move in a certain direction. The piston moves down during the intake stroke and rises during the exhaust stroke. When the cylinder block is at the top point, each valve must be closed.
When the timing belt is torn, the valve stops rotating and stops. However, the crankshaft rotates and the pistons are directed towards the open valves. After their meeting, the parts bend and become unusable. Regardless of whether the car is idling or in gear, the likelihood that the pistons will knock on the valves and bend them is quite high.
But still, the higher the speed, the worse the likely consequences. In addition to the fact that the valves will be damaged, the pistons may be damaged and the guide bushings may burst.
Causes of timing belt breakage
- Failure to comply with the service interval for replacing the timing belt.
- Too much or insufficient tension force.
- Contact with engine oil and other technical fluids on the working surface of the belt that reduces the engagement between the belt teeth and gears. Often in such cases, the belt first jumps 1-2 teeth, after which the engine loses power, starts poorly and may run unstably.
- Foreign objects getting under the belt. On most cars, the gas distribution mechanism drive is protected by a plastic casing. If the latter is damaged or incorrectly installed, dirt and small stones entering the working area will shorten the service life of the belt and rollers and can even cause a break.
- Water pump jammed. If the bypass or tension roller jams, the breakage does not occur instantly. Due to increased friction, the outer zone of the belt begins to heat up quickly. If you notice the smell of burnt rubber in time, listen to the extraneous sound from the timing drive and turn off the engine, you will be able to protect yourself from the costly consequences of a broken belt.
- Incorrect redistribution of force on the belt teeth. The reason should be sought in the misalignment of pulleys, gears, idler and tension rollers. Pay attention to the wear of the teeth of the crankshaft gear, camshaft, and fuel injection pump. At high mileage, due to wear on the gears, the belt teeth grind down, which reduces its service life and increases the risk of skipping/breaking.
- Failure to follow the recommendations for assembling the timing drive and handling the new belt.
- Defects in production or selection by the manufacturer of low-quality raw materials for the manufacture of a belt.
Reasons for the breakup
The main flaw of the belt on the Priora (we chose it as an example, but there is no fundamental difference with cars that use a similar type of distribution mechanism) is that it is made of rubber. Accordingly, if the belt is not replaced by the end of its life, the rupture will occur spontaneously and it is impossible to predict this moment.
For modern cars, the only problem with a broken belt is the fact that it breaks. On older cars, a torn belt also means that your valves are bent. In new cars, special grooves are made in the pistons for the valves, due to which such an annoying nuisance does not happen. The 16-valve engines on the Priora are exactly like this. On old VAZ 2109 and 99, if your valves are bent, then you will have to spend a lot of money on repairs.
The belt will break due to the following reasons:
- End of service life.
- Oil leaking from under the block head.
- Broken rollers or tensioner.
Wearing the belt before the deadline is the most common mistake of people who operate a 16-valve engine in a Priora. Therefore, in this case, you need to focus on the recommended mileage indicated by the manufacturer, closer to which it is recommended to replace the belt. At the same time, if you do not want the valves to bend, then replace the belt a little before the expected date.
Another problem for engines that have been running for more than a hundred thousand kilometers is oil leakage. According to the regulations, it is recommended to rebuild a 16-valve engine after the first 150 thousand mileage and replace all rubber elements. If the gasket was not replaced on time and oil from under the valve cover or cylinder head flows onto the drive surface, then you are guaranteed to bend the valves soon (if on your engine, in the event of a break, the valves bend. You can find out more information in the documentation for maintenance of your vehicle). When oil gets on the belt, it causes fatigue aging; the rubber becomes unusable and thins out under the influence of an aggressive environment. The consequences will not be long in coming, so oil leaks should also be considered as signs of a rupture.
Another factor that influences the condition of the timing belt is the auxiliary components that ensure the movement of the belt. On a Priora with a 16-valve engine, idler rollers and tensioners are involved in the movement of the belt.
Jammed roller
The condition and normal operation of these mechanisms should also be considered as signs of rupture, since if some auxiliary mechanism jams while driving, the belt will burst
To prevent this from happening and to prevent the valves from bending, you only need to pay attention to the condition of the auxiliary components of the gas distribution mechanism when performing maintenance. If you notice that something is wrong, then refrain from traveling until the corresponding unit is replaced
Signs of a broken timing belt
When the timing belt breaks, the engine stalls abruptly, and a loud bang is heard from the engine compartment (you can’t always hear it if the car is moving at high speed and low revs). The engine will not start after this. When cranked by the starter, the crankshaft rotates faster than usual. If the timing belt on a car breaks, the characteristic sound of the crankshaft rotating “idling” indicates a lack of compression in the cylinders.
