DIY Wheel Bearing Service

DIY Wheel Bearing Service

A&P Jacqueline Shipe describes how to service wheel bearings in this article, the second in a DIY series for pilots who wish to take on preventive maintenance of their aircraft.

FAR 43 Appendix A lists the preventive maintenance items owners may legally perform on their planes. This list is fairly long—and some of the items are a little involved for a person to perform the first time by themselves, while other tasks on the list are pretty straightforward.  

There are several preventive maintenance tasks pertaining to the landing gear, including tire changes, strut servicing and servicing the wheel bearings. (Last month, Shipe discussed the steps involved in changing an aircraft tire. See the June 2016 issue for more information. —Ed.) 

A tapered roller bearing with pits on the rollers caused by corrosion due to water. 
Bearings: small but mighty

While cleaning and greasing wheel bearings doesn’t seem like too difficult a task, there are some guidelines that need to be followed. The failure of a wheel bearing can cause major damage to the wheel and can even allow the wheel assembly to slide off the axle.

Wheel bearings are relatively small, but are incredibly strong. They have to support the weight of the plane while allowing the wheel to spin freely in all types of temperatures and conditions. In addition, wheel bearings and races on airplane wheel assemblies also have to be capable of withstanding hard landings and both vertical and horizontal loads without failing.  

The race with lots of pitting; the race is in the process of being removed from the wheel half. 
Types of bearings

The bearings on most airplane wheel assemblies are the tapered roller-type. The outer part of the bearing is larger than the inner part, and the rollers are installed at an angle. 

The bearing itself rides in a metal cup called a race. The race has a “pressed in” fit in the wheel half, and is tapered on the inside to match the bearing. The biggest advantage of tapered bearings is the high load capacity that they can withstand. 

Automotive wheel bearings, on the other hand, usually use spherical rollers (i.e., balls). Ball bearings can withstand prolonged high speeds without building up too much heat, but cannot take high impact loads. 

Tapered bearings will bear up under the not-so-good landings that occur from time to time with an aircraft. In addition, proper servicing of these bearings will keep the wheels spinning freely and will last for a long time. 

The wheel half with the race removed. 
Removing the clips

Once a wheel assembly is removed from the axle, the wheel bearings are easily removed by taking out the metal retaining clips that secure the bearings and grease felts. 

There is an indention in the outer part of one end of the clip to allow a screwdriver to be used to pry it out. The clips don’t have a lot of tension on them and can be easily removed. 

Once the clip is off, the bearing, metal rings and grease felts can all be lifted out together. 

Be sure to keep all the rings and clips organized so they can be reinstalled into the same wheel half and in the same place. The metal rings that retain the bearing are sometimes slightly smaller on the outer half than the double rings used on the inner half, and can be easily mixed up. 

The race being installed. It has to be started evenly all the way around otherwise it will damage the wheel half as it is driven in.
Cleaning the parts 

A small bucket with 100LL Avgas works well to clean the bearings. Swishing the bearing around and spinning it by hand while it is submerged will clean all of the old grease and gunk out. 

The metal rings and clips should also be cleaned, but the felt material needs to be set aside; it should not be submersed in anything. There is really no way to clean the felt, anyway—as long as it is still in one piece, it’s good to go. Any grease felt that is torn or missing a section needs to be replaced. 

Once all the parts are cleaned, they should be blown out with compressed air (if available) or laid out on paper towels to dry. The parts need to be thoroughly clean and dry before fresh grease is applied.
Inspecting the parts

After the bearings, metal rings and clips are clean and dry, the bearing and race should be inspected for pitting or damage. If the race is smooth and has no corrosion, the bearing is generally corrosion-free as well. 

Races that have light surface corrosion can sometimes be smoothed out with a piece of light grit sandpaper (800 to start and 1200 to finish). Deep pits in a race mean replacement is needed. 

Discoloration on the bearing or race, such as a rainbow or gold color, can be a sign that these parts have generated excessive amounts of heat, in which case they should be replaced. 

The tiny section of aluminum at the bottom of the recess for the race is easily cracked if the race is driven in too far.  
Preventing corrosion

Wheel bearings typically fail for two reasons: corrosion or overheating. 

The greatest threat to airplane wheel bearings is usually corrosion. Almost all bearings and races will eventually require replacement due to water getting past the grease seals and accumulating in the bearing cavity, causing rust and pitting. 

