by Kim Santerre
Its often been said that the only thing an engine oil screen is good for is catching things with part numbers on them. Perhaps a bit of hyperbole, but if you have an engine that doesnt have a spin-on oil filter-and a surprising number dont-there are compelling reasons why you should install the hardware to add one.
Theres no question that cleaner oil is better than dirty oil. And cleaner oil is almost certain to make an engine last longer and reduce maintenance incidence. Screens were placed on engines in lieu of paper filters because that was the best idea at the time and paper filtration wasnt as advanced as it is today.
Most owners can make the change to a spin-on filter for between $229 to $475 for parts, with an easy installation. The installation must be made or supervised by a certified mechanic for certificated aircraft. Then a logbook entry is made or, where the installation is per an STC, an IA must inspect the job and sign off a FAA Form 337, which is filed with the FAA. (This is not a field approval request, just routine recordkeeping.)
Why Do It?
The value of filters over screens is not just our point of view. We polled several IAs, including overhaul shop owners such as Charlie Melot, owner/operator of the highly regarded Zephyr Aircraft Engines of Zephyrhills, Florida. He agrees that its well worth the bother of adding a filter adapter but qualifies his recommendation with the advice that owners should still stick to 25-hour oil changes, even with a filter. Other IAs we spoke to agreed that the value of the filter over the screen and frequent oil change intervals is worth the investment.
Parts sources for this conversion are available from both the OEMs as well as the aftermarket. Theoretically, the oil change hourly interval is essentially double when you install a paper spin-on filter, but we agree with Melots recommendation to adhere to 25-hour intervals unless you fly over 200 hours a year and the airplane is always on the go.
Conversely, the 25-hour recommendation assumes that you fly often enough to pass the standard oil screen 25-hour change mark in less than three or four months, a typical recommended oil change calendar time interval with filter or a screen.
The best reason to go for a spin-on filter is the superior filtering capabilities and likely beneficial effects in improving engine life. Further, on most engines, changing the oil will be easier with a spin-on filter than it is with a screen, which must be removed and cleaned. Engine longevity should be compelling enough to add the filter adapter, but if you fly less than 50 hours a year, its likely that corrosion will get your engine before better filtering will extend its life. You might be further ahead to just keep the screen and do three-month oil change intervals.
A long-sitting engine not properly pickled is one thats slowly dying of internal corrosion. It may fire up and seem to run fine after a long sit but that doesnt mean that significant damage hasnt occurred. Early engine overhauls often follow after long-term sitting. The engine teardown almost always shows lots of serious internal corrosion to components that might not have needed replacement if the engine had been flown regularly.
With respect to oil filter adapters, there are at least two ways to go: direct mount filter adapters that bolt right to the engine and remote mount adapters that bolt somewhere else. In addition, you can choose to use an aftermarket screen in place of a regular spin-on, disposable oil filter. Well examine the pros and cons of these methods in this article.
Why do we have screens in engines to start with? Its a simple matter of economics, space in the engine compartment and the thinking at the time. Fifty or more years ago, when the vast majority of aircraft engines were designed, oil filter use and superior filtering were not a common or long-proven technology and entailed added cost and space.
Oils were basic in those days and screens were a simple and cheap way to go. They were primarily designed to catch metal, not filter dirt from the oil. Engine TBOs were much shorter, oil was cheap and it was believed that a screen was sufficient for the task at hand. There was a subsequent interim period where a disposable filter element inside a permanent canister was used in some engines before the disposable spin-on became widely available.
As experience with the disposable elements showed favorable results over screens and the spin-on became readily available, the OEMs made retrofit filter kits available. Unfortunately, the retrofit units fit only a limited number of engines due to their straight design and tight fits in many instances.
An oil screen will typically filter contaminants as small as 60 microns, but not much smaller, at least in significant quantity. The screens sold as aftermarket filters can allegedly catch some contaminants to 3 microns, but we feel this provides little added protection, since this is smaller than the space between the bearings. A nominal oil film between bearings is .0015 inches and this equates to about 38 microns.
The actual range of contaminants that have the most deleterious effect on an engine will vary according to which text you read. Generally, the range of 25- to 60-micron contaminants is considered the most harmful to a piston aircraft engine.
A human hair is between 40 to 70 microns as a frame of reference; the human eye can discern 40 microns. Disposable, spin-on filters generally trap the contaminants in this range best. Considering the 60-micron capability typical of OEM screens, they miss much of the worst stuff. That said, filters and screens actually improve with use as they trap particles and fill in some of the gaps, so to speak, between the screen or paper mesh after multiple oil passes. Filters also do something the screens dont: they trap moisture in oil at initial start-up.
