Automotive Engine Valves – Function – How They Can Fail – Testing

Automotive Engine Valves Leaking
Automotive Engine Valves Leaking

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.

(OHV) Engine Valves Are Operated By Pushrods
(OHV) Engine Valves Are Operated By Pushrods

An overhead camshaft engine (OHC); needs fewer parts to operate the valves. The camshaft operates directly on bucket tappets.

(OHC) Engine Valves Run On Buckets
(OHC) Engine Valves Run On Buckets

This is why the automotive engine valve plays 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.

Automotive Engine Valves
Automotive Engine Valves

Damaged Automotive Engine Valves Can Result In;

  • Reduced power
  • Poor fuel consumption
  • Complete engine failure

Any valve will eventually wear out if driven enough miles. But many valves call it quits long before they should; because of burning or bending.

Burnt Valves

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.

Burnt Exhaust Valve
Burnt Exhaust 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. Consequently, They operate at a much cooler temperature.

Bent Valves

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.

Bent Valves
Bent Valves

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, The intake and exhaust valves rely on physical contact with the valve seat and guide for cooling. The combustion heat is conducted away through the valve seat and guides.

Machining Valve Seats For Proper Contact
Machining Valve Seats For Proper Contact

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

Testing For Leaking Valves
Testing For Leaking 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 leak.

How Many Valves Can You Have

A multi-valve engine design typically has three; four; or five valves per cylinder to achieve improved performance.

Multiple Valves
Multiple Valves

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); 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 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.

Conclusion

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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