Variable Valve Timing [explained by Expert]

Before you can say a vehicle is in good working condition, all the various components have to be in place and working. Some of the components are infrequently required, such as windshield wipers, spare tires, and carjacks.

While others like the brakes, timing belts, engines, valve timing, to mention only a few, are compulsory for any car to even move. In any event, both classes of automobile components are essential and must function optimally at all times.

As a car owner or an enthusiast, chances are you've heard the sentence, "that engine is out of time.” Whether it's from your mechanic or an automobile show on television, it means one thing. And that's a timing component in your car's engine that is faulty. But what does it exactly mean?

Inlet and exhaust valves

Inlet and exhaust valves[/caption]Every four-stroke engine generally needs both timings to be correct: Valve timing and ignition timing. While it will touch little on ignition timing, this article is primarily about valve timing.

Seeing as valves are crucial to the effective functioning of every vehicle, we won't be doing this alone. We've recruited the expert help of a professional mechanic with more than 20 years of experience to guide us. He will be working us through the importance, functions, and other concerns about valve timing.

Valve timing

Valve timing

Valve timing is the mechanism that determines the precise time engine valves are to open and close. If an engine is to work correctly and efficiently, the engine valves must open and close at the exact required times. The two main valves in any car engine are the inlet and exhaust valves.

The intake valves allow the mixture of fuel and air (also known as the charge) into the engine. The exhaust valves let them out. If something happens to prevent the timely completion of this automated process, the car engine will not run. What's more, if the valves open at the wrong time, the piston may hit them and cause them to bend.

Valve timing is as crucial as it's complex, and it's typically set at the factory. Unless for when you need to reset and modify it. The precise time your car's intake and exhaust valves open and close will determine the power your engine generates. As well as at what revolution per minute (RPM) it will be produced. The camshaft controls the valve timing.

Why is valve timing important?

Valve timing controls the flow of the air-fuel mixture into and out of the combustion chamber of the engine. The combustion chamber is the part of the engine where the pistons compress the mixture of fuel and air to aid combustion.

This is the simplified explanation of how power is produced for your car to run. In summary, accurate valve timing ensures that your car can run in the first place. And when it does, that it's at optimal capacity.

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How does it work?

Valve timing is the most critical process of internal combustion (IC) engines. Think of the engine valves as the human nose. Your vehicle engine uses valves for its ‘breathing’ process—inlet (inhale) and exhaust (exhale).

The camshaft controls the opening and the closing of the valves at specific intervals. The timing intervals are designated in degrees to correspond to the positions of the engine's pistons.

Inlet valve

 Inlet valve

The air-fuel mixture possesses both motion and mass. And due to the smallness of the inlet valve's opening, the entire air-fuel mixture can't enter the cylinder. Not even when the piston gets to the end of its downward stroke. This causes the pressure in the combustion chamber to maintain a level below the atmospheric pressure.

While the charge moves with high velocity towards the moving piston. At this point, the inlet valve stays open until the piston goes into its next upward stroke, which is also known as the compression stroke.

Exhaust valve

car exhaust valve

When the piston enters the exhaust stroke, it again moves upwards. Thereby ejecting the exhaust gas out via the now open exhaust valve. The exhaust valve opens before the piston gets to the before-dead-center (BDC) in its series of power strokes.

Like this, some of the pressurized exhaust gases escape even before the piston begins its upward stroke. The exhaust valve then closes after some moment (degrees) of reaching the top-dead-center (TDC).

At what position is valve timing set?

Whenever your car engine is reassembled, the valve timing has to be set. As simple as it seems, it could be the thing that makes or breaks your engine.Set the engine at the Top-Dead-Center (TDC) of the compression stroke and set the timing marks on the camshaft. That should get you going.

Can you replace valve timing yourself?

No, you can't and you shouldn't even try. Let a professional mechanic handle it.Valve timing is to be set according to the manufacturer’s specs. To do this, you need a specialized automobile skill set. The chances of fouling up valve timing are fairly high when you do it yourself.

What happens if valve timing is incorrect?

If the valve timing is set incorrectly, the engine will not run, but that's not all. The piston may also ram into the valves causing substantial damage. At the very least, it leaves bent valves and damaged pistons. Also, excessive fuel will be found at the plug surface. And the acceleration of the vehicle will become inefficient. This will usually show itself in the sound.

What is late valve timing?

Late valve time can occur in two ways. First, it can be when the inlet valve opens too late. This leaves the engine with poor cylinder filling for the intake strokes, consequently reducing suction. The second is when timing closes the exhaust valve later than normal. This reduces vacuum and compression. The camshaft position sensor will indicate if it's set right or wrong.

What causes late valve timing?

It happens when it's calibrated wrongly. It could also be that the valves are damaged and need replacement.

How do you read valve timing?

This is better left to a professional mechanic.

How does Valve Timing affect engine performance?

