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Oil & Filter Change Tips

Several critical steps are needed to do an oil change properly in an aircraft engine

by Kim Santerre

Many aircraft owners have changed their own car's oil and filter many times without any problems. Besides forgetting to put the drain plug back, how much can go wrong? Well, just go talk to a few mechanics about the potential horrors of owner-performed maintenance.

Many have stories to tell that will curl your hair. Well-meaning people can do really damaging things, and they usually do it because they just don't have a proper frame of reference for proper procedure.

Over time, we've collected a number of mistakes, some of which are committed by pros-not from lack of knowledge, but more likely by a lack of time, since most owners will never know the difference if certain steps are skipped. One more reason to do your own oil changes.

You should also take a sample of the oil while it drains right out of the drain hose, not the bucket. Take the sample after a quart of two has already drained for best accuracy.

Perhaps one of the more common mistakes comes in handling the old filter. I've seen mechanics of all stripes, from well-meaning owners to experienced IAs, remove the old filter and promptly pour its contents into the bucket of old oil. "What could it matter?" is the usual response when you point this mistake out.

Plenty, if you start finding anything inside the filter. Which brings us to the next common mistake of skipping the oil filter postmortem. Sure, it's a messy job. But, if you value your engine at all, you should be doing it.

(See the setup on page 10 with a dedicated bucket and a lid, and funnel that is kept clean between uses. It makes the oil/filter change process faster, easier, and much less likely to introduce contaminants into the oil while handling or checking.)

Any mechanic worth his salt will do it as a matter of routine, although we've seen more than one shop where doing this procedure is questionable. We've even heard of shops charging for doing a filter inspection that was only serving as a source of extra revenue, and nothing was really being done.

Whether you do it yourself or get it done, have that filter cut open and the element examined. Ask to see the results-even have them save the metal filter housing (you marked previously to make sure it's your filter), media element, and if any debris in a separate, plastic bag.

Any abnormal findings should be further analyzed to determine exactly what it is, as there are a number of possibilities. With the exception of a new engine, finding anything is cause for further analysis.

A new engine can be expected to make some metal initially, and a trusted mechanic can help you decide how much is acceptable. As a general rule of thumb from the manufacturers a quarter teaspoon and nothing bigger than the graphite tip of a pencil is the upper limit without immediate need for determining cause.

You will want to maintain any findings for the life of the engine with the care of an archaeologist, or at least a plastic bag stored where you can find it. What is found in one examination may bear heavily on the next inspection. Don't count on oil analysis to find these things.

The Cutter
Cutting the filter is another area ripe for mistakes. If you don't use a real filter can cutter, you are asking for trouble. Besides risking harming yourself with some jury rig, you will waste time and probably contaminate the element with paint chips or metal shards from the can.

The venerable Champion can cutter has been around for years, and thanks to people harping on the expense of the Champion, there are a number of much less expensive models available. Aircraft Spruce has several models (ph 800-824-1930).

Used properly, these things work great. One common mistake with the Champion and similar cutters is not applying enough pressure in the first cutting round. Because of the cutter's design, if you don't cut completely through by the second or third round, you wind up cutting a spiral and the filter top doesn't come off cleanly.

Screw the knob down until the cutting wheel pinks the filter can, then twist away one turn. Then screw the wheel in another turn and rotate the filter again. It should only take a few turns.

The Inspection
Another common mistake comes in inspecting the element. Don't be content to simply spread the pleats and have a look. Cut this puppy open. Most filter elements have a metal closer that holds the ends of the pleats together.

A pair of diagonals will make short work of this. Then cut the pleats away from the metal holder with a serrated knife. An old steak knife will work OK and an old bread knife will work perfectly.

Saw through both ends like stale French bread. Don't get too carried away and grind into the inner metal wall of the filter. Spread the pleats out on the clean work surface you prepared with clean cardboard or newspapers.

Take a clean magnet and run down each groove. If not each groove, then run your magnet along the pleats the long way with the element spread out. The pleats cover several feet if stretched out, but you can make do with three feet of room or so.

