Mar. 06, 2024
Valve stem seals are small components within your engine, however the role they play in the grand scheme of things is quite significant, relative to their size. In this quick guide, we’ll be discussing the importance of these integral parts, including what they are, how they work, symptoms of failure, along with what you can do to ensure their longevity and maintain your engine’s functionality.
Valve stem seals sort of go against the traditional meaning of ‘seal’, as they are actually designed to leak out oil- but in a controlled manner, of course. Chiefly, there are three different types of valve stem seals:
O-Ring Valve Stem Seals
You won’t find these valve stem seals in any modern engines, however it’s still good to learn that they exist. O-ring valve stem seals sit below the valve stem keepers and work by stopping oil from leaking between the valve stem and valve retainer.
Umbrella Style Valve Stem Seals
Umbrella style valve stem seals sit around the top of the valve stems and move up and down along with the valve, to protect the valve guide from any excess oil by deflecting it.
Positive Valve Stem Seals
Positive valve stem seals are what you’ll find in almost all modern engines built today. This is the most effective type of seal by far, and functions similar to that of a squeegee by wiping and metering the oil. The oil then lubricates the seal as the stem passes through.
A lot of oil runs through your engine, but it’s especially important that this oil does not enter the combustion chamber. Valve stem seals keep the crankcase and combustion chamber separate, so that oil does not enter the combustion chamber, and the oil within the cylinder head is prevented from being contaminated. They do this by controlling the amount of oil that enters the guide.
One of the most common signs of valve stem seal failure is increased oil consumption. So, if you notice that your oil is decreasing at a far more rapid rate than usual, you should ensure to take worn valve stem seals into account as a possible cause. On the other hand, engine oil leaks, excessive smoke or decreased acceleration power are also common symptoms that you may experience.
Valve stem seals often last hundreds of thousands of miles before they have to be replaced, however improper installation or infrequent oil and filter changes can contribute towards their faster deterioration. For this reason, it’s important to:
Trust in a Reliable Auto Mechanic
As valve stem seals can be installed incorrectly, it’s important to ensure that you’re bringing your vehicle to a highly reputable and reliable auto mechanic. This is especially true if you’re the owner of a luxury European vehicle brand; after all, you wouldn’t put your prized possession in the hands of just any old mechanic.
Keep Up with Frequent Servicing
When you subject your vehicle to frequent servicing, you will be allowing experienced technicians to inspect your vehicle and assess its performance, as well as diagnose any problems that may be initially hard to identify. In this way, if there are any problems with your valve stem seals, or if they’re almost due for a replacement, you can have the issue resolved promptly and accurately, without having to worry about major problems developing later on down the track.
If you’ve experienced any of the aforementioned symptoms of a valve stem seal failure, then you should ensure to bring your vehicle to European Prestige Auto Service right away. We’re the European auto mechanic that luxury vehicle owners in Perth can trust to deliver the appropriate repair and maintenance services. Apart from offering the highest level of care and commitment towards your vehicle, our team are also dedicated towards achieving absolute customer satisfaction. With a fully equipped workshop at their disposal, as well the latest diagnostic technology, our highly trained technicians are capable of resolving matters with your vehicle in a prompt and efficient manner. They’ve spent years working on models hailing from brands such as BMW, Audi, Alfa Romeo, Mercedes-Benz and more. Needless to say, you’ll know that you’re putting your vehicle in capable hands when you turn to our services.
A smooth running engine is all about timing. The modern combustion engine is made up of around 10,000 separate parts, all of which need to be in sync with each other –moving, opening or closing at just the right moment. Valves are an important part of this process, and without a functioning seal, they can’t do their job. A relatively simple part to replace, if a broken seal is left unattended for too long, vast amounts of damage can be done to the engine, potentially leading to eye-watering bills. So, the question is, how long do valve seals last, and what warning signs indicate they’re no longer doing their job.
An engine contains a lot of moving parts that require a lot of lubrication. Even so, it’s important that the oil that provides this lubrication doesn’t enter certain areas of the engine. Valve stem seals keep the oil within the crankcase and stops it from entering the combustion chamber and prevents the oil within the cylinder head becoming contaminated.
Valve seals are designed to last a long time under the right conditions, around 200,000 kilometres. Of course, you probably picked up on ‘the right conditions’ part of that sentence. Certain factors can have a significant impact on how long valve steam seals last, such as infrequent oil and filter changes, as we well as poor installation.
If a valve stem seal begins to fail, it’s important that it’s replaced as quickly as possible before profound damage is done to other parts of the engine. So, what are the signs of a bad valve seal?
Starting a cold engine is often a good way of determining the health of the valve seals. If your car has been sitting overnight or for a longer period of time, a film of oil, left over from the last time you drove, will be coating the head of the valve cover. When you start the engine, this oil will be sucked down through the failing seal into the combustion chamber, and bluish smoke will be expelled from the exhaust pipe. If you notice this, get your car checked by a trusted mechanic.
A similar phenomenon happens when idling. If you find yourself stopped for a period of time with the engine running, high vacuum levels can cause oil to build up around the valve seal. If it’s faulty, some of this oil will get sucked into the combustion chamber and bluish smoke, caused by burning oil, will be emitted from the exhaust pipe.
If your car’s exhaust continues to emit a lot of smoke throughout the journey and not just at the beginning or when idling, it’s an indication that the valve seals may be deteriorating. If the smoke comes in waves, it’s a sure fire sign that you need to get it checked.
As you can probably tell, if a valve seal is leaking oil, oil consumption must increase. One way to keep an eye on this is by using a dip stick and keeping a record of oil levels. If you find it dropping quicker than normal, the valve seals should be checked.