Replacement
If the timing belt breaks (whether it’s a VAZ or a foreign car, it doesn’t matter), the first step is to install a new element. There are two reasons for the impending replacement:
- Natural wear and tear. Manufacturers recommend replacing the element at least once every 80 thousand kilometers. However, it is not uncommon for a belt to “nurse” for 150-200 thousand without deformation or whistling. But this does not mean that the replacement can be postponed indefinitely. This can lead to expensive repairs.
- Mechanical damage. The belt structure may be damaged due to gross errors during installation. This is a mismatch of marks, insufficient or excessive tension of the element. Also, the belt breaks (more often than not it simply falls off) during active driving “before the cut-off”, which is accompanied by sharp braking. If the car is “chipped” with a cutoff offset, there is a high probability of a belt break. Therefore, you should not often operate the car under heavy loads.
Consequences
On many engines, the consequences of a broken timing belt extend beyond bent valves. If trouble occurs while driving at high speed and high revs, the force of the impact may be sufficient to damage the pistons and disrupt the geometry of the valve liners. The consequences can be fully assessed only after the cylinder head is removed.
If the belt breaks at idle and it is not known for sure whether the valves on the engine are bent, you should install a new belt and measure the compression in the engine. The performance of each cylinder should not differ by more than 1.5-2 atm. To avoid further harm to the motor, use an endoscope with a rotating camera. It will not be possible to assess the degree of deformation of the valve stem, but you will be able to see marks on the pistons from the impact.
If, after installing a new belt, the engine starts, but runs unstable (troit), the valves are still bent and you should prepare for serious repairs.
In addition to a new timing kit (belt, rollers), it will be necessary to replace the intake/exhaust manifold gaskets and other seals that will not be suitable for reinstallation. During the repair, you should check the water pump, the condition of the valve seals and the piston group.
Video: Broken timing belt. What is the threat?
Procedure for replacing the timing belt
To remove the old timing belt, you must perform the following steps:
- Remove the timing case, which is secured with several bolts.
- Unscrew the fasteners on the crankcase protection.
- Remove the belt from the compressor by dismantling it, remove the belt and return the compressor to its proper place.
- Remove the belt from the generator.
- To de-energize the contacts, you must remove the terminal from the battery.
- Unscrew the fasteners on the engine and remove the generator, terminal and water pump pulley, remembering to first remove the corresponding bolts.
- It is possible that it will be necessary to dismantle the base of the power unit.
- Remove the protection cover from the timing belt.
After completing all these steps, you can make a replacement. To do this, you need to remove the cover from the toothed pulley and remove the torn timing belt. Then you need to install a new blade, not forgetting to tighten the tensioner. If wear is detected on the rollers, they also need to be changed. Then perform the steps described above in reverse order to return the structure to its original state.
Please note! For a specific car model, there are characteristic nuances in removing and installing the timing belt, although in general they are very similar.
Belt Drive Condition Assessment
The average service life of a timing belt is 50-70 thousand km. The exact replacement intervals are indicated in the repair and operating manual for your car. In situations where, after purchasing a car, there is no reliable information about the timing of previous maintenance of the timing drive, the need for urgent replacement can be understood by the following signs:
- Cracks in the belt base.
- Wear of the upper edge of the teeth.
- Oil on the timing belt.
- Noise from the pump, tension or idler pulley.
- Worn belt edges.
Symptoms of a break
The timing belt is good for everyone, but unlike the whistling alternator belt, it breaks without any signs of it. It’s clear how the engine’s performance changes when the belt breaks - it stalls, which is why the battery icon and oil can light up even on the meager panel, and the accelerator pedal does not respond. This ends the list of safe symptoms of the problem. Yes, they may advise you to crank the engine with the starter and it will definitely not start. But later you will understand that this is fraught and, moreover, in the absence of experience, does not definitely indicate that the belt drive has failed.
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Due to the actual absence of symptoms of a break, they do not like the belt, knowingly treating it with caution. After all, in fact, you can make sure that it is torn only by opening the plastic timing case or opening the inspection window, if one is provided for by the protection design. If you think about it for a moment, this must be done after every sudden stop of the engine, even if it was caused by an electronics failure. As they say, it's better to be safe...
It is rare that a break is preceded by any squealing or other noise. In this vein, everything usually goes silently.
How to avoid timing belt breakage?
- Follow the replacement periods prescribed by the manufacturer.
- Once every 15-20 thousand km. inspect the gas distribution mechanism drive for oil fogging and antifreeze.
- On runs over 150 thousand km. Whenever you replace the timing belt, inspect the sprockets of the camshafts, crankshaft and injection pump for critical tooth wear.
- Install a high-quality timing kit from a trusted manufacturer.
Many reputable companies allow you to verify the authenticity of their kits. To do this, the packaging has holographic protection and/or a code that must be entered into the decoder on the manufacturer’s website. There is a hologram, after scanning which the buyer receives a notification about the authenticity of the purchased product.
