For stock gasoline engines, some type of one or two-piece stainless steel alloy is typically used for original equipment valves. The exhaust valve has to withstand much higher temperatures than the intake valves so they are usually made of a stronger high temperature alloy.
Advertisement Most aftermarket performance valves are N or N stainless alloys, although some suppliers also offer a N alloy valve or their own proprietary alloy for high temperature exhaust valve applications. The higher the nickel content, the more expensive the alloy, and the more heat it can safely handle in a demanding racing environment. Valves made of N can handle temperatures up to degrees F. Advertisement For more demanding applications engines with nitrous oxide, turbochargers or superchargers , a higher temperature super alloy such as Inconel or Nimonic 80A could be used.
One aftermarket cylinder head supplier told us that they use N intake and exhaust valves in all of their cylinder heads from street performance to all-out big block race heads. Titanium reduces the mass of the valve by nearly 40 percent, which means you can use much less spring pressure for the same engine speed, or more RPMs using the same springs as before.
Reducing the weight of the valves increases spring life, and reduces the stress on the rockers, pushrods, lifters, cam and cam drive.
How well do titanium valves hold up? For wear resistance, titanium valves may be coated with a variety of materials including yellow titanium nitride TiN , moly or chrome nitride.
The coatings reduce friction, help dissipate heat and improve the surface hardness and wear resistance of the valve. Titanium valves tend to hold more heat than stainless steel valves so they require upgrading the seats to some type of copper alloy. Copper provides good thermal conductivity to pull heat out of the valve when the valve is closed. For many years, copper-beryllium alloy seats were used with titanium valves. Even so, beryllium dust is dangerous and requires special precautions when machining seats.
Using a cutting oil or coolant is recommended along with an OSHA-approved dust mask. Advertisement In recent years, beryllium-free copper alloys that contain extra nickel and silicon have been developed that deliver the same performance without the health risks.
Moldstar 90 is a beryllium-free copper alloy that can be used with ANY type of valve titanium or stainless or any fuel where high heat transfer is desired. To improve cooling, the hollow stems on exhaust valves may be partially filled with sodium.
This helps pull heat away from the head of the valve for longer valve life and greater reliability. It also allows the engine to handle more heat and spark advance. If a sodium-filled valve is cracked and is placed in an aqueous cleaning tank, the sodium may fizz out of the valve or even make the valve pop and crack in two. Some have blamed the problem on a quality control issue with the valve manufacturing process. There are photos of valves that have been cut open that reveal the center hole was drilled considerably off-center resulting in inconsistent wall thickness with one side being much thinner than the other.
Some of the hollow stems also show scoring inside from the drilling process, which creates stress risers that can lead to cracks and valve breakage. Others have blamed the valve failure problem on valve seat concentricity issues, excessive valve guide wear or poor control of stem-to-guide tolerances from the factory.
Excess guide clearance allows the valve to wobble and flex with every valve cycle. Some Corvette owners have replaced their stock guides with aftermarket bronze valve guides. Advertisement In diesel engines, Stellite faced valves are often used to handle high exhaust temperatures. Stellite may also be used on the intake valves, too. Stellite is a cobalt and chromium alloy that increases the surface hardness of the valve face to about 55 to 59 Rockwell C.
A thin coating is applied to the seat area of the valve and valve tip the valve is usually a N stainless alloy or similar material.
The Stellite coating greatly improves wear resistance at high temperatures. If you are rebuilding a diesel engine that is factory-equipped with Stellite faced valves, use the same type of replacement valves, never ordinary valves.
Valve seats have to be compatible with the type of valves in the engine. With most cast iron heads, the seats are integral and induction-hardened for wear resistance.
With aluminum heads, the seats may be some type of cast iron alloy, powder metal or high copper for high temperature performance engines or titanium valves. Advertisement Valve seat suppliers offer a variety of seat materials, so work with your supplier to determine which alloy is best for the engine you are building. A high chrome alloy iron alloy with a Rockwell hardness of RC40 should be more than adequate for your typical unleaded fuel gasoline engine, stock or performance.
