What Is A Valve Seat?

What Is A Valve Seat
Valve seats in exhibition. The valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. The valve seat is a critical component of an engine in that if it is improperly positioned, oriented, or formed during manufacture, valve leakage will occur which will adversely affect the engine compression ratio and therefore the engine efficiency, performance ( engine power and engine torque ), exhaust emissions, and engine life.

Valve seats are often formed by first press-fitting an approximately cylindrical piece of a hardened metal alloy, such as Stellite, into a cast depression in a cylinder head above each eventual valve stem position, and then machining a conical -section surface into the valve seat that will mate with a corresponding conical section of the corresponding valve.

Generally two conical-section surfaces, one with a wider cone angle and one with a narrower cone-angle, are machined above and below the actual mating surface, to form the mating surface to the proper width (called “narrowing” the seat), and to enable it to be properly located with respect to the (wider) mating surface of the valve, so as to provide good sealing and heat transfer, when the valve is closed, and to provide good gas-flow characteristics through the valve, when it is opened.

  • Inexpensive engines may have valve seats that are simply cut into the material of the cylinder head or engine block (depending on the design of the engine).
  • Some newer engines have seats that are sprayed on rather than being pressed into the head, allowing them to be thinner, creating more efficient transfer of heat through the valve seats, and enabling the valve stems to function at a lower temperature, thus allowing the valve stems (and other parts of the valvetrain ) to be thinner and lighter.

There are several ways in which a valve seat may be improperly positioned or machined. These include incomplete seating during the press-fitting step, distortion of the nominally circular valve seat surfaces such that they deviate unacceptably from perfect roundness or waviness, tilt of the machined surfaces relative to the valve guide hole axis, deviation of the valve seat surfaces from concentricity with the valve guide holes, and deviation of the machined conical section of the valve seat from the cone angle that is required to match the valve surface.

What does a seat do in a valve?

Valve Seat – The valve seat is a surface inside the body of a valve that comes into contact with the disk, which is a moveable component that restricts and allows flow through the valve. It has several important purposes, including the following:

  • Preventing compressed or combustion gasses from getting into the manifold.
  • Permitting a particular amount of heat to travel through the valve to the cylinder head.
  • Maintaining the proper seal of a mounted valve.
  • Reducing wear-resistance by resisting pressure and high heat.

What does it mean to drop a valve seat?

In car engines, an engine valve that is said to have dropped refers to a valve in the cylinder head of the engine that has usually broken off at the stem that connects the valve to the rod.

Where is the valve seat in an engine?

Lori Kilchermann Date: August 19, 2022 Woman posing The valve seat is the area in an internal combustion engine’s cylinder head that the intake and exhaust valve actually contact when the valve is in the closed position. Typically made of a special alloy such as Stellite™ or a tungsten-vanadium compound, the valve seat is commonly pressed into the cylinder head and machined to allow for maximum flow and sealing of the intake and exhaust gasses.

  1. Both cast iron and aluminum cylinder heads use a valve seat to provide the proper valve closing and sealing of the combustion chamber.
  2. Most valve seat machining consists of multiple angles machined on both the seat and the valve head to create both flow and pressure sealing.
  3. Most original equipment engines are designed to run on unleaded or diesel fuel, while the typical performance engine is commonly fueled with unleaded racing gasoline or methanol.
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Unleaded gasoline does not provide the cushioning effect the leaded fuel provides. This can lead to a valve seat being destroyed by the tremendous forces of the valves being opened and slammed closed. In leaded fuel, the lead is used to cushion this force and provide long-term protection for both the valve and the valve seat.

  • Some engine builders recommend a lead substitute be added to the unleaded fuel to protect the valve train,
  • The uses of special alloys in the manufacture of the valve seat allow the component to operate on unleaded fuels while resisting the destructive forces caused by the rapidly opening and closing of the valves at high speed.

Along with the hammering effect of the valves, extreme heat is also a force to be combated in designing a durable valve train. The harsh environment the valve seat operates in makes alternative cooling by air or oil impossible, so the seat must rely only on the alloy used in its construction to provide operational protection.

When installing a seat into a cylinder head, a hot and cold system of interference fit is often used. By heating the cylinder heads, the machined opening for the seat expands as the material in the head expands. The seats are often placed into a freezer to shrink the molecules in the component and make the seat as small as possible.