Checking the performance of the belt
Following the factory documentation, we can say that checking the 16-valve engine on a Priora is required every 20 thousand mileage of the car (take into account the quality of spare parts and the large number of fakes). This should be done in the same way as on the old nines:
- The front end is raised on jacks above the ground to a distance sufficient to get under the car.
- Engage 5th gear.
- Open the protective cover or remove it so that the inspection does not damage it.
- Now you need one person to rotate the wheel while you inspect the drive for damage.
If during inspection signs of an imminent break were noticed, then it is advisable to make a replacement. The following defects should be considered as signs:
- Torn teeth.
- Cracks.
- Oil streaks on the surface.
If you haven't noticed anything like this, then you can safely drive. If you neglect it, the consequences in the form of bent valves will cost you a pretty penny.
What to pay attention to during the renovation process?
The success of the repair largely depends on the correct troubleshooting of the gas distribution mechanism parts and the cylinder-piston group. If the timing belt breaks, pay special attention to measuring the protrusion of the pistons and checking the geometry of the valves. Check the condition of the valve guides and the chamfers of the valve seats in the cylinder head. Requirements for serviceable valves:
- the diameter of the valve stem is the same along the entire length of the stem;
- plate runout no more than 0.025 mm;
- the beating of the rod over a length of 10 cm does not exceed 0.015 mm;
- The valve chamfer has no deep damage.
To check the runout of the rod and disc, the valve is mounted on a pair of V-shaped stops. The measurement is carried out with a dial indicator mounted on a special stand.
What does this lead to?
If your timing belt breaks, the consequences can vary. As we said earlier, it all depends on the design of the power unit. Here you can be guided by the principle “the simpler the motor, the more reliable it is.” When the engine is in the TDC position, the valve does not reach the bottom of the piston, nothing will happen. In this case, if the timing belt breaks, only the purchase of a new product can be included in the expense item. All valves will remain intact without damage to the stem geometry.
Rules for handling a new timing drive kit
- Do not roll the belt into rings or allow the timing belt to bend or twist, as this may damage the elastic cord.
- Some car manufacturers have developed an installation tool for servicing the timing drive. The use of any other tool can lead to a shift in the timing of the gas distribution mechanism and damage to the belt. An error with setting the marks is fraught with unstable engine operation, loss of power, and even “meeting” of the valves with the pistons.
- Never reinstall a used belt.
Modern timing belts use fiberglass cord. It has a large margin of tensile strength, which entails a loss in elasticity. Therefore, the belt must not be bent or broken. This can damage the elastic cord and shorten the service life of the belt.
Selection of instruments and start of the operation
So, if your timing belt has already broken, or you decide to change it yourself, then you need to start with preparation. If it has come to this, then you need to know that the belt on 16-valve engines on the Priora is changed along with the idler rollers and tensioners - their service life is designed so that they fail approximately at the same time. If you change one drive, it is possible that the belt will burst while driving and this will lead to breakdown of all drive components. Some car enthusiasts noted that at the end of their service life, the idler pulley was bent and because of this, even the new belt was torn.
Cost of work
If the timing belt breaks (including 2112) without bending the valves, the cost of replacing it will be about 500 rubles. But if you have certain skills, you can do it yourself. Thus, the breakdown budget will be no more than a thousand rubles.
At the same time, it is recommended to check the condition of the pump impeller and tension roller - they should rotate smoothly, without sounds or play. If a wedge occurs and valves need to be replaced and the cylinder block repaired, the cost of the work can reach 40-50 thousand rubles. If it is an old foreign car, it is easier to install a contract engine from disassembly - in some cases it is actually cheaper than repairing the old one. Well, in order to prevent such a situation, monitor the tension of the element and its external condition, and most importantly, observe the replacement frequency of 60-80 thousand kilometers. Even if after this period the belt does not pose a danger (without deformations or extraneous sounds), it would not be superfluous to play it safe by installing a new element in its place.
Sources
- https://autostrong-m.by/post/obriv-remnya-grm-prichini-i-posledstviya
- https://tolkavto.ru/remont-i-obsluzhivanie/dvigatel/posledstviya-obryva-remnya-grm.html
- https://rad-star.ru/pressroom/articles/obryv-novogo-remnya-GRM/
- https://autobann.su/porvalo-remen-grm.html
- https://kodobd.top/remen-grm-porvalsya/
- https://grmexpert.ru/o-grm/lopnul-remen-grm-chto-delat-prichiny-priznaki/
- https://rad-star.ru/pressroom/articles/chto-delat-esli-porvalsya-remen-grm/
- https://FB.ru/article/277704/porvalsya-remen-grm-posledstviya-i-chto-delat-dalshe
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