This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.
One of the most common systems on the 911 to require maintenance is the ignition system. Without a doubt, the cap, rotor and ignition points should be periodically replaced as they tend to wear out over time. In addition, the spark plug wires have a tendency to get old and less effective as they age. Last, but not least, new spark plugs are extremely important to a good tune up as well.
I recommend changing the plugs, rotor, cap, and points every 15,000 miles or so for 911s after 1977. For the earlier cars, it's wise to replace them a bit sooner, around 10,000 miles. With important moving mechanical/electrical parts as these, it's very important to keep them in top condition. I have seen many cars refusing to run properly because the owners hadn't replaced the cap, rotor or points in many, many miles.
The first thing to be replaced should be the spark plugs. Make sure that the car is stone cold before attempting to remove the plugs. If you try to pull them out of the aluminum heads when they are hot, then there is a high likelihood that the steel plugs could damage the threads in the aluminum heads. With the car cold, carefully pull on each rubber end of the ignition wires and remove them from each spark plug. Make sure that you don't pull on the wire itself, as this can damage it. Repeat this for all six spark plugs, and leave them hanging in the engine compartment.
Once the wires are removed, insert the spark plug remover into the access hole where the plug wires were connected. You will probably need an extension on your socket wrench in order to reach inside. Especially for the 911, I recommend the use of a swivel foot spark plug socket that can bend and twist into the tight spaces required. Make sure that the tool has a firm grip on the spark plugs, and remove them from the engine.
Spark plugs are good indicators of how your car is running. Check your spark plugs carefully, as signs of problems with the engine or fuel injection can sometimes be indicated by clues from the spark plugs. However, modern gasoline formulations sometimes can make the spark plugs black or sooty, even when the car is running properly. For an excellent description of various spark plug problems commonly found in 911s, check the Ignition System Chapter of the Haynes Porsche 911 Automotive Repair Manual, by Peter G Strasman and Peter Ward. Although brief in many sections, this manual should be in the collection of every 911 owner. It's probably the second best value in books for your 911 (the first being the book that you are reading right now!).
Installation of the new plugs is straightforward. Make sure that the small round tips on the end of the plug are firmly attached. It's also a wise idea to double-check the spark plug gap to make sure that the gap is properly set. Refer to the Technical Specification book available from Porsche or your car's owner's manual for the proper gap for your year 911 and engine.
Carefully install the plugs into the engine, making sure to stop if you encounter any significant resistance during the installation. If you use a heavy hand during the install, then you might cross-thread the spark plug holes which means that your engine will have to be taken apart for repair! Torque the spark plugs to 25-30 Nm (18-22 ft-lbs) with a torque wrench. Do not use any anti-seize compound on the spark plugs.
The replacement of the ignition wires is something that should probably be done every 60,000-90,000 miles. Although the 911 wires are known for being very rugged, the constant heating and cooling of the wires in the engine compartment can lead to hardening of the metal inside which then degrades performance. I recommend replacing the plug wires every 60,000 miles or sooner, if you are having problems with your ignition system. This figures out to be about once every five years, if you drive the car every day, and about once every ten years for occasional driving.
The replacement process for the wires is easy. Simply pull off the old wires and strap down and plug in the new ones. It is recommended that you label the distributor cap before you remove the old wires, as it can get confusing when you remove them all at once. Some of the older wires may really be attached to the cap tightly, so you may have to wiggle them slightly to negotiate their release.
I recommended that you use the stock 911 shielded plug wires on the CIS cars. These are of very high quality, and aftermarket products really only serve to change the color or appearance of the wires in your engine compartment. The stainless steel sheath on the outside of the stock wires helps to insulate and isolate the ignition signal that is running through the wire. Make sure that you attach the ground straps from the ignition wires to an appropriate plate on the engine (usually attached to one of the bolts that mounts the coil).
