Engine Valves & Components

Intake & Exhaust Valves, Valve Springs, Guides, Seats & Seals

Valves allow gases to flow in and out of the cylinders, and seal the combustion chambers so compression can develop. They open and close in response to the lobes on the camshaft via the valvetrain mechanism. The air/fuel mixture flows in when the intake valve opens, and the spent exhaust gases flow out when the exhaust valve opens after the power stroke. Every engine has at least one intake and exhaust valve, while many have a pair of each.

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A valve has a round disc called the head attached to a long shaft called the stem. On the perimeter of the head is a machined surface called the face that seals against a machined seat on the cylinder port. The stem reciprocates inside a tube in the cylinder head known as the valve guide. The top of the valve stem is attached to a retainer that fits over the valve spring, which encircles the valve and returns it to the closed position after opening.

The most common valve failure is overheating, especially on exhaust valves, which causes the valve to “burn” and distort and/or crack. The exhaust valve is exposed to extreme temperatures, and the valve must be able to seat fully to transfer this heat to the cylinder head. Carbon buildup, incorrect valve adjustment, or any other factor that keeps the valve from seating will prevent heat transfer. A burnt valve will not be able to seal the combustion chamber, causing reduced compression and power from that cylinder. Some performance engines have sodium filled exhaust valves to help reduce their temperature.

Worn valve guides are another problem that can develop and the excess stem-to-guide clearance can cause further problems. Guides locate the valve face on the seat, and worn guides can cause less than perfect sealing with loss of compression and power. The guide is another are where heat transfer takes place and a loose exhaust guide can also be cause for exhaust valve failure. A worn intake guide can allow unmetered air into the intake port, causing a lean condition and engine misfire. And excessive clearance can allow oil to be drawn into the combustion chamber, causing reduced performance and oil consumption.

Miles and engine heat can also take their toll on valve springs. The valve springs must have enough pressure to keep the valves closed and maintain valve lash. Seat pressure is usually 70-90 lbs. on a stock engine with open pressure at 200 lbs. or more. Weak valve springs can’t exert the proper amount of pressure, which can cause misfire and loss of power as engine speed increases, resulting in “valve float”, where the valves fail to close. In extreme cases valve float can allow the valves to contact the pistons on some engines, bending or breaking the valves and cracking or breaking the pistons.

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Guides & Articles
This article will guide you through a generic tune up on most any car or light duty gasoline-powered vehicle built within the last 20 years or so. We will presume that you are tuning up your engine because it has reached the mileage or time point to do so, and that you are NOT performing a tune up to cure an engine performance defect. We make this distinction...
Internal combustion engines are extremely complex and feature a wide array of components that rotate, move up and down, pump, seal, or remain stationary. When repairing or rebuilding your engine, you will come across many different terms when referencing repair manuals and ordering parts. We know it can be confusing, especially when the repair is complex. Even if...
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Engine Valves & Components Reviews
Average rating:54.9 - 4 reviews
2000 Acura Integra
| Posted by | (Lakewood, NJ)

After doing some research I found these springs. I am so impressed their design. They enable my engine to rev freely to redline. Thank you for your job, guys!

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