When cleaning a plane, strong degreasers should not be used on wheel assemblies and wheels should never be sprayed with a water hose. The pressurized water will get past the grease seals and ruin the bearings. 

Folks that want their wheels clean can wipe them out with a rag that is lightly moistened with a little Gojo original white cream hand cleaner (the non-pumice kind). Then the wheels can be wiped clean with a dry rag. 

The back side of the wheel assembly should be closely inspected for any signs of cracking after a new race is installed.
Replacing the races

Wheel bearing replacement is easy, but replacement of the races is a little tough to do without the proper tools. 

Because the race has a pressed-in fit in the wheel half, it has to be driven out. This can be accomplished by using either a hammer and punch or a bearing driver tool. 

Occasionally a person encounters a wheel assembly with a race that has broken loose and is spinning in the wheel half itself. In this case, the wheel assembly has to be replaced; there is no permanent way to hold the race in place if the wheel assembly has lost enough metal that the race is no longer fitting tightly. 

The wheel is made of cast aluminum. When reinstalling the steel race, it is very important that it be driven in straight. If it gets cocked—even a little—the much softer aluminum will be gouged and damaged. 

The best tool for the job is a bearing driver, as it allows each blow of the hammer to be applied equally around the circumference of the race. 

Once the race is almost near the bottom of its recess, very light blows should be used to seat it in the wheel half. Many mechanics have driven the race in too far and cracked the fairly thin aluminum ring that retains the race. 

The wheel should always be thoroughly inspected for any sign of cracking on the front and back sides, whether or not a race is replaced.

A freshly greased bearing alongside its grease felt and retainer clip.
Packing the bearings and reinstalling 

Once all of the races are installed and the wheel halves are inspected, the bearings are ready to be packed and installed. A high-quality wheel bearing grease that has good water resistance should be used. 

The grease has to be pushed up through the bearing until it comes out the top between each roller. If it doesn’t squeeze through each opening, the inside of the bearing will have gaps and inadequate lubrication. 

It takes a little while to pack a bearing by hand. There are bearing packers sold in almost any automotive store that make the job a little faster and a little less messy. 

Once the bearing is packed, apply a layer of grease to the entire surface of the race to ensure it is covered as well. 

The bearing can then be reinstalled along with the correct order of retaining rings and grease felts. 

Lastly, reinstall the clip. It is a good idea to make sure the clip is pressed into place all the way around by pushing it outward with a screwdriver. 

After all the clips are in, the wheel bearing service is complete.

The greased bearing assembly installed in the wheel half. The wheel is ready for installation.
Jacqueline Shipe grew up in an aviation home; her dad was a flight instructor. She soloed at age 16 and went on to get her CFII and ATP certificate. Shipe also attended Kentucky Tech and obtained an airframe and powerplant license. She has worked as a mechanic for the airlines and on a variety of General Aviation planes. She’s also logged over 5,000 hours of flight instruction time. Send question or comments to . 
Camshaft & Lifter Wear

Camshaft & Lifter Wear

Corrosion attacks camshafts and lifters before most other bottom-end engine parts, especially when an aircraft doesn’t fly frequently. Learn how to prevent, identify and treat common camshaft and lifter problems before they cost you!

Many folks think of engine wear and tear and overall condition as being represented by the amount of operating time since the last overhaul. The “time since major overhaul,” or TSMOH for short, is typically entered by mechanics into an aircraft’s logbooks at every major inspection and annual. One of the first questions that buyers ask when considering an aircraft for purchase is “How much time is on the engine?”

Cumulative engine operating time does matter. Moving parts, particularly in the high heat and high stress cylinder environment, do wear with use. However, one of the main reasons that engines have to get torn down and rebuilt isn’t due to wear from operating regularly, but from corrosion that occurs during prolonged periods of non-use. 

An engine’s camshaft and lifters are particularly susceptible to damage from corrosion. Corrosion and the resulting wear on the camshaft and lifter bodies are one of the primary reasons engines get torn down before reaching the manufacturer’s recommended time between overhauls (TBO).

Lycoming crankshaft and camshaft gears as viewed from the accessory case section (rear) of the engine.
A Lycoming case half with camshaft installed, viewed from the rear.
Camshaft construction and function

Camshafts are a simple-looking part, but they play a major role in engine operation because they control and drive the entire valve train. The camshaft is gear-driven and typically turns at one-half the speed of the crankshaft. 

