SPORTPLANE BUILDER

Tony Bingelis

THOSE AMAZING SPARK PLUGS I guess everybody knows what spark plugs are and what they do ... in a vague sort of way, that is. Anyhow, most of us know enough about spark plugs to have gotten by so far. But, could it be that some of us are unaware of essential spark plug information that could well affect our pocketbook and perhaps the safety of our future flights? Here's a brief review of the essentials, and what we should remember about spark plugs especially the parts they play in the safe operation of our engines. Spark plugs don't look very impressive, but be assured that those simple looking steel plugs screwed into your engine are precision-built and sturdily constructed to withstand extreme temperatures and pressures during engine operation. They are far more complex than their outward appearance would lead you to believe. It is not surprising, then, that spark plugs are expensive little buggers and, if for no other reason, deserve careful handling and a certain amount of attention. After all, by the time you pay for the eight shielded spark plugs your little fourbanger Lycoming or Continental needs, you will have parted with about $100.

used spark plugs to determine what kind of story they can reveal about themselves and the part they played in the engine's operation to date,

If Spark Plugs Could Talk You might overhear some pretty candid remarks: About being lead fouled: "My appearance due to those cinder-like deposits or dark glaze you see was caused by the engine operating too cold. Sometimes the fuel doesn't get

vaporized like it should and, of course, the high lead content of the fuel I'm exposed to is mostly to blame a good part of the time." About being oil fouled: "On the other hand, you can bet my wet, oily appearance with carbon deposits is usually brought on by piston rings that are broken or worn. Sometimes, however, it is due to excessive valve guide clearance. And, naturally, during an engine's break-in period I can get oil fouled also . . . hopefully though, the fouling will quit when

Are Those Plugs Right For Your Engine?

Pull the terminal sleeve assembly straight out taking care not to damage the spring, cigarette, or barrel insulator.

Spark plugs come in two sizes, the smaller ones fit the 5/8" x 24 threaded cylinder holes while the larger cylinder spark plug openings take the 3/4" x 20 plugs. Your engine probably came into your possession with the spark plugs already installed. If the engine was new you would naturally expect that the engine manufacturer had installed the correct plugs. However, if you bought a used engine, it is quite possible that the previous owner may not have been using the right spark plugs for the engine. Verify for yourself that the plugs installed are the correct ones as shown in the FAA and manufacturer's approved spark plug listing. This is extremely important because if, for example, the wrong reach plugs are installed, spark plug seizure and improper combustion may occur. Not only that, you should inspect those

Be sure to seat the spark plug wrench securely on the plug hex. Use both hands to loosen the spark plug. Be careful not to cock the wrench lest you damage the plug.

68 MAY 1995

the rings seat themselves." About carbon fouling: "Most often I acquire that black, dull, sooty

DRILL HOLES WITH 7/8" "UNIBIT" (STEP DRILL)

deposit because of an idle mixture that is too rich. Often the condition is brought on, or further aggravated, by excessive ground idling . . . and you know who is guilty of that." About being worn out: "We spark

plugs get old and worn out, too, you know. That's when my ground and center electrodes become eroded leaving my electrode about half its original thickness. This may be normal with the passage of time but, on the other hand, it indicates I am eligible for retirement." About being normal: "When I am myself you know I am the right plug for the engine's heat range requirements and my appearance is a nice healthy brownish-gray with only a slight sign of electrode wear. All I need is a little bit of cleaning and, maybe, regapping before you put me back to work. Oh, yes, how about giving me a nice new engine seat gasket, too?" You can bet your boots spark plugs could tell you plenty more about their trials and tribulations and how they

SPARK PLUG (FIRING END UP)

ALUMINUM .050" - .063 BEND LINE

would like to be treated, but let me

take it from here.

How To Remove Spark Plugs This is a relatively easy job providing you follow the proper procedures for removing the spark plugs: 1. First, loosen the shielded termi'BEND 75' nal elbow nut on the top of the spark plug. Use a 3/4" open end wrench (most small Lycomings). These igniHANDY ONE-PIECE SPARK PLUG TRAY Electronics® International 5289 N.E. Elam Yng. Pkwy. #G200, HillsboroOR97124 (503)640-9797

you have thoroughly checked both ignition systems. Start the engine and make your mag check only after the engine has warmed up a bit and the rpin has stabilized. Naturally, you would expect a rpm drop when switching to a single magneto operation. However, pay particular attention to the amount and speed, or absence, of rpm drop: 1. A fast rpm drop almost always means the spark plugs or ignition harness is faulty. This, naturally, has an immediate effect on the power output for the cylinder(s) affected. 2. A slow rpm drop is often the result of incorrect ignition timing. Late timing is indicated when the charge is firing too late in the piston's travel. Therefore, the power loss is higher than normal for single ignition. This power loss is rather slow as compared to the instantaneous drop accompanying a dead spark plug. 3. Sometimes on an ignition check an incorrect fuel mixture may also show up as a slow rpm drop when one or more spark plugs are affected.

A Few Practical Suggestions Buy a second set of spark plugs before you need them. Be sure they are the recommended plug for your engine. Both Champion and Auburn have

application and service manuals listing

FAA approved plugs for a variety of engine. Or you can check with your nearest aviation parts department for the best spark plug for your engine. You should pull your plugs and look at them at least once every 100 hours. Of

If you wish to contact the author of this column for additional information, please send a SASE to: Tony Bingelis

8509 Greenflint Ln. Austin, TX 78759 BOOKS BY TONY

The following books by Tony Bingelis are available from the EAA Aviation Foundation, EAA Aviation Center, Box 3086, Oshkosh, Wl 54903-3086, 1800-843-3612. Major credit cards accepted. -Sportplane Builders (Aircraft Construction Methods, 320 pages) #21-30140-$19.95 -Firewall Forward (Engine Installation Methods, 304 pages) #21-13950-$19.95. -Sportplane Construction Techniques (A Builder's Handbook, 350 pages) #21-01395-$20.95. Add $5 (1 book) postage and handling, $8 (2 books)... or order all three (#21-13954) for $52.97 plus $9.50 postage and handling. Wisconsin residents add 5% sales tax.