If the magnet comes out fuzzy, you may have a problem brewing (in fact, probably have a problem brewing). And if you see anything suspicious, take the element and rinse it in a clean pan of solvent.

Be careful where you use the solvent (a well-ventilated area is important) since the fumes are not particularly healthy. Drain this mixture through a clean shop rag (a coffee filter is even better) and see what comes up.

Do the same with the oil that's left in the filter can (that's why you should save the oil in the filter can and not pour it out immediately-it gives you a little more engine oil to check). Let the filter drain thoroughly for less messy opening later.

Fortunately, finding anything of consequence is relatively rare-and that should make you very happy. Just because you sprung for the cutter don't hope to see something ugly. There are options for a pro to investigate your findings. See the later section on Second OilPinion.

With respect to oil analysis labs, our current recommended oil analysis lab is Blackstone Labs, Ph 260-744-2380, www.blackstone-labs.com. Whichever lab that you select, be sure that they cater to aviation oil.

New Filter Installation
Having gone through all this and found nothing amiss, you're ready to install your new filter. (Note: On some installations, most notably some Continental-520 installations, fooling around too long between removing the old filter and installing the new one can mean losing prime in the oil system, which shows up as no oil pressure on start up.

To avoid this potential problem, put you new filter on without wasting too much time. But before you mindlessly screw that thing on, take a moment to examine the filter's base and gasket. Is it clean? Intact? Warped?

Is the new gasket on the new filter secure? It's best to find problems like this now, when you can just grab another filter, rather than wait until everything is back on the engine and it's a real pain to fix.

Turn the filter over and give it a few raps to see if any thing is in there that shouldn't be. You'd be surprised at the number of times little hunks of cardboard, tufts of lint and so forth come out of a brand-new filter.

Take a few moments to examine the filter adapter on the engine, too. Is it clean? Warped? Cracked? Dented? Is there an ancient filter gasket still clinging to it? Is the filter still within the use by date?

Make sure you lubricate the gasket. Most spin-on filters specify Dow-Corning DC-4 lubricant (indeed, you may well see a message printed right on the side of the filter itself instructing you to lubricate the gasket with DC-4).

Squeeze out a dab of DC-4 onto your finger or right onto the gasket, then smear it all the way around. (For cartridge-type filters, lubricate the gasket with clean engine oil-do not use DC-4 on these.)

If your filter installation allows, you may want to carefully fill the filter with new oil before spinning it on. This will help eliminate the air bubble that would otherwise have to circulate through the system.

It's not considered as big a deal with aircraft engines as it is with auto engines, where designers sometimes go to great lengths to make sure the filter installs upright for exactly this reason. But if you can fill the filter first, go ahead and do it.

Don't overtighten the filter. The manufacturers are quite specific about how tight they want that filter, with most calling for 18 to 20 foot-pounds of torque. If you don't have a torque wrench or can't get a wrench onto the filter, tighten the number of turns as specified on the can after the gasket contacts the adapter pad.

Champion-style filters make life easy in this regard, providing a handy 1-inch wrench "nut" on the end of the filter can. Other filter brands offer you the challenges of using a strap wrench.

You can beat the rap here, so to speak, by investing in a Lyle filter wrench appropriate for your installation. Lyle makes cap wrenches that fit 3/8" ratchets (and hence a ft-lb torque wrench), and they also make a band-style wrench (albeit in 1/4" drive)-either one can handle the job at hand. Before your next oil change, take your new filter down to the auto parts store and pick up the filter wrench that's right for you.

If you crank that thing down too hard and you may find yourself forced to destroy the filter bit by bit at your next oil change as you try to get the darn thing off. Remember, it's possible to also destroy the aluminum mounting point for the filter, so you have a lot more riding on the proper installation than having to try to force it off from just over tightening the filter.

Experience has shown that DC-4 is the key, so spring for that expensive tube of silicone grease that will last a lifetime.

Safety Wiring
Along with tightening the filter goes proper safety wiring. Some argue that you shouldn't safety the filter until after doing the run-up and leak check. Others believe that waiting till after the leak check is an open invitation to forget to safety the filter.