Camshafts are made of carbon steel and have varying numbers of “lobes” along their lengths. Each lobe has an elliptical shape and is put through a hardening process called “carburization” during its manufacture. 

The carburization process involves heating the camshaft in a specially-designed furnace or oven and exposing it to carbon monoxide gas as it is heated. This process causes the exposed surfaces on the camshaft (primarily the lobes) to absorb extra carbon, which makes the surface of the lobes very hard. The depth of the hardened layer on the lobe is about .015 inch (fifteen-thousandths
of an inch). 

The hydraulic lifter units from a Continental C-85 engine.
The valve train components: camshaft, lifter, pushrod, rocker arm and valve.

A solid Lycoming O-235 lifter.
Lifter construction and function

The lifter consists of a cast-iron outer body that houses a hydraulic unit. There are a couple of Lycoming engines that still utilize solid lifters with no hydraulic unit, but the vast majority of engines have hydraulic lifters. Most mechanics use the term “lifter” when referring to both the lifter body and the hydraulic unit inside the body. 

Lifters are also sometimes referred to as “tappets.” The face of the lifter body is the part that is in continuous contact with the camshaft lobe that it rides on. The lifter face is made of chilled cast iron which gives it increased wear resistance. It is tough, but not nearly as hard as the carburized surface on the cam lobe. 

The lifter is designed to be a little softer than the lobe, so that the two are compatible with each other. If deterioration does start to occur, it generally occurs first on the lifter rather than the camshaft lobe. 

The hydraulic unit in the lifter body is designed to act as a solid unit as it opens the valve. It must also be able to expand or contract as needed to take up all extra clearance in the valve train. There are some variations in the exact design, but the basic function is the same. 

The interface between the camshaft lobe and lifter body is under very high pressure and is unforgiving of any defects.
A corroded camshaft lobe.
A Continental O-470R camshaft shown installed just above the sump. The lobes on this camshaft all exhibited normal wear patterns; engine was torn down due to time. not corrosion.
Valve operation

The cylinder valves are linked to the camshaft through the lifter, push rod and rocker arm. The camshaft rotates and the top of the lobe raises the lifter to its highest point. The push rod in turn raises the rocker arm end to which it is joined.

Since the rocker arm is mounted near its center on a steel shaft, it acts as a fulcrum and raising one end causes the other end to lower. The opposite end of the rocker arm that is in contact with the top of the valve stem then lowers the valve to its full open position. 

The time that the valve opens in relation to all other moving engine components, and the length of time that it stays open are both determined by the height and position of the camshaft lobe. 

The valve clearance, or valve “lash” as it is often called, is measured with both the exhaust and intake valves closed with the piston at top dead center (TDC) on its compression stroke. The clearance is measured with the hydraulic unit of the lifter “bled down,” or in its flattest position with no oil in the reservoir of the lifter. 

The clearance is checked between the valve stem and rocker arm with the push rod socket on the rocker arm pressed in toward the camshaft. The engine manufacturers set a minimum and maximum clearance for the valves. Too much or too little clearance can cause increased wear on the valve operating mechanism. 

The clearance is adjusted on engines with solid lifters by means of an adjustment screw on the rocker arm itself. On engines with hydraulic lifters, the adjustment is made by replacing the push rod with another of a different length. 

The valves are held in the closed position by multiple strong valve springs. The camshaft and lifter must overcome the valve spring tension every time the valve is opened. This generates a large amount of pressure between the lifter face and the camshaft lobe. 

A Lycoming O-235 case half with the camshaft in place (above) and with the camshaft removed (below) to show where it rotates.
A Lycoming O-235 case half with the camshaft in place (above, left) and with the camshaft removed (above, right) to show where it rotates.
A severely spalled lifter face.
Lifter spalling

The camshaft and lifter bodies typically are lubricated in most engines by what is called “splash lubrication.” There are no pressurized oil ports on standard engines that deliver oil to the cam and lifter surface; they run only in the oil that is thrown off the crankshaft and rods as they rotate. 

At engine start-up, it typically takes a few revolutions of the crankshaft to begin getting any significant amount of oil to the camshaft. The lack of pressure lubrication along with the high pressure between the interface of the camshaft lobe and lifter face create an environment that is unforgiving of any defects in the surfaces of either the lobe or lifter. 