Engine braking is when you slow the car without the traditional means of the brakes. If you coast for a period of time, especially downhill, excess oil will collect at the top of the valve cover. When you press the accelerator, this oil can be sucked through a faulty seal, once again producing excess smoke.
Unfortunately replacing valve stem seals involves removal and dismantling of the cylinder head, which takes many hours and so labour costs are usually quite high, however recent developments by tool and equipment manufacturers have made it possible to replace these seals without the need to remove the cylinder head, slashing the time (and money) to replace them.
Faulty valve stem seals can be a minor issue – until it isn’t. They are an important layer of protection for vulnerable (and expensive) parts of the engine, so it’s important they are always functioning properly. If you pick up on any of the warning signs mentioned above, book in with our friendly team immediately before further damage can be done. To prevent issues associated with faulty valve seals, always make sure your engine’s oil levels are good and the filters are changed before they become clogged.
Valve stem seal problems are as old as overhead valves. Those puffy brown rock-hard deposits (that can look kind of like brown ice cream) on the spark plugs aren't always so noticeable on some engine platforms with leaking stem seals, but they blatantly tell the tale on others. Visible symptoms range from a puff of oil smoke from the tailpipe when starting the engine after a soak to a full blown bug-truck mist that hangs in the air for minutes after a vehicle passes. Some engines seem to give more valve stem seal trouble than others.
The intake valve stem has an intrinsic low vacuum applied because the business end of that valve is in the intake stream. That vacuum loves to draw engine oil past those little seals the engine guys designed to keep the combustion chamber clear of unwelcome lubricant intrusion from under the valve covers.
The problem is that the seals get hard and cracked, and the oil that naturally splatters around under the valve cover can make its way down past the valve and into the power-producing combustion chambers and out the tailpipe. Valve stem seals can leak badly enough that they actually push the O2 sensor readings away from stoichiometry (saw that a few years back on a 1991 Dodge pickup), and most grease and steel guys have replaced the seals on more than a few domestic V8 platforms to mitigate smoke and oil consumption.
Another side effect related to the spark plug deposits would be those peculiar little surges that go away with the EGR disabled. I got hammered by a few of those early in my career, typically on the Ford 3.8L V6 engines that still push so many Blue Oval buggies through the wind.
Conventional Wisdom vs. Engineering
On the shop floor of the dealerships and independent shops where I put in my years as a tech, we'd routinely replace valve stem seals without removing the cylinder head, and once you get the valve or rocker arm covers off, it's pretty straightforward. You remove the rocker arms and/or the camshaft (whichever is in the way, depending on engine design), then air up the cylinder you're working on with shop air pressure (you can build a hose with an old compression gauge hose) to keep the valves from dropping out of sight if the piston happens to be at something other than TDC. Then you use a valve spring compressor to squeeze the spring and magnet the keepers out of place so as to reveal the guilty seals, which can be removed.
With a neat plastic seal protector slipped over the exposed end of the valve stem (the new seals typically come with a couple of these dandies), you can install the new seals and use whatever tool you deem safe in seating them. Reinstall the springs and keepers on those valves and move on to the next cylinder in line.
Here's an important hint: Don't opt for cheap valve stem seals, or you'll be doing the job all over again. Personally, I like the ones with the garter spring – the plain rubber ones can look fine and be lousy enough to walk up the stem, in which case the vehicle will come back with a scowling owner behind the wheel.
As I investigated the matter, I recognized that the timing belt and camshafts would need to be removed to be sure. Below the camshaft and above the valve springs is a highly polished cam follower (Toyota calls this a "lifter") that rides in a machined bore and transmits the force of the rotating lobe to the valve stem. I was familiar with this arrangement, because we dealt with it when I was at the VW dealership, and the Japanese diesels in Ford Escorts and Tempos used them as well. I made a lot of money adjusting valves on Rabbits and Sciroccos.
When you remove the cam follower (older cam followers have thick shims between the follower and the camshaft for valve clearance adjustment), you can see the valve spring retainers, but the bore around the spring is so near the spring that you can't get anything in there. Since conventional on-car valve spring compressors require access to the sides of the spring, this might require some special tools and/or procedures. The Toyota dealership I called told me that they always remove the head and send it to a machine shop to have that work done.
"Poppycock," said I. Where there's a will, there's a way.
Consulting with the MAC tool man, I found that could provide me with a spring compressor to deal with this type of valve spring arrangement, but it was designed to use as an adapter to supplement a standard valve spring compressor, which does the job with the head on the bench rather than on the car. It would be a necessary purchase, but engineering would be the order of the day if I was going to make this happen the way I wanted it to.
As I regarded the original box, I discovered that the tool had been purchased from AST, a specialty tool manufacturer, (part No. TOY 165), but I haven't been able to find it in their online catalog either. It would be fairly easy to manufacture one, but you've gotta be a weirdo like me to attempt it.
Purchasing the alum spring compressor adapter (which I didn't have to build that time around), we went to work building a special spring compressor jig so as to utilize the tool we bought to remove the valve springs and replace the seals on the car. You can see the results of my work in the photo. Using a large C clamp and a steel plate with lots of holes drilled in it, we made a very useable tool that I still have in my inventory today. The ¼-inch 3x3 steel plate is only bolted onto the C clamp with one bolt and can be swiveled into a position where it can be bolted to the head, effectively providing an anchor for the "muscle" part of the compressor, which doesn't need much muscle.
The red part of the tool is gripped by a piece of an engine lift bracket that I ground to fit it, and the deep socket I welded to the modified lift bracket provides additional positioning capability as well as stability (the C clamp jackscrew just slides down into it) so as to keep the spring compressor from lateralizing during spring compression.
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China SBT Oil Seal is an international company integrating design, research and development, production and processing.
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