Aviation From My Rocking Chair: You Light Up My Life or Keeping the Spark Alive

Hello again, my friends. This month I decided to write about changing spark plugs. Now before your eyes glass over, I think you will find this information interesting and the kicker (at the end of course!) may save you up to 50% in spark plug cost for a flat-opposed engine with dual ignition. First, the reminders:

(1) Use only spark plugs recommended by the manufacturer. Incorrect plugs can effect plug life and engine performance.

(2) After loosening plug leads, pull them straight out of the plug barrels. A side load can damage the barrel insulator or the ceramic lead terminal. If the lead is stuck in the plug, turn it slightly left or right. That should pop it loose.

(3) Remove plug by holding your socket in alignment with one hand and applying steady pressure to the ratchet handle with your other hand. If the plug will not come out, DO NOT USE A CHEATER BAR!! You must put all the plugs back in and run the engine until cylinder head temperatures come up to normal range. The plug should now come out. From experience, it is much easier to do this before you start the plug change, but BEWARE; those plugs are going to be very HOT. Wear gloves.

(4) As they are removed, put the plugs in a tray (Champion makes one or you can drill a wooden block to fit) arranged by cylinder number, and position either top or bottom, with the electrodes up. (5) Now, you get to be the inspector. Here’s what a spark plug can tell you: a) Normal plug- Will be brownish/gray with some slight electrode wear.

b) Carbon fouled - Dry/fluffy black deposits caused by rich fuel/air mix at idle or cruise, excessive ground idle, poor carb adjustment, or plugs with too cold a heat range.

c) Oil fouled - Black, wet deposits on bottom plugs. If oily deposit is found on top plugs, suspect damaged piston, broken or worn piston rings, sticking valves, worn valve guides, or faulty ignition. On new engines, the rings may not yet be seated.

d) Lead fouled - Light tan or brown on firing end of plug. Severe fouling shows as a dark glaze, discolored plug tip, or fused globules.

(6) Clean the plugs with an approved solvent and then blow dry with oil-free shop air. A spark plug sand-blaster can then be used to remove minor deposits. Be sure to keep plugs in the rack by same cylinder and position as removed from the engine.

(7) After cleaning, check electrode wear. If within serviceable limits, set the plug gap to the minimum recommended number. For instance, if the range is .016-.021, set the electrode gap to .016 which will allow the gap to wear to .021 and still be in tolerance.

(8) Rotate the plugs. I have always swapped plugs from top to bottom in the same cylinder and this still works. There is however, a new way (to me) to rotate which may increase plug life by 50%. O.K. y’all have waited long enough. Here is the procedure (if I can explain it well enough!) A spark plugs firing polarity causes wear either to the ground electrode or the center electrode. A magneto uses a rotating magnet to generate electricity, the north or south poles of which send Positive voltage down one lead, and Negative voltage down the next lead. To equalize wear, let’s move the plugs to opposite polarities. But, that’s not all; plugs can wear unevenly from lead salt deposits in Avgas. Moving plugs from top to bottom will tend to equalize this wear. And finally, the longer the lead-the greater the capacitance-the greater the electrode wear. Swapping long and short leads tends to equalize this wear.

So, Rick, What does all this mean? It means, dear friends, that there is a way to ensure that center and ground plug electrodes wear at approximately the same rate and should result in much increased plug life. If I can have your attention, here’s how:

4 cylinder (T=Top and B= Bottom). Looking down at your tray with #1 cylinder on your left, swap #1T with #4B, #2B with #3T, #1B with 4T, and 2T with 3B.

6 cylinder. Swap #1T with #6B, #2B with #5T, #3T with #4B, #1B with #6T, #2T with #5B, and #3B with#4T. Rotate your plugs like this every time and it should more than pay for your EAA membership. (9) Time to reinstall these hummers. Apply a thin coat of anti-seize compound to the plug threads being sure to keep it away from the bottom 2 threads. Put on a New gasket washer. These are cheap blow out insurance and should always be new. Check the plugs one more time and install them. Torque the plugs to manufacturer specs. Clean the plug lead terminal sleeve and plug shielding barrel with a lint free cloth and solvent and then install the plug lead. Finally, torque the coupling nut while holding the lead elbow to prevent twisting. O.K, Troopers, thanks for hanging around the old rocking chair and from my family to yours… Have a Happy Christmas and a Wonderful New Year.

Rick Vaux TC 4130