Engines that sit dormant for extended periods of time (between two to six months, depending on the environment) are subject to developing corrosion on both the lifters and on the cam lobes themselves. 

The camshaft on Lycoming engines is located in the top of the crankcase above the crankshaft. Its position in the top of the case means that oil drains off it first once the engine is shut down. On Continentals, the camshaft is located beneath the crankshaft, but it is still above the oil sump and residual oil eventually drains off it as well. 

The crankshaft is not as vulnerable to corrosion because its metal-to-metal contact surfaces are encased in bearings. The bearings typically hold a film of oil on the crankshaft surface. The camshaft has no bearings. It spins inside machined grooves in the crankcase. The lobes and lifters have a lot of their surfaces fully exposed to the air that drifts through the engine. 

Aircraft engine breathers are simply vents designed to prevent pressurization of the crankcase with the engine running. However, they also vent and expose the internal engine components to any humidity that may be present in the outside atmosphere as the airplane sits parked.

Condensation occasionally occurs inside the engine after shutdown as parts of the engine cool at varying rates. Condensation also occurs with different weather conditions during times of non-use. Moisture can cause small freckles of rust to form on the lifter face. As the corrosion progresses, the rust eats into the lifter surface. 

Once the engine is started again, the small patches of rusted material fall out as the lifter face is pressed against the camshaft lobe. After this process starts, the constant pressure between the cam lobe and lifter wears off more and more material even though the engine is being lubricated during operation. This process is referred to as “spalling” of the lifter. 

The removed material and the rough lifter face will eventually wear the camshaft lobe. If lifter spalling is caught early, the problem may be fixed by replacing the affected lifters. However, if any of the camshaft lobes have begun to wear, the entire camshaft—in addition to the damaged lifters—must be replaced. 

A lobe on a Lycoming O-235 camshaft that has been damaged from a spalled lifter.
The spalled and corroded lifter face.
Lifter inspection on Continental engines

Most Continental engines use cylindrically-shaped lifter bodies that can be removed without splitting the crankcase. Lycoming engines use mushroom-shaped lifter bodies that have a larger diameter at the face of the lifter. These types of lifter bodies cannot be removed without splitting the case. 

On the larger Continentals (O-470 series, IO-520, etc.), lifter removal only requires removal of the affected cylinder valve cover, rocker arm, push rod and the push rod housing. The housing is removed by compressing the tension spring on the inboard part of the housing to release it. 

Once the housing is out of the way, the lifter can be removed by gently using a pick to grab it by the oil galley in the push rod socket and sliding it out. Engine manufacturers do not recommend using a mechanic’s magnet to remove a lifter because it could magnetize the ball in the check valve of the hydraulic unit and cause the valve to malfunction.

After the lifter has been removed, the camshaft lobe can be inspected using a bright light. Continental Service Information Directive SID 05-1B contains inspection criteria which should be used to determine if a camshaft is still airworthy. Continental recommends using a mechanic’s pick to probe any surface deformities. 

If the pick catches, the camshaft most likely will need to be replaced. If the camshaft lobe looks OK with no surface damage, the lifter itself can be replaced with a new one if it shows any sign of wear. 

Some mechanics are leery of replacing lifters without replacing the camshaft because the lifters and cam lobes do wear into each other slightly during the initial engine break in, but it is primarily the lifter, not the camshaft lobe that wears. 

Aircraft owners who have large Continental engines that have been dormant for an extended period of time would be wise to inspect their lifters before they run the engine again. The process of doing so may very well catch a corroded lifter before it has a chance to wear a cam lobe. Six months would be considered an extended period of time under usual conditions; two months in humid or salty areas.

A Continental O-470 cylinder with one of the rocker arms and pushrods removed and the push rod housing partially removed.
Clues that a camshaft may be wearing

Most camshaft and lifter wear goes undetected until fragments or small magnetic filings show up in the oil filter during an oil change. Even though amounts may be very small, the camshaft and lifter bodies are usually the culprits if an engine suddenly starts making magnetic material. Steel cylinder barrels or steel cylinder rings also are prone to rusting a little, but they generally stop shedding any rusted debris as soon as the airplane is flown a time or two. 

