Ignition System Service
In the past we have covered the topic of electrical system service pretty thoroughly, and the basic premise of maintaining clean, tight connections certainly applies to the ignition system, as well. I also covered some of the basic tune-up information last month with regard to its impact on our ability to achieve proper carburetor adjustment and operation. There is so much pertinent material on the subject of engine tune-up; I do not believe we could do it justice in a single issue of ETCetera. I trust you took some time to study the Tune-Up Diagnosis chart in the March issue, if not you may want to go back and review it. The scope of tests and possible adjustments give a good indication of how an automobile’s various systems are inter-dependant, and poor operation in any one will certainly affect others adversely.
Let’s begin with spark plugs. Pontiac installed AC plugs as original equipment and according to various Pontiac parts catalogs I have, AC 45 plugs are recommended for all six and eight cylinder engines from 1934 through 1951. Beginning in 1952, the 45 plug was replaced by the AC 44-5. My research puts this plug halfway between an AC 44 and an AC 45 with regard to heat range. Based upon the plug number assigned by AC, this is an obvious conclusion.
The diagram shows the path that heat must follow away from the tip of the spark plug. Tip temperature is critical to plug life; too cool and deposits will form that can conduct away the electrical current without ever allowing a spark. If the tip gets too hot, it will actually glow with heat and ignite the incoming mixture before the spark occurs. You can see from the chart how easy it is to identify the heat range of an AC spark plug, low numbers are cool and higher numbers get progressively hotter.
AC used the letter “R” to indicate a resistor type spark plug. Resistor plugs limit the amount of electrical current flowing through the ignition system, and also function to limit interference with radio and television broadcast signals. Limiting the current flow in the ignition system is a good thing; high current flow can cause pitting of the contact points in the distributor and excessive heating of the ignition coil. Beginning in 1950, Pontiac used resistance-type spark plug wires as original equipment. These function just like resistor plugs and I also recommend using them. These plug wires feature a conductive core of graphite impregnated material and should be handled with care. It is possible to cause a break or separation by pulling or stretching the plug wire, but if handled properly they can last for years without fail.
I use AC R45 plugs in both of my cars, along with modern resistance plug wires, and have not experienced any problems with either. If you only drive your vintage Pontiac at low speeds, you should probably use a 46 heat range plug to prevent fouling. Conversely, if your Pontiac has a recently overhauled engine and you are traveling at highway speeds, the use of 44 plugs would probably allow you to run slightly more spark advance without having spark knock. The spark plug heat range you need is entirely dependant upon the condition of your engine and the type of driving you do.
If you chose to use a brand other then AC, you should follow that companies’ catalog listing for your car, do not use the cross-reference chart from the AC number! Some spark plugs have very narrow heat ranges as compared to others, if you use a different brand you should start with their recommendation, and then change to a different heat range as experience dictates.
Be sure to clean around the base of the spark plugs before removing them from the engine. Check to be sure your new plugs have the gaskets installed, they should easily thread into the cylinder head by hand. Keep your spark plug socket perfectly straight when tightening each plug, if not you could crack the porcelain insulator. A cracked insulator can be difficult to see, but will certainly result in a miss-fire condition. The recommended plug gap is .025 inch, and should be done with a round-wire type gapping tool. It is impossible to get an accurate gap with a feeler gauge or wedge-style gapping tool, especially if you are re-gapping used plugs. Spark plugs are considered to be worn out when the center and ground electrodes become very rounded from use. The sharp, straight edges of new plugs require far less voltage to “fire” then smooth, round surfaces. Used plugs can be improved by carefully filing the sides and end of the ground electrode to sharpen its corners, do not attempt to file the center electrode; when it is worn round you need to replace the spark plugs.
The distributor diagram is a good reference to show how everything fits within the housing, including the primary circuit wiring. We talked about lubricating the distributor a couple of months ago, this drawing shows the various lubrication spots rather well. Be very sparing with the grease you apply to the breaker cam and rubbing block on the contact points. You should see a felt pad in the hollow distributor shaft once the rotor has been removed, a drop or two of oil is sufficient to saturate it. A single drop of oil should suffice on each of the 3 breaker plate ball bearings around the perimeter of the housing, and another very small drop on the pivot post the contact points are mounted on. Finally, if you look just above the distributor shaft in the drawing, you will find the words “breaker plate” and just above them is a circle. This is actually a hole in the plate and underneath should be a circular piece of felt. This is another lube wick, similar to the one inside the hollow shaft; carefully wet it with a few drops of oil.
NOTE: The easiest way that I have found to do this is by using the slender plastic wand provided with aerosol cans of brake or carb cleaner. Touch the wand to the felt within the hole and allow the oil to flow down along the outside of the wand and into the hole. Be sure to wipe any excess oil from inside the distributor housing, several cotton swabs (Q-Tips) should make it easy.
The drawing further identifies the lock and adjusting screws used to set the point gap. Be sure to use an absolutely clean feeler gauge on the points, even a trace of oil is detrimental to long point life! I carefully clean my feeler gauge with “brake” or electrical contact cleaner before use, then re-oil it when I’m done to prevent it from rusting.