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An Automotive Service and Repair Industry |
Educational ResourceRegarding the Technical Topic of: |
O-Ring Valve Stem Seal |
The Valve Stem Seal— Theory, Design, Diagnostic and Replacement —An automotive technical article written by John HarloweDate of Publication: 2015-07-18Copyright 2015Moonlight Engineering Automotive Fabrication and Design Company |
Umbrella Valve Stem Seal |
In this automotive technical article the following subjects are discussed: the theory as to why a valve stem seal is needed for the valve guide, the design and material composition variations of the valve stem seal, the diagnostic methods used in determining the cause of valve stem seal failure and “ how-to ” replacement procedures for the different types of valve stem seals. |
A valve stem seal is very small relative to other gaskets and seals required in an engine, however the function of this seal is vital for proper valve train lubrication. What is it about the valve stem seal that makes it different than almost every other type of seal in an engine? The short answer is that a valve stem seal is designed to “ leak. ”The answer to this question may seem, at first, to be counter-intuitive, however when one considers the fact that zero clearance between the valve and it's guide is an impossibility , a seal engineered to precisely deliver, i.e., leak, a specific amount of oil for valve stem lubrication makes perfect sense. However, as one can imagine, the diagnostic procedure determining whether or not a “ leaking ” seal functions within it's designed parameters is a unique and, at times, a tedious one. |
According to numerous Automotive Service and Repair Industry research studies, along with my on-going repair trend study utilizing data from IdentiFix records, nearly half of all customer oil consumption complaints were resolved by the replacement of the valve seals. |
IdentiFix gives me access to over 600,000 repair archives the archive base expands by approximately 1,500 repairs per week. |
That being said, let's take a look at the engineering behind the cylinder head design in the internal combustion engine and the processes that lead to valve seal failure.FIGURE 1FIGURE 1: The design of an internal combustion engine, operating within it's normal parameters, creates a low pressure vortex in the valve chamber during the intake stroke of the combustion cycle; this vortex “ suction ” effect increases the oil intake into the valve guide. Unable to be completely diluted by the air / fuel mixture, this additional oil then is only partially burnt in the cylinder when the fuel ignites, with the remainder, of course, exiting the exhaust system in the form of smoke. The valve stem seal functions to reduce additional oil intake into the valve guide. |
FIGURE 2The exhaust guide can cause oil consumption via the atomizer effect, i.e., due to a faulty valve seal, the exhaust gas moving past the exhaust valve causes a vacuum that pulls oil down the guide and into the hot exhaust. |
FIGURE 2: Under normal operating conditions, the engine's exhaust produces smoke through oil being burned by the combustion process, on newer vehicles, say vehicles having 50,000 miles or less on the odometer, the stoichiometric air-fuel mixture [ 14.7 parts air to 1 part fuel ] dilutes the minute traces of oil that leaked in, making this “ smoke ” virtually invisible to the human eye. During deceleration, when the throttle is closed, there is not enough fuel available for the escaping particles of oil to be diluted by, regardless, on a newer vehicle this burned oil will remain invisible to the human eye because the oil leakage into the combustion chamber is less than ten parts per million. On older, high mileage vehicles, smoke from the exhaust when decelerating, can usually be seen with the human eye. This deceleration smoke is a telltale diagnostic sign of worn valve guides and or the valve guide seals. The next time you are driving down a long grade, notice how many cars in front of you have exhaust smoke. These vehicles engine's are probably using oil through the valve guides. Oil leakage past the valve guide seals is a more likely cause of oil consumption than leakage past piston rings. |
FIGURE 3Carbon deposits are a very poor heat conductor, the fuel vaporization process eventually will become less and less effective and, as a consequence, will reduce individual cylinder combustion efficiency, waste fuel, decrease performance and create undesirable emissions. |