Regularly-occurring magnetic filings are most likely coming from the lifter bodies, and once lifters start shedding surface material, they continue to degrade and wear with subsequent use. The good thing is that other than possibly causing a tiny bit of engine roughness, cam lobe and lifter wear is not something that causes sudden stoppage of an engine. 

If small amounts of filings are found, the oil filter element and its contents should be sent to an aviation oil analysis lab to determine the source. An oil-only analysis will probably show nothing unusual in these cases because when the lifters start spalling, the flakes and filings they shed are so large that they get caught in the filter rather than being suspended in the oil itself. Most labs can examine the filter element itself to determine where the metal is coming from. 

Some mechanics that find very small amounts of magnetic material (less than enough to cover the end of a mechanic’s magnet) will recommend flying the plane for another 10 hours or so, then checking the filter again. The hope is that it will stop on its own, but an engine that is past the break-in period should not be making magnetic material. 

If the filings are coming from rusted cylinder barrels, an owner might get lucky and the oil filter might be clean on the next check, but it’s been my experience that almost every time I’ve found magnetic debris in the filter, it only gets worse and worse with use. 

An O-470 cylinder with the push rod housing; the housing is removed by releasing the spring tension.
A severely worn camshaft lobe.
A Continental IO-520 with the cylinders removed. The lifter inspection is easy with the cylinders off because the lifters can simply be slid out.
An O-470 push rod and shroud.
Reground versus new camshafts

A camshaft or lifters that are worn badly enough to necessitate an engine teardown will require replacement. Many engine rebuilders in the field have no problems using a reground camshaft (one that was still within serviceable limits that has the lobes re-machined to a smooth finish.) Lifter body faces can also be reground to a smooth finish. 

If an owner chooses to use a reground camshaft or lifters, they should only get them from a high-quality aircraft machine shop experienced in the regrinding process. The carburized hardened layer on the camshaft lobes is only around .015 inch deep, and the layer’s depth can vary a little. 

If a machine shop accidentally gets below the carburized layer at any time during the regrinding process, the camshaft lobe will wear down rapidly once it is put back into service. The initial hardening process of carburization is completed only at manufacture. It can’t be duplicated in the field because it is almost impossible to keep the camshaft from warping during the carburization process. 

Additionally, the apex (or top) of the camshaft lobe is tapered slightly. One side of the lobe is slightly (around .003 inch) higher than the other side. This design causes the lifter body to spin as it contacts the lobe. This prevents the camshaft lobe from contacting the lifter face in the same place every time, and helps prevent wear on the lifter face. The exact taper may be hard for some shops to duplicate.

I personally would rather have a new camshaft and lifters if the engine is being torn down to the extent that they were accessible. However, most reputable engine builders that I spoke with had no problem using reground cams and lifters, depending on where they were done, and I know of more than a few engines that have easily made and even gone past TBO with reground parts.

A Continental IO-520 with the cylinders removed. The lifter inspection is easy with the cylinders off because the lifters can simply be slid out.
A severely spalled lifter out of this engine; it ruined the camshaft lobe it was riding on.

The best thing an owner can do to prevent camshaft and lifter problems is to regularly fly his or her plane—at least once a week in humid climates. Each flight should be long enough to get the oil temperature up to at least 180 degrees to evaporate any water in the oil system. Changing the oil regularly and often is a good preventative maintenance practice. The addition of an anti-corrosion additive also helps. 

The initial cost of prevention generally is greatly rewarded with a long-lasting healthy engine. 

Know your FAR/AIM and check with your mechanic before starting any work. Always get instruction from an A&P prior to attempting preventive maintenance tasks.

Jacqueline Shipe grew up in an aviation home; her dad was a flight instructor. She soloed at age 16 and went on to get her CFII and ATP certificate. Shipe also attended Kentucky Tech and obtained an airframe and powerplant license. She has worked as a mechanic for the airlines and on a variety of General Aviation planes. She’s also logged over 5,000 hours of flight instruction time. Send question or comments to .


TCM Service Information Directive 05-01B, “Inspection Guidelines for CM Camshafts and Hydraulic Lifters” 

Anti-corrosion additives
AvBlend – CFA supporter

ASL Camguard

Oil Changes: The Original DIY

Oil Changes: The Original DIY

A&P Jacqueline Shipe details the process of changing the oil and filter on an aircraft in this fifth installment in Cessna Flyer’s DIY series.