This type of alloy holds up well in applications with exhaust temperatures up to degree F. For natural gas or propane fueled engines, or turbocharged, supercharged or nitrous motors, a higher temperature nickel-based alloy would be recommended. Such a material can handle exhaust temperature up to degrees F.
Advertisement For applications where additional high temperature wear resistance is required like a heavy-duty diesel , a Stellite faced seat alloy might be required. Moving on to powder metal PM seats, these are used as original equipment in many late model gasoline and some diesel engines. The car makers like PM seats because they are less expensive than alloy seats, can be molded close to finished dimensions, and are easy to machine when new.
The operation is controlled by pear-shaped lobes, called cams, on a rotating shaft, the camshaft , driven by a chain, a belt, or a set of gears from the crankshaft. Where the camshaft is mounted in the engine block , small metal cylinders tappets sit in channels above each cam, and from the tappets metal pushrod extend up into the cylinder head. The top of each pushrod meets a rocker arm which bears against the stem of a valve, which is held in a raised closed position by a strong coiled spring the valve spring.
As the pushrod rises on the cam it pivots the rocker arm, which pushes the valve down open against the pressure of its spring. As the cam lobe rotates further, the valve spring acts to close the valve. This is called an overhead-valve OHV system. Some engines have no pushrods; the valves are operated more directly by single or double camshafts in the cylinder head itself the overhead-cam system. As there are fewer moving parts between the camshaft and the valve, the overhead-cam OHC method is more efficient and produces more power for a given engine capacity than an engine with pushrods, because it can operate at higher speeds.
With either system, there must be some free play in the operating gear, so that the valve can still close completely when parts have expanded through heat.
A pre-set gap tappet clearance is essential between the valve stem and the rocker arm or cam, to allow for expansion.
Tappet clearances vary widely on different cars, and faulty adjustment can have serious effects. If the gap is too large, the valves open late and close early, reducing power and increasing engine noise.
Whether it be Car, Commercial, Plant or Marine. We only supply quality gaskets that match the OEM specification or even exceed it. We have stock of a wide range of pistons and piston rings whether they are standard or oversized. We have a good range of belts, belt kits, chains and chain kits on a same or next day basis. We have a massive range of valves and guides on our shelves for European and Asian motors. Components are also available for vintage and classic cars by special request.
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We are dedicated to the engine parts sector and the majority of our team have been with us since we started in We offer a same-day delivery service to exclusive areas of England on our internal van service. Please see our information page for more details. We only stock components from the World's leading brands. All of our parts have a minimum of 12 months of manufacturers warranty and are of OEM standard or higher. We have built our reputation over the years by selling good quality products at a very competitive price with fast and reliable delivery.
Our range of Engine Parts manufacturers from all over the World. We do not list specific parts on our website, we have thousands of parts in stock. If you are looking to purchase specific parts, please call or use the webform. Skip to main navigation. Broken or bent valves are the result of piston contact if the engine timing is incorrect Valve Guides A valve guide is a narrow tubular piece of metal that can be made from cast iron, Bronze or other composite alloys. Tappet Shims We stock a wide range of shims in different sizes.
Freccia Valvetrain. EP Valvetrain. AE Valvetrain. Excessive valve stem and guide wear. Valve head breaking off stem. Inlet valve underhead carbon build-up. Stem breakage through collet groove. Blow hole through valve head, starting from a radial crack.
Valve Breakages — Fracture at lower cotter groove. Engine Bearings More details Engine Bearings We have a massive range of bearings for same or next day delivery. Technical Support If you can't find what you are looking for or would like any advice on what components you may need, our experienced sales staff are happy to help. Fast Delivery We offer a same-day delivery service to exclusive areas of England on our internal van service. Quality We only stock components from the World's leading brands.
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