Zündkerzen sollten mindestens alle 50h gereinigt werden. Wie es geht, wird hier beschrieben:

There are a few items and procedures necessary to do a good job working with plugs, including proper removal, cleaning and reinstallation. First, of course, an appropriate socket and a good quality torque wrench for putting the suckers back in. Don't use the torque wrench for removing the plugs, use a standard socket wrench and extention. Torque wrenches are for measuring torque, not as an all-around ratchet. Also, have four old plugs painted bright orange or yellow to put in the upper plug holes to keep dirt and debris from falling into the cylinder while the plugs are out. I like to keep my tools and equipment together while I'm working and I don't care to spend several hundred dollars on standup tool cases that won't fit in the back of the old Cheeevy pickemup without taking the tonneau off so I make use of a second-hand hospital gurney. Roll it out to the plane and Doctor robert is ready to operate.

First, use a 3/8" wrench to hold the center portion--the cigarette top where the ignition wire goes into the plug--when removing the terminal hex device on top the plug-which may be either a 3/4" or 7/8" hex. Don't allow the center to rotate as you remove the terminal hex. Don't touch the cigarette section with your hands or, if you absolutely must, make certain your hands are clean. Since you're working on an engine, your hands won't be clean. Don't touch the cigarette with your hands. When you remove the plugs themselves, make sure you steady the socket and extension so you don't put sideways pressure against the body of the plug (if you're using an aviation plug socket, press down on the extension to take up the spring pressure). Make sure you drop the plugs on the concrete hangar floor. That way you have an excuse to buy new plugs and avoid all this mess with cleaning your old ones. You see, if you do drop a sparkplug, it's into the can, never take a chance on reusing the plug if it's been dropped. The ceramic insulator section is very likely to have suffered damage.

Buy or make yourself a sparkplug holder. A metal box with holes to drop the plugs in electrode up works great, you need to mark the holder so you know which cylinder the plugs came out of and top and bottom location. That's eight holes, might want to add some spaces if you ever work with six cylinder engines... Examine the plugs. If the center electrode looks like a football--actually, if it's lost 50 percent or more of its original width--replace the plug. You should get about 350 to 400 hours minimum out of a set of massive electrode plugs pulling them every 50 hours for cleaning and rotation but keep the abrasive blasting under ten seconds max for each plug or you'll eat the plugs alive.

Pick the lead balls out of the center cavity with a dental pick or, my favorite, a piece of 1/8" brass stock that I've shaped on a grinder. This is less likely to damage the inner body of the plug. Again, when the lead is out, examine the center electrode carefully. My eyes aren't that great, I use a light and an opti-visor, a device that makes up for being on earth for too many years. If there's any damage to the ceramic or the center electrode, pitch the plug.

Suffice it to say if you're not familiar with the fine art of sparkplug augury--reading plug condition--get some advice from a knowledgeable mechanic. Dry, brown tips are great. Some soot or even light oiling on a lower plug isn't exactly a sign of disaster but it's certainly a mile post on the warning road. Oil on upper sparkplugs is a sure sign that your engine is passing oil. That could be bad guides, broken rings, worn cylinder; gee, the list can go on and on. Regardless of the cause, wet oil deposits on the top plugs is a sign that the engine will need major maintenance. Lower plugs will likely have little balls of lead no matter how carefully you lean on the ground, if the entire inner body is blocked with lead, you're probably not leaning enough. If the lead deposits are bad enough, you've bought yourself a new plug regardless of the electrode condition.

Lead balls out, electrodes look good, soak the plugs in a container of either unleaded gas, varsol, naptha or Stoddard solvent, fluid should be about 2" deep. These are the four cleaners recommended by Champion for use on plugs, I'd limit my choice to one of these. That's firing end in the solvent, support the plugs so they don't fall over. Never, ever let any solvent get in the top cavity--which makes ultrasonic devices unlikely to work well without creating some sort of rack that is sure to keep the plugs from toppling over. Thirty minutes in the solvent should do it then blow the plug out with compressed air.

Now you're ready for the abrasive blaster. A "mini-shop" device costs around $25 from Chief, SanVal or other discount houses. Unfortunately, the air compressor costs somewhat more. If you're gonna have a fairly complete shop, an air compressor is one of those investments you might consider. There are many uses for compressed air, including application of solvent, operating various tools and inflating tires. OK, back to the cleaner. Ten seconds or less of abrasive, several more seconds with the switch turned to "air" to clean the abrasive bits out of the inner plug body and after you've removed the plug from the cleaning device, blow it out again with a hand nozzle on that new compressor your significant other will be angry you bought. Check the plug threads, I prefer using a small hand wire brush if there's any sediment buildup on the threads. If the threads are really damaged, chuck the plug in the trash or paint it yellow and use it to as mentioned above. Even then, you might want to chase the plug threads so they don't cause head damage.