Most planes have a drain valve to facilitate oil changes. There are two primary types of valves: the style that pushes straight up to lock in place, and the type that has to be pushed up and turned.

One of the items that is labeled as preventive maintenance by the FAA that a pilot may perform on his or her own airplane is the cleaning or replacing fuel and oil strainers or filter elements.

An oil change performed at a regular interval is one of the best things that can be done to prolong engine life. Clean oil lubricates and carries away harmful deposits better than dirty oil; plus, inspecting the contents of the removed filter or screen often helps to detect a malfunction before it becomes catastrophic. 

Draining the oil

Warm oil drains faster than cold oil, so it is nice to run the engine a little before beginning the oil change to cut down on the amount of time it takes to drain. (If you choose to do this, remember that the exhaust components will be especially hot. Use care.) 

The first step in the oil change process is draining the old oil. The container the oil is being drained into needs to be large enough to accommodate it. An old five-gallon bucket works well. 

Most planes have a drain valve on the bottom of the sump to facilitate oil changes. There are two primary types of valves: the style that pushes straight up to lock in place, and the type that has to be pushed up and turned. 

If it is possible to reach the valve through an opening in the lower cowling, an old rubber hose that fits snugly over the drain end of the valve works great to port the old oil into a bucket and saves having to remove the entire cowling. (It makes a huge mess if the hose pops off the drain valve midstream, so be sure it is secure.)

If the valve is inaccessible, the lower cowling will have to be removed, which isn’t such a bad thing because it allows access to give the engine a good looking-over. 

The space between the filter and the other parts on the accessory case is very limited on some engines, like the one above; a short wrench may be required in these situations.
This black rubber drain hose is inserted through the cowl flap onto the drain valve on the sump in order to port the old oil into a bucket.
Removing the filter

Filter removal begins with cutting the old safety wire. The wire should be cut in the loop that goes through the safety hole on the engine, never pulled through. 

If the wire is pulled, it will cut through the soft, very thin tab on the engine and the tab will then be useless. Once this happens, the safety wire has to be attached at another point on the engine. 

After the safety wire is removed, the filter is loosened by using a one-inch size wrench on the end adapter to remove the filter. It is best if the wrench is the six-point style because the adapters are fairly thin; if the filter is stuck on the engine from being overtightened the time before, a lot of torque will be required to break it loose. The ears on the adapter can be easily rounded off if this happens. 

The space between the filter and the other parts on the accessory case is very limited on some engines; a short wrench may be required in these situations. 

The filter usually drains a little oil as it is removed. An empty oil container turned sideways with the top cut off can catch any oil that dribbles out as the filter comes off. Once the old filter is off, it can be placed aside and allowed to drain.

This filter has been cut open, and the inner part is being lifted out of the housing. The paper pleats in the inner part have to be cut out of the inner metal housing with a utility knife and spread apart to be thoroughly inspected.
Installing the new filter

The new filter needs to be double-checked to be sure it has the correct
part number. 

Some folks jot the tail number and tach time on the side of the filter using a permanent marker when it’s installed. This helps to determine when the oil was last changed without having to drag out the logbooks. It also ensures that the old filter won’t get mixed up with one that came off another engine or airplane. 

The new filter also needs to be inspected to be sure there are no leftover pieces of packaging or debris laying in it. If the filter has any dents or other signs of mishandling, it should be discarded or returned. 

After the filter is inspected, the gasket should be lubricated to protect it during installation. Some mechanics also partially fill the filter with clean oil before it is installed to help prevent a dry startup. 

Dow Corning DC-4 is the lubricant most filter companies recommend for greasing the gasket on the filter prior to installation. The lube helps with removal the next time, but mainly it keeps the rubber seal from being broken loose from the filter during installation. It usually costs around twenty bucks for a tube of this lubricant, and one tube can last for several years.

The oil filter adapters are designed to provide a place to grab the filter with a wrench and are spot-welded on during the manufacturing process. If the new filter is overtightened during installation, one or more of these spot welds may break loose, which can cause a severe leak initially or later on down the road. 

Some mechanics never use the wrench adapter to install a filter because of this. At any rate, care should be taken to not overtorque the new filter. 

Once the new filter has been installed and properly tightened, it is ready for safety wire. Wherever the new wire is routed, it should be situated so that it can’t chafe into the filter or into anything else. Some mechanics slip a piece of heat shrink or something similar over the new wire to help prevent it from rubbing into the filter. 