The frozen valve seat is then pressed into the hot head and allowed to come to an even temperature. The result is a very tightly-fitted seat that will remain in place while being machined, operated and maintained.

What is valve seat in automotive?

The Valve Seat is the seat of the engine valve. It contacts the exhaust valve and maintains airtightness of the combustion chamber. Our Valve Seat uses material with hard particles are dispersed onto it, using a specialist alloy dust developed by us, which has a superior balance of heat resistance, friction resistance and compatibility with valves, and can support 4-wheel and 2-wheel vehicles for diesel, gasoline or gas fuels such as LPG and CNG.

What causes valve seat damage?

Possible causes include an incorrectly set valve clearance − or the valve seat insert or valve guide were not remachined centrically. An excessively large or small valve guide clearance can also have fatal consequences.

Why do engines drop valves?

John NW Ia
Posted 5/5/2008 22:39 (#372116) Subject: What causes a dropped valve?

/td> Pocahontas, Ia My 8440 engine dropped a valve today. Developed a loud knock after about 45 mins. in field – was warmed up properly. Unfortunately, hired help drove it to the end. Service man came out and drove it some more. Thought a bad injector as blue smoke out the exhaust. Had us drive it to shop. No compression in # 5. Pulled head and found dropped valve. Took piston and sleeve, maybe more. I assume I need to replace the turbo. This engine was completely overhauled about 550 hrs. ago with new crank and cam, rebuilt pump and turbo. What can cause a valve to “drop” ? Thanks edit: What can I expect to receive from a salvage yard for this anchor? It has 8 decent 18.4X38 tires (90% ) Edited by John NW Ia 5/5/2008 22:44 DBH

Posted 5/5/2008 23:27 (#372174 – in reply to #372116) Subject: RE: What causes a dropped valve?

/td>

Eastern Washington Don’t know about your dropped valve, I just know I’ve put the last dollar I’m going to put in my 8650, sitting in my yard with another broken crank. The salvage guy’s told me $2500 and my tires aren’t much, I told them to come and get it, they haven’t showed up in 6 months, hope they haven’t changed there mind, LOL John NW Ia
Posted 5/5/2008 23:51 (#372200 – in reply to #372174) Subject: Broken crank was reason for last overhaul

/td> Pocahontas, Ia Broken crank was reason for last overhaul. Biggest reason for doing OH then was I just spent BIG $$$ adjusting end play on all 4 axles. EJB ( SK )

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Posted 5/6/2008 00:03 (#372215 – in reply to #372116) Subject: RE: What causes a dropped valve?

/td> Was the spring broken? Neighbour lost his 4450 last year from same problenm.

What happens when engine valves fail?

Burnt valves – The other common type of valve failure is valve burn, or burnt valves. Essentially this is caused by combustion gases escaping between the valve and valve seat when they are not sealing correctly. The hot combustion gases are forced past the valve which starts to burn away the edge of the valve, progressively getting worse the longer it is left without being rectified.

How much does it cost to replace a valve seat?

The most expensive part of a valve job is the labor. It can take up to 7 hours to complete the job correctly, meaning each piece is resurfaced, the seats are drilled out, and the valves reseated. Labor can cost between $70 and $150 per hour, meaning you could expect an average of $770 for labor alone.

Do valve seats need to be replaced?

When do I need to replace my valve seats and valve guides? – Valve seats should be replaced when they are pitted, chipped, or too damaged to re-cut. Seat replacements are also necessary when they have been cut multiple times and are now too deep to set proper valve clearance.

Can valve seats be repaired?

Home, Automotive Repair Library, Auto Parts, Accessories, Tools & Equipment, Manuals & Books, Car BLOG, Links, Index Copyright AA1Car Adapted from an article written by Larry Carley for Engine Builder magazine Replacing valve seats is one of the basic jobs that is often necessary when rebuilding aluminum or cast iron heads with cracked, damaged or badly worn seats.

But there is a lot more to replacing a valve seat than prying out the old one and driving in a new one. If the head is cast iron with integral seats, the head has to be machined to replace the seat (sometimes called installing a “false” seat). And if the head is aluminum, the seat counterbore may have to be machined to accept an oversize seat if the bore is loose, deformed or damaged.