The cap, rotor and points are perhaps the most common items to replace on the ignition system. I recommend that you inspect and replace them every 10,000 miles or so. To replace the cap, simply undo the small straps that attach it to the distributor, and then unplug the ignition wires from the top. If you unplug all the wires from the cap at once, label the wires so that you don't mix them up when reinstalling them.
The rotor simply pulls off of the top of the distributor (underneath the cap). The new rotor can only be installed one way: there is a notch in the rotor that will make it line up with the distributor shaft. Make sure that you push the new rotor down all the way on the shaft. New rotors are also available with a built-in RPM limiter. These rotors will not let you over-rev your engine. They are available with rev-limit cut-offs at 5800, 6500, 7000, or 7300 RPM. It is important to note, however, that an RPM limiter will not protect your engine from over-revs that may be caused by a missed shift during driving.
The replacement of the points is a bit trickier, and applicable only to the 1965-76 cars. The capacitive discharge system used on the 911 should prevent the points from pitting, however, they can wear out after many cycles of opening and closing. The points are located underneath the rotor, and are screwed into the top plate of the distributor. The distributor contact breaker points together make a switch that tells the ignition system when to fire a spark. The gap should be set to an initial value, and then reset when you can check the dwell angle of the car with a meter (see Pelican Technical Article: "Setting the Timing, Dwell, and Idle Speed"). For the proper points gap value, check your owner's manual, or Porsche Technical Specifications book for your year car.
To properly set the points gap, the distributor needs to be rotated until the points are open to their maximum distance. Rotate the crankshaft of the engine (see Pelican Technical Article: Valve Adjustment) so that the lobes of the cam inside the distributor push the points open to their maximum amount. Use a feeler gauge to set this amount, and then tighten down the screw that holds the points in place. Setting this gap is only a temporary measure: you will have to set the dwell angle later on after the engine is started. After you set the points gap, make sure that you set the ignition timing for the car (Pelican Technical Article: "Setting the Timing, Dwell, and Idle Speed").
On some of the early cars, Porsche installed a distributor manufactured by Marelli. These distributors are no longer available, and at the time of writing this book, all of the supply of original caps, rotors, and points have been exhausted. There is an aftermarket company making replacement points that fit Marelli distributors. The part number is 911.602.960.00 and is manufactured by IKAR, who makes a lot of Mercedes parts. Regardless of that, the caps and rotors are nowhere to be found. Many people have called hundreds of Porsche dealers and shops around the world looking for them to no avail. The only real practical solution is to upgrade to the Bosch distributor that was also used as an adjunct to the Marelli one. This Bosch distributor is still available, and so are the basic tune up parts. The cost of the distributor is around $700 for a new one, and used ones are very difficult to find because everyone is looking for them to replace their old Marelli distributor. If you have an older 911 with one of these older distributors, you will eventually have to upgrade it to the Bosch one. The good news is that the Bosch distributor is a drop-in replacement for the Marelli and requires no modifications to the engine.
This photo shows the basic components of an ignition tune up needed for a 911SC. The plug wires are the stainless steel variety, which were installed as stock equipment. The cap and rotor are original Bosch, as well as the standard Bosch platinum plug. On the earlier cars, you will need to replace your ignition points as well. A real handy device is the swivel spark plug socket made by the Sears Craftsman line. For about $10, it's very useful for reaching into the rear recesses of the 911 engine compartment.
After pulling out the spark plug wires, use the spark plug socket to remove the plug. Make sure that your socket has the rubber insert inside of it that prevents the plug from falling out. Spark plugs can be a pain to fish out of the inside of the 911 engine.
Installing the new cap and rotor is very straightforward. About the only thing that you can mess up is the location of the ignition wires on the top of the cap. Unplug and replace each wire individually, as it is very easy to get confused and plug the wrong wire into the wrong socket.
If you happen to own an early car equipped with an original Marelli distributor, then you will probably want to upgrade to the Bosch distributor. The maintenance parts for the Marelli distributor (cap, rotor) are no longer manufactured, and are impossible to locate. The new Bosch distributor is a drop-in replacement, and replacement parts are common.