The wire should have a positive pull on the filter and be fairly taut. 

An oil screen screen is safety-wired in the same manner as a filter. The screen shown is on a Continental C-85 engine; the oil temperature probe screws into the back.
Shown above are the new and old style piston pin plugs. The top one has the plugs that screw into the pin, while the old style (bottom half of photo) is the type that has the plugs that butt up next to the pin. All three pieces of the old style plug are supposed to be able to slide from side to side, and are contained by the cylinder wall. The plugs on this old style pin can sometimes develop significant wear in a short time if they get hung in a fixed position.
Service the oil screen

Oil screens are removed in a similar fashion as an oil filter. The screen is small (compared to a filter) and generally has a larger area for access. The screen is safety-wired in the same manner as a filter. 

A copper crush washer is used as the seal on the oil screen housing, and the crush washer should be replaced at each oil change. 

Engines that didn’t originally come with an oil filter as standard equipment and have an aftermarket oil filter kit installed often will have the original screen as part of the oil system. 

The oil screen should be regularly removed and cleaned in addition to replacing the filter on these engines because the dirty oil goes through the screen before it reaches the filter. If it’s neglected, the screen can actually become clogged with debris and restrict oil flow to the engine.

This severely worn piston pin plug (left) has almost completely disintegrated. A standard piston pin plug has been placed on the right for comparison.
Perform a leak check

Changing the oil and filter is fairly straightforward, but there are some precautions to take. The oil pressure at the point where it flows through the filter or screen is very high; a leak in a gasket can quickly lower the oil level if the airplane is flown with a leaking filter or crush washer. 

Any time the oil filter is replaced or the oil screen is cleaned, the engine should be run on the ground afterward and then checked for leaks. After the proper oil amount is added, the engine is ready for a ground run and leak check. 

Average wear of an old style piston pin plug will look similar to what you see above.
Inspecting the oil filter and/or screen

The contents of a removed screen or old filter should always be thoroughly inspected for any metal. A clean white paper towel works well to catch the residue off a screen as it is cleaned. Most mechanics use a solvent or parts cleaner to flush a screen. 

An old filter should be cut open using a filter cutter so the inner part of the filter can be removed. The paper element needs to be completely cut out of the inner metal housing and unfolded so it can be inspected. 

When the pleats are still wet with oil it can be hard to see very small particles embedded in the paper. Some folks let the filter drain overnight because of this; the element can be folded sideways and compressed in a vice if a person is in more of a hurry. A vice will squeeze out the old oil but leave any contaminants in the pleats. 

A magnet gently drug across the filter pleats or the paper towel will pick up any steel particles. Finding any metal is cause for concern, but finding steel contaminants is a major concern. The source of the steel should be tracked down and remedied if there is more than a trace amount. 

Aluminum flakes or slivers are generally caused by wear on one or more of the piston pin plugs in the cylinders. These plugs are made of aluminum in most engines; some are now made of brass. 

They contain the free-floating piston pins on either side and keep them from contacting the cylinder walls. Aluminum and brass are relatively soft compared to steel and are designed to wear without damaging the cylinder wall. 

If just a few particles of aluminum or brass are found, it is best to change the oil at an earlier interval next time in order to inspect the filter contents. Generally the problem goes away on its own because the plug wears itself in a little and stops, but not always. 

Increasing amounts, or large initial amounts, of any metal is grounds for disassembling the cylinders—and possibly the entire engine—to discover the cause. It is best to let an experienced mechanic inspect oil filter contents if any metal is present to get a second opinion about what action, if any, should be taken.

Regular oil changes will save money in the long run. Owners that change the oil, filter and/or screens themselves will not only save money on labor costs, but also have a good understanding of the health of their airplane engine.

Know your FAR/AIM and check with your mechanic before starting any work. Always get instruction from an A&P prior to attempting preventive maintenance tasks.

Jacqueline Shipe grew up in an aviation home; her dad was a flight instructor. She soloed at age 16 and went on to get her CFII and ATP certificate. Shipe also attended Kentucky Tech and obtained an airframe and powerplant license. She has worked as a mechanic for the airlines and on a variety of General Aviation planes. She’s also logged over 5,000 hours of flight instruction time. Send question or comments to .