Either way, a machinist has to figure the amount of interference that is required for the new seat before cutting the head on a seat-and-guide machine. He also has to decide what type of seat to install. Replacing a seat, therefore, involves a number of decisions and steps, all of which affect the outcome of the repair job.

  1. As you might have guessed, we encountered differing opinions about the right way and wrong way to replace valve seats while researching this article, particularly with respect to the amount of interference fit that is required to retain seats in aluminum heads.
  2. A common fear expressed by many engine rebuilders is concern over the possibility of seats falling out, particularly in aluminum heads where the difference in coefficients of thermal expansion between the head and seats can cause seats to loosen if the head overheats.

Consequently, engine rebuilders expressed differing views on whether or not locking compound and/or peening or staking should be used as “insurance” when installing seats in aluminum heads. One point everyone does seem to agree upon is that valve seats play a critical role in the longevity of the valves.

The seats draw heat away from the valves and conduct it into the cylinder head. This provides most of the cooling that the valves receive and is absolutely critical with exhaust valves. Anything that interferes with the seat’s ability to cool the valves (such as a loose fit or deposits between the seat and its counterbore) can lead to premature valve failure and expensive comebacks.

The seat alloy and hardness must also be matched to the application and compatible with the type of valves that are installed in the engine. Again, we found differences of opinion regarding the selection and use of various seat materials. To better understand the issues behind the differing opinions regarding valve seat replacement, let’s start with the seats themselves and why they fail.

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What are the two types of valve seats?

Like valve guides, there are two types of valve seats – integral and insert. Integral seats are part of the casting. Insert seats are pressed into the head and are always used in aluminum cylinder heads. Most pre-1978 integral seats are soft cast iron.

What is valve seat test?

Types of valve leakage tests – The tests that must be conducted depend on the type of valve and, therefore, the valve elements. Below are some of the most commonly performed tests of valve leakage.

  • Valve seat leakage tests are required for pressure relief valves.
  • Backseat tests are required for valves with a backseat element, including gate and globe valves.
  • Closure tests are required to test the closure mechanism of several types of valves, including gate, globe, plug, check, and ball valves.
  • Shell leakage tests are required for valves that are used in “full open” and “full closed” service, such as check, stop, and isolation valves.

Visit our Resources page for links to the applicable performance standards and tests required for different types of valves. Contact us for more information about our preventative maintenance services and programs.

What is a valve seat in a faucet?

How Do You Know if it’s a Bad Valve Seat? – Fortunately, a bad valve seat is relatively easy to identify. First, it helps to have a good understanding of what the valve seat actually is. It is located at the base of the device that’s used to turn the water on and off.

The washer that opens and closes to allow water through is seated directly on top of the valve seat. If the issue with your faucet is a bad valve seat, you are likely to encounter issues with water dripping from around the handle area. The leak may occur whether the faucet is on or off. When this is the case, it is time to call in a plumbing pro to replace your valve seat so you can stop losing water.

Replacing a valve seat can be a bit tricky, even for handy homeowners. It may require specialty tools like a seat wrench, valve seat grinder, and/or dresser. If you cannot locate a valve seat that is an exact match for what you have, you may need some of these other tools to help reshape the bad valve seat and stop the leak.

What is a tap seat?

Tap Seat: The Tap Seat is the flat, smooth surface inside the tap body that the tap valve seals against. Damage to the Tap Seat through repeated use is often a contributing factor to a leak, as the tap valve is unable to make an effective seal.

Can valve seats be replaced?

When do I need to replace my valve seats and valve guides? – Valve seats should be replaced when they are pitted, chipped, or too damaged to re-cut. Seat replacements are also necessary when they have been cut multiple times and are now too deep to set proper valve clearance.

What is valve seat test?

Types of valve leakage tests – The tests that must be conducted depend on the type of valve and, therefore, the valve elements. Below are some of the most commonly performed tests of valve leakage.

  • Valve seat leakage tests are required for pressure relief valves.
  • Backseat tests are required for valves with a backseat element, including gate and globe valves.
  • Closure tests are required to test the closure mechanism of several types of valves, including gate, globe, plug, check, and ball valves.
  • Shell leakage tests are required for valves that are used in “full open” and “full closed” service, such as check, stop, and isolation valves.

Visit our Resources page for links to the applicable performance standards and tests required for different types of valves. Contact us for more information about our preventative maintenance services and programs.