It is no secret that if you want your Volkswagen's motor to last more than five or ten thousand miles between overhauls, you have to change the oil and adjust the valves. Changing the oil is easy, provided you have someplace to dispose of the waste oil (Hint: Don't pour it down a drain or dump it out on the ground. Find a garage or service station that recycles its oil and leave it with them.
Adjusting the valves is a little more work, but it is no less important. As your motor runs, the heat and the force of the valve spring pulling the valve closed can stretch the valve stem, making the valve longer. After enough stretching, the small amount of clearance between the adjustment screw in the rocker arm and the end of the valve will disappear. When this happens, the adjustment screw will begin to hold the valve open a little instead of letting it close fully, not allowing a good seal between the valve and the valve seat, so you lose power. Even if that were the only result of having tight valves, it would be bad enough. Unfortunately, there is another reason why the valve face must seat firmly against the valve seat.
Inside the combustion chamber, there is a lot of heat created by the burning gasoline. Some of this heat soaks into the head of the valve. The valve has only three ways to disperse this heat: cooling due to the intake charge, heat dissipation through the valve stem and heat dissipation through the valve seat.
Racers and other high-performance enthusiasts can use what is called "charge cooling"to help keep the valves alive, but unless you are an expert at this sort of thing, you can pretty much write off charge cooling as the answer to your hopes for a cool running engine.
That leaves heat dissipation through the valve stem and seat. Valve stem heat dissipation is pretty much a function of the valve stem diameter and the condition of the valve guide. This is on the reasons why it is so important to have good, right valve guides.
With the scrawny, little valve stem you find on a Volkswagen valve, however, it is clear that a lot of the cooling has to come from planting the valve face on the valve seat long enough and firmly enough to allow heat to transfer from the valve head to the cylinder head.
Now that you understand all of that, it's time to start thinking about adjusting your valves. You are going to need some valve cover gaskets, a 13mm wrench, a screwdriver and a feeler gauge. Check your owner's manual (or a Bentley manual) to find out what thickness feeler gauge you should be using. If you have neither of these sources, get a 0.006-inch feeler gauge to start out with stock engines (some experts recommend setting valves at 0.004 inch, but to start with 0.006 is fine--it gives you some margin of error until you get good at this.) It helps if you are able to get your car up in the air a little with a set of jackstands or a hoist. Open the engine cover and manually turn the motor until it is at Top Dead Center (TDC). IT doesn't matter whether piston one or piston three is on the compression stroke, just find TDC.
Now, slide under the car and pull off the valve covers. If your hands aren't strong enough to do the trick, wrap a shop rag around the valve cover bail, grab the two ends of the rag and pull outward and downward sharply. The bail should snap off. Depending upon how long the valve cover has been on (and how hot the car has been), you might have to pry the valve cover away from the head with a screwdriver. Place the valve covers on the ground so that they catch any dripping oil.
It should be pointed out that Volkswagen valves are adjusted with the engine cold. You can't drive home from work, pop the covers and do a "quickie"adjust, then speed off for the evening. The motor must sit long enough so that it is cool to the touch. It might not be very convenient, but at least you won't be burning your hands on this job.
As you look up into the engine, you can see there are four valves on each side of the engine...eight in all. Reach up and manually check for clearance of the four closest to you. You should find that there are two "patterns"to which valves have clearances and which valves don't. Either the front three valves will have clearance (and the back valve will be tight) or the back valve will have clearance (and the front three will be tight). I say "should" because if you have a valve that has lost all of its clearance, it won't be loose under any condition, but that's the situation we're trying to prevent, right?
Insert your feeler gauge between the end of the valve stem and the end of the valve adjustment screw. If you have never done this before, give yourself some time to get used to the way the feeler gauge feels. The gauge has to be held "just right" in the gap. If you twist or pull on the feeler gauge you will get an erroneous feel for what the gap is.
You are looking for the feeler gauge to slip between the valve stem and the valve adjustment screw with a little resistance. If the feeler gauge falls out when you release it, the gap is too large. If you have to force the gauge in and then strong-arm it out, the gap is too small.
Let's assume that by this point you have determined that the gap isn't right. Take the 13mm wrench and loosen the jam nut on the valve adjustment bolt for the improperly gapped valve. Use the screwdriver to change the gap while you monitor your progress with the feeler gauge. If you want to get really trick, many retailers offer a combination wrench and screwdriver just for adjusting your valves. Be careful that you don't clamp down on the blade of the feeler gauge while you are tightening up the adjustment because you will deform the gauge material and it will be more difficult to get a good feel for the gap.
When the gap feels right, hold the adjustment screw with the screwdriver and use the 13mm wrench to tighten up the jam nut.
Murphy's Law states that if the gap feels perfect, the adjustment screw will try to turn when you tighten the jam nut. That's what the screwdriver is there for. It might take a couple of tries, but don't panic. Make certain to double check the clearance after you tighten down the jam nut.
Repeat this procedure with the other three valves. You are now half done. Go up topside again and rotate the engine 360 degrees until the TDC mark comes up. Scrunch under the car again and check the clearance pattern. You will see that it has reversed itself from side to side. The three that had no clearance on one side now have clearance and the one valve with no clearance on the other side now has clearance as well. You can now adjust the remaining four valves as you adjusted the first four.
It all sounds pretty rosy in print, but there are things that can come up. If the rocker arm isn't bolted down tight, your adjustments will be off. There is a far more common problem, however, and it can be pretty aggravating. You insert the feeler gauge into the gap and notice that there is too much clearance. You turn the adjustment screw a small fraction of a turn and suddenly there is no clearance. And no matter how long you fool with it there isn't any middle ground; the adjustment is either too loose or too tight.
Here's what's happening: The ends of the adjustment screws have developed little flat spots from misadjustments, oil breakdown or just plain age. The cure is to pick up a new set of adjusters. They normally come with jam nuts, which is good because they can get pretty rounded off. Replace the old adjusters with the new adjusters and life should once again be a bowl of cherries for you.
Clean out the valve covers and replace the old valve cover gaskets with the new gaskets you bought. You do not need glue to keep the gaskets in place. Put the covers back on and snap the bail wires in place. Let the car off of the stands and check your oil lever.
By checking your valve adjustment every 2,500 to 3,000 miles when you change your oil, you will help ensure that you will never fall prey to a burnt valve.
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In this photo of the driver's side of the car, the engine is at TDC for cylinder three. The front three valves (on the left with the arrows under them) are all loose and ready to be adjusted. |
In the photo of the passenger's side of the car, the engine is still at TDC for cylinder three. The rear valve (on the left, with the arrow under it) is loose and ready to be adjusted. |
Halfway done. Turn the crankshaft 360 degrees and you will again be at TDC with the distributor rotor pointing the other way (toward the number one plug wire). When the motor is at TDC for cylinder one, the right three valves on the right side of the engine (see arrows) will be ready to adjust. |
At TDC for cylinder one, the single rightmost valve on the left side of the engine (see the arrows) will be ready to adjust. |