Either way, you've got to safety it with safety wire, and personal experience favors doing it before the leak check. Unless you've got the natural gift of being a great safety "wirer," chances are you'll be making some of the most common safety-wiring mistakes. Some you can cover-up quite easily and effectively. Others require starting over.

Just remember that a little practice will prevent problems in the future. For example, on the Champion filters with the safety wire holes at the top, the safety wire has a nasty habit of getting onto the rim of the filter can.

The result is that, when you think you're done wiring, you grab the wire and wiggle it, only to have it snap off the rim and go loose. One way to get around this is to tighten the filter to 20 ft-lbs initially.

Then, when the wire comes off the rim, you can simply loosen the filter a hair to tighten up the wire. The filter will still be within the specified torque range, and your safety wire will be good and tight. However, it should be noted that this is considered a sleazy trick, and it's worth your while to do the job right the first time.

One safety wire mistake that may require redoing the job is not putting enough turns in the safety wire (put too many in and you've got to redo it). If you haven't already twisted through the safety wire tang on the engine, you can simply put more turns in (there should be from six to 12 turns per inch of wire).

If you've already anchored the wire, and then notice there are too few turns; clip it all off and start over. As a side note, oil filter safety wiring among professionals runs the gamut from perfect to acceptable to downright laughable.

Another safety wire mistake is anchoring the wire to the wrong place. Most installations provide a tang with a hole through it somewhere near the filter base, while on others you've got to hunt down a good anchoring point.

Whatever you do, don't anchor the wire to the engine mount or it will snap on start up. And, if at all possible, use the provided tang. Sure, some of them are real pains to get to (the Cessna T-310 comes to mind here), but if the tang is there, use it.

You may find it easier to deal with getting the safety wire through the tang if you slip the wire through before mounting the filter. A final safety wire goof is doing it backwards. Remember that safety wire is supposed to keep things from loosening, so the wire should be pulling the filter (or anything else) in a tightening direction.

Oil Screens
Unfortunately, the engine makers were very slow to climb on the new technology bandwagon (and that hasn't changed much). In the late 60s, when disposable oil filters or even removable filter cartridges were widely available, very few engine or airframe makers were lining up to improve the engine filtration capability by a very significant degree.

In their defense, people flew far greater hours and corrosion and wear were not as big an issue as it is today. If you have a screen only in your engine, you can help prolong its life by switching to a filter.

There are many solutions out there from remote mount units to adapters that bolt to the case. The latter being quite reasonable expense-wise if you shop around a bit. There are at least four different sources, although they all don't make models that cover all engine types.

In any event be sure to clean your screen often, with 25 hours being the typical maximum time recommended by the manufacturers. The same holds true for finding any contaminants in an oil screen-save them as long as you own the engine and have them analyzed for both source and type.

Second OilPinion
One person that has more experience than any one we can think of in this arena is Howard Fenton. For decades he ran an oil analysis lab that we recommended. He now has a new, but related operation called Second OilPinion. He will analyze your filter element or any contaminants that you find doing it yourself. He can subject the contaminants to numerous chemical tests as well as use magnification to determine just what the source of the detritus in your filter or screen is made of and where it came from.

The price is extremely reasonable, so if you don't want to cut the filter open or are stumped by what you find, contact Howard Fenton at 918-492-5844, including how to ship.

By the way an interesting article is available on the Web at http://www.avweb.com/news/profiles/182855-1.html, which gives his background as well as his views on oil related topics. It's free.

The Run-up Check
The last, and perhaps most potentially fatal, mistake that people make when doing an oil and filter change (or any other engine work, for that matter) is not running the engine up and checking for leaks.

Think about it: Where would you rather be when you find an oil leak-on the ramp after running the engine for a leak check or at 50 feet after your next take off? So make sure you do a leak check and remember that the filter itself may be leaking from areas other than the adapter pad.

By combining this procedure with oil analysis, you will have a dual (and complimentary, not redundant) approach to the health of your engine and possibly yourself.



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