Can A Car Run With Bent Valves?

Can A Car Run With Bent Valves?

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Can A Car Run With Bent Valves?

It will depend on how many bent valves we are talking of. Additionally, it will still depend on how bent they are.

Too many cylinders lacking compression will mean that it won’t start. If the valves foul piston motion due to the way they are bent, you will not start the car.

Yes, Valves can contact the top of a piston due to incorrect engine synchronization dictated by timing chain/belt damage and incorrectly fitted new belts and chains. While an engine with bent valves might start, it will run poorly.

But if you have some of the valves at least somewhat intact, the car will start. My V8 burnt two valves, and I used it for over a week until I got it fixed.

It was running very poorly on 6 cylinders, but I didn’t have a choice.

However, some modern cars might show every light on the dash, going to rescue mode, and possibly the computer might prevent the car from starting the engine and even shut it down.

We need to understand that burnt valves are not the same.

Consequently, it’s unlikely that all valves will be burnt or bent, and the damage will still not be sufficient not to allow some level of compression.

Still, you might be courting more damage if you try running a car with bent valves, depending on the model and age of your car.

The most common undoing of valves is breaking or bending when they contact the pistons.

Will An Engine Start With Bent Valves?

When you have an engine with bent valves, it mostly results in imbalanced compression.

And if the pressure is too low, the combustion process gets affected, and you will have an incorrect burning of fuel.

Anytime you have a bent engine valve, you will have low compression since it no longer closes securely, meaning it will make the seal defective with the cylinder head.

It’s important to avoid conditions that can bend valves like engine overheating and lack of lubrication.  

This is primarily the case for overhead valve engines where overheating causes lifters to stick, leading to not only bent valves but also bent pushrods.

But if you find yourself with bent valves, the best thing you can do is to have them replaced immediately or as soon as it’s practically possible.

Generally, this will require removing the head from the vehicle and replacing the valve. You will also need to reface and assemble with a new head gasket.

But be prepared to address potential further damage, especially if the can has run for some time with bent valves.

Engine design will also dictate how much repair and parts need to be replaced.

Can Bent Valves Cause No Start?

Bent engine valves are notorious for causing an imbalance of compression.

When the compression is too low, there will be a negative effect on the combustion process, and the fuel will not burn correctly.

Consequently, the bent engine valve will create low compression as it can’t close securely. This leaves the seal defective with the cylinder head.

Valves can bend due to several reasons, including lack of lubrication. Also, engine overheating will cause bent valves, especially for overhead engines.

This type of engine will cause lifters to stick, resulting in not only bent valves but bent pushrods as well.

When you encounter a bent valve, your best option will be to have it fixed without any delay. And this will require taking off the head and carrying out your valve replacement.

You will also need to reface and carry out the assembly with a new head gasket and possibly more parts, but it will depend on the engine design.

Remember, you might experience more damage that the bent valve might cause to other engine components.

Therefore, you will want to take note of the signs of a bent valve before it causes damage and wreaks havoc on your engine.

For instance, burnt or bent valves will cause your engine to misfire. Consequently, your car’s engine might jerk, hesitate, or stall when the car is in motion.

And as a result, you will find that your car’s fuel consumption might increase if it is misfiring, thanks to the bad valve.

Can You Bend Valves By Turning The Engine By Hand?

It depends. You might not be able to bend valves by turning the engine with your hands. However, if the engine has incorrect timing, this is possible.

As long as the timing belt or chain has snapped, you can bend valves if you turn the engine by hand.

But for this to happen, the engine will have to rotate some speed to make pistons hit your engine valves hard enough to bend them. Not a very likely scenario, but it can happen.

You might be staring at potential backfiring with bend valves as they won’t form a proper seal.

Consequently, air and fuel will flow back into the exhaust or intake, where combustion occurs.

Fortunately, modern cars will not generally backfire due to this reason, but it’s very real in older cars. Issues with the valve will always affect the car in one way or the other.

For instance, you might lose compression if you have bent valves, a broken piston ring, or a hole in the piston’s top. And this might equate to a no-start condition, although not always.

Replacing or fixing a broken valve is not cheap. You will be expected to spend between $900 and $2000.

The situation only gets worse with careless continual to drive your car when it is clear that you have a bent valve.  You will pay for such behaviors once you get to the repair shop.

Do Valves Bend When The Timing Belt Breaks?

It depends. But one thing is certain: when the timing belt breaks, it will lead to a lot of damage to the engine and many of its parts.

The situation is especially extreme if what you have is an interference engine.

