Spark Plug Replacement

APPLICATION: This procedure will generally apply to all air-cooled Volkswagens.

The spark plugs generally should be replaced every 30,000 miles. Some plugs, like the platinum spark plugs, can go longer than this. However, if the plugs become fouled or wear out before 30,000 miles, they must then be replaced sooner. Replacing the spark plugs is a fairly simple operation. It requires a special spark plug socket, and a ratchet with a few long extensions. It also requires some type of anti-seize product.

The spark plugs on an air-cooled Volkswagen engine are threaded directly into the aluminum cylinder head. Due to the different expansion rates of the spark plug metal and the cylinder head metal, the spark plugs should only be removed when the engine is cold, if possible. This reduces the chances for stripping or galling of the threads in the cylinder head.

The first step is removing the old spark plugs. To do this, you must first remove the spark plug wires from the spark plugs. A good tip here is to only remove one spark plug wire at a time. That way, there is no chance of possibly getting the spark plug wires mixed up. So, for orderliness, start with the spark plug for cylinder number 1. Number 1 is the front right cylinder on an air-cooled Volkswagen. There is a number stamped into the tin next to each spark plug, so observe where you are.

First remove the spark plug wire. Twist it as you pull it off. Always pull by the plastic connector, never by the wire itself. If you pull by the wire, it is likely to pull out of the plastic connector. Once you have the wire off, look down through the tin to see your spark plug staring at you. If it is a Type 1 engine you will probably only be able to see the very tip peeking out from under the tin. If you have a late Bus, you will find it easier to do this work from the open interior hatch in the luggage area. If you have a Vanagon, rejoice, this is super-easy to get to. Try to fit your spark plug socket (attached to ratchet, of course) on the spark plug. You will have to experiment with various extensions to get it on. If you find that certain engine bits are in your way (air cleaner, etc.) go ahead and remove them.

Once you've got the spark plug socket on, set your ratchet to "loosen" -- make sure, now -- and then unscrew the spark plug. It may be hard to loosen, especially if you have a long extension, but hold the extension straight and carefully loosen it. When it breaks free, unscrew it slowly, feeling for any binding. If it loosens and starts coming out but then seems to be tightening, stop. Tighten the plug up a bit and then loosen a bit. Repeat as necessary, you don't want to damage the threads, but it may not be avoidable. You can try spraying a little penetrating oil on the threads if you're that limber, but just be careful. If the plug comes out OK, be happy. If it comes out with little metal spiral shavings clinging to it, you've got a problem.

Check out the old plug. The color should be a nice even tan to gray color. It should not be physically damaged, nor should it be wet with oil or have black fluffy carbon deposits on it. Physical damage indicates that something solid got into the combustion chamber and banged around for a while. Oil fouling indicates that a lot of oil is getting into the combustion chamber. May be time for new rings or valve guides. Excessive black fluffy carbon deposits indicate a rich fuel/air mixture. This is just a basic guide of the most common things you will find. The Haynes manuals have a nice full color photo chart of various spark plug colorings and their causes. Reference this chart.

Now remove the old spark plug from your socket while thinking about what you need to do to your engine (adjust mixture, etc.). Place the new spark plug in the socket. Decide whether or not you need that little metal screw-on terminal. Did the one that came out have it? If not, you don't need it -- unscrew it. If so, keep it on there. Your spark plug wire will only fit one way. Now you need to gap the spark plug. I believe the gap should be .026", but check the manual to be sure. You check the gap between the electrode and the insulator with an appropriate feeler gauge. Bend the electrode as necessary to achieve the proper gap.

Now coat the threads of your plug with some anti-seize compound. Then remove the ratchet from your extension and hold the extension by hand. Start threading the plug into its hole this way. If your old plug came out with some metal shavings, be VERY VERY CAREFUL about how you do this. You do not want to cross-thread the new plug. However, if the old one came out with shavings, it is likely that someone else has cross-threaded the plug in the past. I personally have never had this problem but I believe the solution involves removing the cylinder head and having a thread insert installed.

This is why you want to start the plug by hand. It should start easily and turn easily as you thread it in. It should not immediately bind up in its hole. If it does, take it out and start over again as you were likely cross-threading it.

Once you get the plug hand-tight, then tighten it down with the ratchet. The torque spec is usually only around 20 ft-lbs (reference your manual), so don't overdo it.

Now replace the spark plug wire. It simply pushes onto the new plug. Then repeat this procedure for the other three spark plugs.

NOTE: Those of you with Type 4 engines will find replacing spark plugs numbers 2 and 4 quite fun. They are deep beneath the tin and are at a weird angle, so a long extension is a must, as well as a good memory, so starting the plug in its hole is easy. You may drop one of those plugs out of your socket and down onto the cylinder head, out of reach. If so, get out your handy telescoping magnet on a stick (I'm serious, you should have one of these anyway) and fish it out. If you can't get it, just leave it in there with all the other spark plugs dropped by POs. But really try to get it out as I imagine having that spark plug laying there hampers cooling somewhat.

You may also want to take this opportunity to replace your spark plug wires. Tell-tale signs of bad wires are corrosion on the terminals, stiffness of the wires (they should be soft and pliable), rough running in moist humid weather, etc. Replace your plug wires with Bosch wires. These cars run best with Bosch ignition system components. Trust me on this one. The Bosch wires usually run around $20 for the whole set, and they come with the necessary spark plug wire air seals, which seal the hole in the tin so that vital cooling air does not leak out, compromising engine cooling.

Replacing spark plug wires is very straightforward. The set will usually come with 6 wires, four for the regular spark plugs and two wires of different lengths for the lead from the ignition coil to the distributor cap center terminal.

Follow the instructions in the package for replacement. Again, do only one at a time so that there is no mix-up. You will find that the four spark plug wires are all of different lengths. Obviously the spark plug farthest from the distributor cap gets the longest one, and the closest plug gets the shorter one. Use the wire of appropriate length for the connection between the coil and distributor cap. Save the other wire and the two longest good old plug wires for your box of spares.

Make sure that all spark plug wire ends are firmly seated on their connections both at the distributor cap and spark plug ends, and also do the same for the wire from the coil to the distributor cap. Fit the wires into the existing plastic clips in various places on the engine for this purpose. This keeps them from draping against hot surfaces or wearing out by rubbing through.

Once you have done all this, you are finished. Start the car to make sure it runs fine. If it doesn't start or runs rough, re-check all your connections -- make sure you didn't get any plug wires mixed up. The firing order for all air-cooled Volkswagen engines is 1-4-3-2, so make sure the plug wires go around the distributor cap clockwise in that order.

If your old plugs were worn out or if your wires were dodgy, you will likely notice a great improvement in how your engine runs.

Sean Bartnik
February 8, 1998