Do valves bend when the timing belt breaks?

if the timing belt breaks, this will mean quite a lot of damage to your engine and its parts, especially if you have an interference engine.

This can also mean trouble for the valves. To summarize how the valve mechanism works, at the moment the piston reaches the top dead center (TDC), both valves in the combustion chamber are closed, and a certain pressure is created in it. 

The top dead center or TDC means that the piston position speed is zero, and its position is the furthest from the cylinder head. Check the below image.

camshaft-on-a-4-cilinder-engine
source: Wikimedia Commons

A broken timing belt means that the valves do not have the necessary time to close before the piston arrives Because of this, a collision will occur between the pistons and the valves which directly leads to bent valves. Previously, in order to prevent such a problem, special valve grooves were made on older engines. 

On newer engines, similar grooves are also found, but they are intended only to avoid deformation of the valves during engine operation, and they do not protect the valves from bending when the timing belt breaks.

From a physical point of view, the moment the timing belt breaks, the camshafts stop immediately, under the action of return springs that slow down its cams.

The crankshaft, at this moment, inertially continues to rotate (regardless of whether the transmission was switched on or not, the speed was low or high, the flywheel continues to turn it).

So, the pistons continue to work, and as a result, they will hit the currently open valves.

What causes the timing belt to brake?

  • A most common cause is a bad or failing water pump.
  • A worn belt caused by the passage of time or prolonged use
  • Possible damages to the crankshaft.
  • The belt loosens or tightens because the tension rollers are unscrewed.

Considering the valves, modern engines, although more powerful than older engines, are much sensitive regarding this problem because of the small distance between the valves and the pistons.

So, if the valve is slightly open when the piston arrives, it instantly bends. Since for greater compression and compression in the bottom of the piston, there is no groove under the valve of the required depth.

On which engines do valves bend when the timing belt breaks?

First of all, in the symptoms of an incorrectly installed timing belt or chain article, I’ve talked about interference and non-interference engines. If you have an older car, then there are more chances for you to have a non-interference engine and you are lucky.

Non-interference engines do not suffer damage or bent valves if the timing belt breaks. The engine simply stalls and, when you replace the timing belt kit, you’re good to go.

However, on interference engines, meaning newer engine models, valves do bend when the timing belt breaks.

How to know if the engine has bent valves?

To know if you have bent valves you have to perform a proper check at a car workshop. Visual inspection in this case does not work. Even if you have information from the manufacturer about damage in the event of a belt break, it is not known how reliable it is.

Because most of the engines nowadays are interference engines, when the timing belt breaks, then simply changing the timing belt and ignoring the other consequences is not worth it. Trying this solution will only worsen the situation.

Even if the damage is small and the car will start, the engine will shake, and the consequences will only worsen. There is a way to check if the valves are bent without dismantling the engine.

How to check if the car has bent valves?

In order to check if you have bent valves, you will have to remove the timing belt and check the piston one by one when it is in the TDC position rotate the camshaft 720 degrees. If you did not encounter any resistance, you can continue checking the second piston, third, and so on.

To do that, you just have to use a wrench, put it to the crankshaft pulley, and rotate it 4-5 times, just like when testing if a timing belt or chain is correctly installed. If the movement is free and the resistance is not noticeable, then the valves are ok.

Although there are other ways to perform if the valves are bent or not, it is advisable to go to a car workshop and let authorized personnel do the tests. Bent valves are a serious issue.

Another check you can do is to see if the cylinder is sealed or not. To do that:

  • choose a piece of hose according to the diameter of a spark plug shaft;
  • unscrew the spark plug;
  • place the cylinder piston in the top dead center (TDC – valves closed) one by one;
  • insert the hose tightly into the well;
  • try to blow hard in the combustion chamber. If air passes, then it is bent, if it does not pass, then it is not bent.

You can also check using a compressor. It will take a little bit longer. Find the central electrode in the old spark plug and put a hose on the ceramic tip (fixing it well with a clip), then pump pressure into the cylinder.

Conclusion

If the timing belt breaks, this could cause a lot of problems to your engine and will lead to costly repairs. In order to prevent that, you constantly have to monitor the condition and tension of the belt. When the slightest unfamiliar noise appears during operation, you should immediately try to find out the cause, and inspect the condition of the rollers and the pump.

When buying a used car, replace the timing belt as soon as possible, regardless of what the seller told you. This is a must for a recently purchased car.

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