So, the main function of automotive engine valves is, to let air in and out of the cylinders.
As a result, the valves in your cylinder head, are a vital component of your engine and undergo enormous stresses.
So, automotive engine valves are designed to open and close, at precise moments.
The automotive engine valves that let the air into the cylinder, is the intake valve.
The automotive engine valves that let the gases escape, are the exhaust valves.
Overhead Valve (OHV) – Overhead Camshaft (OHC)
The overhead valve engine (OHV), operates by using pushrods.
An overhead camshaft engine (OHC), needs fewer parts to operate the valves. The camshaft operates directly on bucket tappets.
This is why, automotive engine valves, play a pretty critical role in an engines performance. So, the more air you can move in and out of the engine, the more efficient it will be.
Intake valves handle cool, low pressure, low density gases.
Exhaust valves handle hot, high pressure, high density gases.
Damaged Automotive Engine Valves Can Result In:
- Reduced power
- Poor fuel consumption
- Complete engine failure
Automotive Engine Valves – How They Can Fail
Any valve will eventually wear out, if driven enough miles. But, many valves call it quits, long before they should. Usually, because of burning or bending:
Exhaust valves are the ones most likely to burn. Because, they run hotter than the intakes. Consequently, caused by combustion gases, escaping between the valve and valve seat. As a result, the hot combustion gases are forced past the valve; which starts to burn away the edge of the valve.
So, a burnt valve will cause issues with your vehicle’s performance and fuel consumption. Consequently, rough idle, reduced power, backfiring and misfires are all symptoms of burnt valves. Incoming air and fuel, cool the intake valves. As a result, they operate at a much cooler temperature.
The most common failure of valves is bending or breaking. As a result, of contact with the pistons. The valves contacting the top of a piston, is due to incorrect engine synchronization; caused by timing chain/belt breakage. Finally, if you suspect your engine may have bent valves, it is crucial not to attempt to start the engine.
The bent valves above are, a result of a fatigued timing belt that has broken. Your timing belt doesn’t last forever and needs to be replaced; according to the manufacturer’s service guidelines. Replacing your timing belt is cheap insurance, against costly engine damage.
How Are Automotive Engine Valves Cooled
So, good valve seat contact is essential to prevent burning. If the valve does not receive adequate cooling, it can overheat burn and fail.
Leaking Automotive Engine Valves
The cylinder leakdown test is an excellent way to pinpoint, where problems are before tearing down the engine. Listening for where the air is escaping, by ear can isolate the problem.
Intake valve : Air whistling out of the intake, carburetor or throttle body, indicates a leak at the intake valve.
Exhaust valve : Air heard hissing out of the tailpipe, turbocharger or exhaust manifold, means an exhaust valve is leaking.
How Many Valves Can You Have
A multi-valve engine design typically has three, four or five valves per cylinder, to achieve improved performance.
Three-valve cylinder head
So, this has a single large exhaust valve and two smaller intake valves. A three-valve layout, allows better breathing than a two-valve head. Consequently, the large exhaust valve results in an (RPM) limit, no higher than a two-valve head.
Four-valve cylinder head
This is the most common type of multi-valve head; with two exhaust valves and two similar (or slightly larger) inlet valves. This design allows similar breathing as compared to a three-valve head. The small exhaust valves allow high (RPM). As a result, this design is very suitable, for high power outputs.
Five-valve cylinder head
Finally, less common is the five-valve head, with two exhaust valves and three inlet valves. All five valves are similar in size. This design allows for excellent breathing. And, as every valve is small, high (RPM) and very high power outputs are theoretically available. Although, compared to a four-valve engine, a five-valve design should have a higher maximum (RPM).
Valve problems are something you should not ignore. Because, they can turn into even more serious and expensive problems down the road. However, they are easy to prevent or at least delay, with proper engine maintenance. Finally, have your oil changed regularly. And, fix any other engine problems promptly.
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