Now, use the gap adjusting tool and gap wire. I keep one of the little hand adjustment tools--costs about ten or twelve bucks--in the tool kit in the plane. Champion makes both a bench mount and a "hand held" unit for the shop, if you check with auto repair places you may be able to find an equivalent of the aviation unit for about two thirds the cost, around fifty bucks or so. The automotive tool number is CT 415 B. Again, I don't mind using the ten buck hand gadget but a nice bench adjuster is really convenient. Just remember, when you're gapping the plugs with the "go-no go" wires, don't put too much pressure on the outer electrode. If you close the gap too much, you've shot the plug. Idea is to pass the .015 straight wire through between the center and outer electrode but the .019 won't go. Also, turbo-charged engines like slightly smaller gaps, particularly at altitude. That, of course, means it's OK to gap them closer to .015...it's so damned hard to get in and make changes while you're flying. Don't force the gap wire, don't put pressure on the center electrode, never use the electrode adjuster with the gapping wire in place between the electrodes...

Most of us don't have a "bomb testing" unit at our bench, it's nice to test the plugs at least every 100 to 150 hours when they're cleaned. If they fire under the 2,000 pounds of pressure in the tester, they'll most likely fire in the cylinder. Ask your friendly local shop what they'll charge to bomb test the plugs or have your A&P do it at annual time. Hopefully he already does this test but it never hurts to verify.

Reinstallation. If you're comfortable with the job, chase the plug threads in the head with a thread chaser, Champion makes one that's designed to pick up debris and keep it from falling into the cylinder. If you don't know how to tell whether a helicoil insert might have been used, settle for wiping a toothbrush lightly coated with general purpose grease in the plug hole, that will help prepare the head for plug reinsertion. Using a chaser on an helicoil insert can destroy the insert, that translates as money to fix, often much money.

Cigarettes, the little center plugwire insert, should be cleaned with a cloth dipped in MEK (or, if you're concerned with damaging the silicone above the spring, use denatured alcohol) after examining the spring and tip for cleanliness. If there's any sign of corrosion on the metal, scrape the tip inside the cigarette until it's shiny. DON'T touch it with your fingers, use a cloth to hold the unit. Body fluids are corrosive, just ask President Clinton.

OK, we kept the plugs in the order in which they were removed. Now it's time to rotate the plugs. They go back in with top to bottom rotation moving up one number in firing sequence. Firing sequence for a 360 Lycoming is 1-3-2-4, that's for all series except the LIO suffix which fires 1-4-3-2. Sixes are usually 1-4-5-2-3-6 for Lycoming engines. Check your book for Contenental. This rotation is important, it compensates for plug wear caused by constant polarity discharge. Each lead from a given magneto fires in opposite polarity from the lead before and after it, causing variations in electrode wear that can be evened out with this rotation. We will have new copper gaskets on each plug, they're all of eight cents each--unless you enjoy annealing your old copper gaskets.

Use a few drops--like as in two or three--of Champion anti-seize on a tiny brush to prepare the sparkplug threads or buy the silver Permatex paste that's less likely to run down the threads on the upper plugs when you're installing them. Do not, repeat, do not get the antiseize on the plug electrodes. It will cause permanent problems. Too little is far better than too much. This anti-seize, applied properly, will help eliminate problems removing the sparkplugs next time they come out. It's also great for the many inspection plate screws in the Mooney.

Turn the plugs in by hand before using the wrench. We aren't nearly as likely to cross thread the plugs when they're inserted by hand. Lyc book says 35 foot pounds (420 inch pounds to be precise), Continental says 25-30 pounds, 30/32 should be plenty. That's 30 pounds when the torque wrench clicks, not after the third or fourth click...

Insert the cigarette units, tighten the terminal hex finger tight then give it a bit more tension using a wrench. It's a big nut but doesn't require much torque, don't overuse that big wrench.

Before buttoning up the cowling, this is also a good time to spent half an hour with an inspection mirror and a light. Check for oil leaks. The Lycoming is easy to keep from leaking. If your engine is clean, it's much more simple to determine if there's a crack somewhere or a loose fitting. Unfortunately, air pressure under the cowling can force oil to track everywhere in the compartment. In extreme cases, using a flourescent chemical in the oil is almost the only way to find the source of a leak. These are jobs for a competetent A&P mechanic but discovering that your aircraft has a problem is the first step in the process. Sure, there's a knot in the bottom of your stomach when you realize that you have some work perforrmed but it's much better to discover damage on the ground than in the air.

Freshly cleaned and gapped plugs in place, cigarette connectors cleaned and wire harness inspected to ensure there's no damage, you should now have less of an rpm drop when doing your mag check than you did before cleaning the plugs; important is that one mag to the other is not more then 50 rpm in total drop. Repeating this cleaning and procedure every 50 hours will provide a meaningful way to monitor engine condition, will improve overall performance and save maintenance money. It's a legal FAR Part 43 maintenance procedure for owner/operators to perform on aircraft operating under Part 91. Each time, make an engine log entry specifying what you've done, the results and the return to service with your name and certificate number.

I keep two sets of plugs, both identified with total time in service and which cylinder the plugs came out of when I pulled 'em. That way I can take out the 50 hour set, insert the cleaned ones into chased plug holes and button the engine up in a couple hours total including cleaning the engine and inspecting. I later renovate the plugs that came out at my leisure and avoid skipping steps because I'm in a rush to get the bird back in service.