A great deal of the engine's efficiency and overall health depends on the valve timing and how well it functions. Bad valve timing can drastically reduce the performance of your engine. For instance, If the timing is incorrectly set, it can damage the engine.

If you're lucky, you will only need to rebuild it to bring it back on track. If you're not so fortunate, you will be left with the more expensive option of getting a new engine.Valve timing can also influence the following:

  • Spark plug function
  • Car acceleration efficiency
  • Power

Is valve timing the same as ignition timing?

No, they are not the same even though their functions are interconnected. For one, both of them are important in the way they contribute to engine performance, but they do so in vastly different ways.

On one hand, valve timing refers to the precise times the inlet valves take in the air-fuel mixture and when the exhaust valve lets it out. Ignition timing, on the other hand, describes when the spark occurs in relation to the workings of the crankshaft and piston.

Does either timing affect vacuum?

The simple answer is that it does. The much longer answer which shows why is given as below.Vacuum is a good way to determine engine efficiency. It indicates the capacity of the engine to draw in air into the cylinder on the intake stroke. But if the timing is incorrect, it means the valve will open either too early or too late.

This will consequently cause the combustion process to occur either too soon or not soon enough. In any case, pressure not fully evacuated during the exhaust stroke will be left in the cylinder. This residual pressure will imply that less air will be drawn in on the next intake stroke. Vacuum is therefore impacted.

Variable valve timing

As has been mentioned already in this article, a car engine ‘breathes’ through its valves much like how humans do with their noses. And in humans, the rate at which we breathe is primarily determined by the amount of work the body is doing. For instance, a person who is sitting and relaxed will breathe slower than another person who is running.

This is because our bodies will need more air intake as more work is required of it. It's similar in vehicles. When the car is running at a high speed, the engine will need to open its inlet valves faster, sooner, and often for a longer period. This is because the engine needs to produce more power faster to maintain the speed.

And for that, it needs to take in more air-fuel mixture to burn and generate power. In older engines, the interval for valve opening was optimized for just for single-engine speed. So, as the engine speed increases, the time required to fully fill the cylinder reduces.

This will cause the engine to continually receive less amount of air-fuel mixture. As a result, the engine will suffer power loss. To close this loophole, automobile manufacturers developed Variable Valve Time (VVT) systems.

The sole function of the VVT is to vary the opening and closing of valves for newer engines that are optimized for multiple engine speeds. At high speed, the inlet valves open earlier, and vice versa. This invention improves the engine's breathing as well as its ‘volumetric efficiency.’

Variable valve timing (VVT) solenoid

Variable valve timing (VVT) solenoid

Variable Valve Timing (VVT) mechanisms are built to reduce emissions, improve engine performance, and fuel mileage. The electro-mechanical system relies on the optimal flow of engine oil. Improper or failed oil circulation can cause damage to VVT components.

The variable valve timing solenoid is the component of the VVT system that manages the oil flow in relation to the engine speed and load. A properly functioning VVT solenoid will improve engine performance and fuel efficiency.

Where is the VVT solenoid located?

It's typically situated on or around the cylinder head block.

Can you drive with a bad VVT solenoid?

Yes, you can. But only for a limited time usually, before the car engine breaks down.

Can a faulty VVT solenoid cause a misfire?

Yes, it can and it often does, causing the engine to have acceleration problems and inconsistent idle.Dirty oil or sludge can clog the solenoid monitor, causing it to fail, consequently making all the cylinders misfire.

What happens when the variable valve timing solenoid goes bad?

When the VVT solenoid is malfunctioning, the entire system can be compromised, which may result in intake and exhaust valves opening and closing at the wrong time. This typically causes the fuel economy to drastically reduce.

What are the symptoms of a bad variable valve timing solenoid?

When your VVT solenoid goes bad, your modern car will try to warn you. Below are some symptoms to look out for:

1. Illuminated check engine light

This is the blessing of modern cars, the engine control unit (ECU) will warn you as soon as there is a problem with any component of your engine. The Check Engine Light will come on if your VVT solenoid is faulty.

2. Dirty engine oil

This is both a cause and a symptom. Keep the oil clean to avoid damaging the solenoid. If you see dirty engine oil, however, the VVT solenoid may in fact already be bad.

3. Poor fuel economy

The whole point of the variable valve timing system is to ensure maximum engine performance while reducing fuel consumption. A bad VVT solenoid compromises this system, often resulting in the reverse.

4. Rough idle

Additional oil may be passed to the VVT gear If the VVT solenoid is bad,. The revolution-per-minute (RPM) of the engine will begin to fluctuate and this can cause the rough idling of the car engine.Pro tip: As soon as any of these symptoms are observed, take your car to an ACE certified mechanic workshop to get the solenoid fixed. Further delay can damage your engine.

Final word

The valve timing and whole variable valve timing system including the solenoid are important to the effective functioning of all modern vehicles. They must work well at all times. In the event where they don't, promptly take your car to a professional mechanic to check it out. Any delay may cost you your engine.

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