FIGURE 3: Worn valve seals can cause carbon buildup on the valve stem and such buildup disrupts volumetric efficiency [ the engine's breathing ability ], by altering the flow pattern of the air-fuel mixture engineered into the OEM cylinder head design, and this turbulence decreases engine power. When only one side of a spark plug is fouled with carbon, leaking guide seals are indicated. The carbon will be on the side of the spark plug that was facing the intake valve. Leaking valve guide seals also result in carbon deposits on intake valve necks. |
FIGURE 3AHeavy carbon deposits on the valve and very little on the piston is an indication of a faulty valve stem seal. |
FIGURE 3BA boroscope diagnostic eliminates the need, and expense, for an engine tear-down inspection because the boroscope gives an internal view of a cylinder including the piston, cylinder walls and valves. Can be used to verify head gasket failures, bent valves, sludge accumulation and other serious problems. |
FIGURE 4Valve stem seals play a critical role in controlling valve lubrications well as oil consumption. If the seals do not fit properly or are not installed correctly, the guides may be either starved for lubrication or flooded with oil. Either way, the engine is going to have problems. |
There are three types of valve guide seals: umbrella, positive, and O-ring [ see Figure 4 ]. Most engines today use a positive valve guide seal attached to the top of the valve guide. The valve moves up and down inside of it. Overhead cam engines use positive seals because the camshaft is heavily lubricated right above the valves. Positive seals are also used on late-model cam-in-block [ pushrod ] engines.The umbrella seal, used on many older engines, fits snugly over the valve stem. It rides on the valve stem as it moves up and down, preventing oil from entering the valve guide.The O-ring seal was used on many millions of older General Motors engines. It fits under the keepers, inside of the spring retainer. Oil is pumped through a hollow pushrod to a hole in the rocker arm where it spills onto the valve spring retainer. Without the O-ring seal, oil would be able to leak down the stem and into the guide.Valve guide seals can be made of several different types of materials having varied resistance to temperature. High engine operating temperatures cause lower grade materials, such as nitrile, to harden and become brittle over time. Eventually, this can lead to cracking, loss of oil control and seal failure. When a valve stem seal loses its ability to control the amount of oil that enters the guide, it can cause a variety of problems.Although most kinds of artificial rubber look and feel alike, they are not. The premium seals resist heat up until about 440°F. Lower quality seals resist heat only to 250°F. At the combustion chamber end of the exhaust valve stem, the valve temperature is in excess of 1,300°F; resistance to temperature is important. Premium Viton and Teflon seals are used for the highest temperature applications using positive valve guide seals.Water jackets are cast in the cylinder head behind the valve seat and around the valve guide. Heat from the valves is transferred from the valve stem to the valve guide and finally into engine coolant. Vehicle Maintenance TipMaintain a clean, efficient flowing cooling system so the engine does not exceed it's designed temperature operating range. |
FIGURE 4A — shows a photograph of a cross-sectioned cylinder head with white arrows pointing to the water jacket coolant flow tunnels.FIGURE 4A1 — shows a line drawing cross-sectioned cylinder head with red arrows revealing how the heat from the valve and valve guide are dissipated by the coolant flowing through the water jackets.Lack of Engine Maintenance WarningA poorly maintained cooling system will develop rust, scale and or sediment deposits in the water jackets thereby impeding coolant flow resulting in higher than normal engine operating temperature.Cause and Effect RelationshipWhen one automotive engine sub-system is not maintained, the neglect will cause a domino effect upon other engine systems and, eventually, engine failure is the resulting effect. |
FIGURE 4B |
The combustion chamber experiences severe operating conditions. Valves are heated to very high temperatures as they open and close at half crankshaft speed. Exhaust valve seats run at about 800°F, but the operating temperature at the neck of exhaust valves can exceed 1,300°F. This is above the melting temperature of aluminum and it is red hot for steel valves. The intake valve runs at a temperature between 700°F and 1,000°F. It operates at a cooler temperature than the exhaust valve because it is sprayed with a relatively cool bath of air and fuel during every intake stroke. |