A broken timing belt will naturally spell trouble for the valves. But you will understand it better if I explain how the valve mechanism works.

When the pistons reach the TDC (Top Dead Center), the two valves in the particular combustion chamber will be closed, creating a certain pressure.

The top dead center means that your piston position speed is zero, the furthest from the cylinder head.

As long as a timing belt gets broken, the valves will not have the needed time to close before the arrival of the piston.

Consequently, there will be a collision between the valves and the pistons, directly leading to bent valves.

Older engines had a way of preventing this since they had special valve grooves, but this is only a thing in the distant past.

Previously, special valve grooves(Amazon Link) were made on older engines to prevent such a problem. While similar grooves can be found on newer engines.

They are designed only to avoid deformation of the valves when the engine is in operation, scarcely protecting the valves from bending should the timing belt break.

Technically, the camshaft stops as soon as the timing belt breaks due to return springs that slow down its cams.

However, the crankshaft will at this moment continue to rotate due to the force of inertia, notwithstanding the transmission was switched on or not.

Whether the speed was high or low, or if the flywheel continues to turn it. And as the pistons continue working, they will hit currently open valves.

Will A Bent Valve Hold Compression?

No, not enough. A bent valve will not hold enough compression since the fuel/air mixture will push back out the exhaust or intake.

If you want to feel the compression, you will only need to turn the engine over using a ratchet and socket on the crank pulley.

When you do this, you will feel each compression pulse. So it will be possible to realize or notice when each cylinder is compressing.

As you might know, four crank rotations make 1 complete cycle. However, to be accurate with the measurement.

You can get a compression tester and then screw it in your spark plug holes, unhooking the coil, and crank the engine.

It will be pretty easy to find any cylinder with a problem with this method.

The best test is a leak-down test, as it lets you know the extent of the leak (if it is a major or a minor leak). A major leak will mean that a bent valve is not sealing.

And if you listen to the intake manifold or even the exhaust, a bent valve will make you hear the sound of air passing.

There should be no leaks as long as there is no bent valve, just the little that gets by the worn rings.

While a bend engine valve will cause misfiring and make the check engine light come on, there are other effects it will have on your car, like impacting your car’s performance.

The distinction of the check engine light will be that it will keep on flashing.

Should You Be Able To Turn The Crankshaft Pulley By Hand?

No, It’s not possible to turn the crankshaft pulley by hand. Indeed, you can turn some pulleys like the alternator pulley, the water pump pulley, and the power steering pump pulley.

It’s normal and understandable that you cannot rotate either the crankshaft or cam pulleys by hand. But if you can rotate them by hand, you have a problem.

Therefore, if you want to rotate the engine by hand, you will have to place a large socket on your front crankshaft bolt and then attach a long ratchet wrench to rotate the crank.

The movements’ precision will improve with a longer wrench.

Crankshaft or engine rotation is the direction your car’s engine spins. It is either counterclockwise or clockwise. The standard rotation is counterclockwise.

But you will find a few cars with a clockwise rotation.

If you wish to disassemble the crankshaft pulley, you will first need to place one end on the bolt-removing tool to slacken the bolt or even use an impact wrench.

Tighten the bolt remover tool until the crankshaft pulley is completely released.

When working on the crankshaft, you will want to avoid turning it the wrong way since if you turn it backward.

The timing belt might jump a tooth since the tight side of the belt is relaxed while the slack side is tightened.

Although the slipping of the belt might not do any serious damage, it is advisable to reinstall it as per the garage instructions.

Will Compression Test Show Bad Valves?

Yes. Generally, the user will only notice a bad compressor valve over time as the compressor becomes increasingly inefficient.

And because this does not happen overnight, but year over year, the full extent of the damage may not be realized.

But the maintenance technicians are the ones who discover such problems as they conduct regular inspections of the system.

Professionals use gauges to test the pressurization and compression of the system, tracking its performance as it cycles on and off.

Compression tests will show if a compressor has bad valves and make you aware that the system has a build-up that will get it flooded every time it turns on.

It’s needful to note that the compressor has a high-pressure side and a low-pressure side. The difference in pressures is what allows contraction and expansion.

But when valves start to go bad, the engine cannot perform as it should as the pressure differences start to equalize across the entire system.

Bad valves will cost you money in the long run as they lead to poor fuel efficiency if you are lucky enough to ride the car in that condition.

Additionally, when valves go bad, overheating is a widespread occurrence. Therefore, this is a matter to be concerned about.


A car can run with bent valves, but you might not want to do that as it will cause more costly damages over time.

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