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Your Valve stem seals worn out? » Read more about common malfunctions • Repair • Replacement manual
Keep the combustion chamber pure with the valve stem seal
The valve stem seal, or "stem seal" for short, seals the camshaft along the tracks of the valve stems. This prevents oil from the camshaft getting inside the combustion chambers. Replacing the stem seals is expensive, but can also be performed by laymen, provided they have a little patience and the right tools. However, a few important steps must be taken.
Valve stem seal position and function
The valve assembly consists of the steel valve itself, the stem seal, the return spring and the valve disc. The valve opens when the camshaft presses against the valve disc directly, or indirectly via a hydraulic tappet. Once the cam that moved the valve has passed by, the spring pushes valve back into its closed position. The valve stem seal is a so-called "shaft seal". This consists of a thick cylinder made of hard rubber with a hole inside. The hole is provided with an inner lip. This lip is mainly responsible for the sealing performance of the valve stem seal. After a few thousand kilometers, the valve's rapid back and forth movement can gradually wear the stem seals. Overheating and lack of lubricating oil are particularly damaging to stem seals.
Detecting stem seals defects
If the valve stem seal is damaged, lubricating oil makes its way into the combustion chamber. The burning of the lubricant becomes noticeable by bluish smoke in the exhaust gas. However, lubricating oil can also reach the combustion chamber if the piston rings are defective. With defective stem seals, however, the tell-tale blue smoke is most likely to occur when the engine is cold. Once the valves have reached their normal operating temperature, they may have expanded sufficiently to restore the full sealing performance. Broken piston rings, however, constantly cause blue smoke.
Nonetheless, this distinction is not absolutely reliable. Therefore, it is common to begin by changing the stem seals if the characteristic blue smoke appears from the exhaust. This is much simpler, cheaper and less time-consuming than replacing the piston rings.
With turbocharged engines it is particularly important not to postpone the repair of oil being burned in the combustion chamber. Otherwise, drivers risk damage to the turbocharger, because the heavily oil-containing exhaust gas deposits. The catalytic converter is also at risk of taking damage if oil is being burned. Furthermore, oil combustion means that the oil fill level continuously decreases and needs to be checked frequently.
Repairing a valve stem seal
Usually the stem seal is replaced with the cylinder head removed. Yet, with a little skill, it can also be done with the head in place.
To replace the stem seals, the valve cover and possible also the camshaft must be removed. This is usually required if the engine is not controlled via hydraulic valve lifters. If the hydraulic valve lifters were removed, it is very important to install them in the same order they were previously removed in upon completing the repair. To ensure this is done, stick the hydraulic valve lifters through a piece of cardboard and number them. Removing the camshaft also requires the timing chain or timing belt to be removed. This is a great opportunity to replace the timing belt, too, and save an interval. A timing chain can also stretch over time. Therefore, its replacement is also indicated when replacing the stem seals.
If the camshaft has been removed, the valve disc and the valve spring are pulled out with a pair of pliers. For this, the spring tension must usually be relieved with a special tool. The connection between the valve and valve disc usually consists of wedges that can be pulled out with a magnet. The trade offers special tools for pulling of valve stem seals. These tools significantly simplify the task at hand. One must make sure that the valve does not fall into the combustion chamber during removal. The trade offers special tools, which keep the valves in place by means of a permanent supply of compressed air. These tools may also be rented.
After installing the new stem seals and reassembling all components, the valves must be set again. Here, a feeler gauge and the values from the repair manual will help perfectly tune the engine.
Quality valve stem seals by a brand manufacturer
Although valve stem seals are difficult to install, they are very inexpensive to purchase. Brand manufacturers like FEBI BILSTEIN rarely charge more than 1 euro for a new stem seal, usually even less. Therefore, it makes no sense to opt for a product by an unknown manufacturer.