FIGURE 4CFIGURE 4C: Valve stem seals provide a controlled leak of oil to allow the valve stem to be lubricated as it slides in the valve guide. The amount of oil that passes by the valve stem seal must be precisely controlled, as too little oil causes stem and guide wear. Too much oil causes carbon buildup leading to valve seat damage, decrease in volumetric efficiency, increased emissions and excessive oil consumption. |
VALVE STEM SEAL INSTALLATION“ How-To ” Procedures, Techniques and Tools |
NOTE: Before installing positive seals, remember to install the valve spring shim, if applicable. |
FIGURE 5 — O-ring type valve stem seal.FIGURE 5: O-Ring Type of Valve Seal. Sometimes intake and exhaust seals are made of different materials or have different shapes. Always check for instructions in the gasket set regarding the placement of these seals. |
Be certain to lubricate the valve stem seals before installing them. By the time the engine's oil splash lubrication reaches the valve stem seals, they will most likely become heat-hardened and brittle during the engine's normal warm-up process. |
FIGURE 6 — Valve spring compression tool shown with air-hold installed in cylinder.FIGURE 6: Valve guide seals can be replaced without removing the head. Air is put into the cylinder to hold the valve while the spring is compressed. Using a spring compressor, compress the spring / retainer assembly until the 2nd groove of the valve stem is exposed, now put an o ring on the stem end and using a small pick push the o ring into the 2nd groove, install the 2 lock halves, then release the spring compressor. |
An Automotive Repair Do-it-Yourself Help TipWhen compressed air is not available to hold the valve against its seat, a good substitute for the air is to put a piece of rope, while the piston is below TDC, through the spark plug opening into the cylinder you want to remove the valve spring from. Then turning the crankshaft by hand, bringing the piston up towards TDC, will then force the rope between the piston and the head of the valve, thereby wedging the valve against its seat. The rope is easily removed when the job is completed. |
FIGURE 7FIGURE 7: Positive Type of Valve Seal. Positive seals are sometimes supplied with a plastic sheath that is installed over the tip of the valve stem to cover the valve lock grooves and protect the sealing surface on the inside of the seal. A positive valve stem seal provides a tighter choke which reduces the amount of oil that enters the guides. This minimizes oil consumption and hydrocarbon emissions and also helps to keep intake vacuum high for better idle quality. |
A client of mine did a RestoMod on a 3rd generation El Camino, that he's owned since new, having under 100K miles on the odometer. The engine, along with the rest of the drivetrain, was in good condition. The small block was a strong runner that did not smoke or use oil, however my client wanted to do through it just the same. Basically he did a complete engine re-gasket, including head gaskets, but no bearing or rings; he wanted to take care of the minor engine oil seepage he had and re-paint the factory color. The task was something he felt comfortable doing in his home garage with his expertise level. After the Camino was done he went on a shakedown road trip and noticed the engine was using oil like never before. He had to put in 2 quarts of oil in his 500 mile round trip journey.So when he returned from his trip he called me and set up a time to bring the Camino so I could do a diagnostic on it, other than the excessive oil consumption the Camino ran like a champ, so he was at a loss as to what the problem could be. Long story made short: when I pulled the spark plugs to gauge the combustion efficiency, I noticed all the spark plugs had carbon deposits on just one side of the center insulator, indicating to me that there was a valve stem seal issue. With compressed air injected into the spark plug holes, I removed the valve springs on each cylinder to inspect the valve stem o-ring seals. I found that every o-ring was twisted on each of the valve stems and this was the cause of the excessive oil consumption effect. The only way this could happen is if the o-rings had been put onto the valve stem before the spring was installed, and after speaking to my client, he confirmed that is exactly what he did; admiting he did not refresh himself on that operation even though he had the factory service manual on his workbench. |
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John HarloweOwner: Moonlight Engineering Automotive Fabrication and Design CompanyNorth American Industry Classification System number 811121: restoration, antique and or classic automotive shop.Bachelor of Science in Business Administration from Humboldt State University 2010 |