There are a number of other factors affecting oil performance. This includes the additive package in the oil, whether its synthetic or organic or a blend, the general health of the engine, how hot the engine/oil is operated, the specific tolerances of a given engine, whether its turbocharged and the operating conditions of the engine. (We have seen engines ruined by a leaking air filter.)
Operating from dusty runways is more likely to contaminate the oil faster than not, for example, as is infrequent flying. The point is, there are lots of variables at work here besides oil filtering that can have an effect on engine longevity. A filter alone is not a magic bullet for longevity.
Fortunately, the aftermarket saw an opportunity in the form of more versatile oil filter adapter kits that can fit most applications. Thus, Continental, Lycoming, Franklin and some radial engines now have aftermarket adapters available-remote mount filter models only, for some. Some direct-mount adapters come with 45- or 90-degree angles built in so theyll fit more existing aircraft engines/airframe combinations.
Other aftermarket models are exact copies of the OEM optional adapter, for about half the cost. Still others have remote mounting of the filter-often on the firewall-when space is an issue. There are also fine-mesh remote mount aftermarket screens available from sources detailed below.
For oil filter adapters, legal approvals are largely a non-issue, since FAA STC approvals have been granted to the bulk of Continental and Lycoming engines, plus Franklin and some radials. In most cases, you can find an adapter that will fit. If theres any question, talk to an aftermarket supplier, all of whom seemed knowledgeable on various applications. All the filter adapters we looked at and the two we installed (B&C and Niagara models) carry FAA/PMA and/or STC approvals, if needed. There are a few cases where some minor mods will have to be done for engine compartment clearances on some airplanes.
For B&C and F&M products, STC and Form 337s, plus logbook entries, are required for certificated aircraft. The Niagara Airparts model can be installed with just a logbook entry, since its a duplicate of the factory optional part that can be found in the specific engine model parts manual.
If you have other optional gear installed, check with the adapter maker to see if there are clearance issues. Add-on oil coolers are something that might create a clearance or interference problem. Last, there are no ADs against any of these aftermarket adapters. There are at least two ADs on factory filter set-ups.
Fortunately, the aftermarket often sees profits in OEM oversights and we like these aftermarket adapters as the most cost-effective approach. Prices we quote are from the Aircraft Spruce online catalog; you may be able to find a better deal.
For Lycomings, if you have the space, Niagara Airparts makes an exact FAA/PMA copy of the Lycoming adapter for $229, while the Lycoming part is $449 from Chief Aircraft Parts. Lycoming special service publication 885-1 will help familiarize you with the installation if youd like to see whats entailed. If your Lycoming parts manual lists an adapter as an option, as most do, all thats needed is an A&P signoff in your logbook. But be sure to verify that your engine is eligible in the OEM engine parts manual for the part.
If tight space is an issue, B&C makes a beautiful, machined aluminum billet 90-degree angle adapter for Lycomings that fits in very tight quarters (see photo examples). Price is $440 with STC or $385 without it, for home-builders who dont need the paperwork. B&C also makes a model for Robinson helicopters.
Additionally, the company has several different spacer plate thicknesses available for especially tough fits to clear other engine components. If you have a tricky installation problem, call B&C for advice. Theyll help you with your fit problems; just ask.
For Continentals, F&M makes a cast aluminum adapter available in a number of different configurations for the more varied Continental engine series designs. Theres also a model sold by El Reno Aviation, which has been around for quite some time, providing adapters sold for the older Continental-powered Cessna 150s.
The oil filter adapter sold by El Reno is actually manufactured by F&M and marketed by El Reno as well as F&M. El Reno also has an oil temperature probe adapter for aftermarket temperature probes for O-300 Continentals whose owners want to add an F&M adapter. The Cessna 175 with a Lycoming GO-300 will need to use a remote unit, due to firewall proximity. If you have a Cessna 182 with an O-470 and firewall stiffeners, theres a fit problem. F&M recommends that you contact them for alternatives. Their adapter will not fit C85-8 or C90-8 engines. The F&M models range in price from $224 to $412, depending on engine.
Because of added complexity and expense, we recommend remote-mount filter kits only when either the B&C or F&M adapters are not authorized by their respective STCs. Remote mounts move the filter assembly itself off the engine proper and place it somewhere else in the engine compartment, normally the firewall. An issue with the remote units is proper mounting on the firewall for the remote oil filter component, which is not as easy to do as one might think.
To prevent cracking from metal fatigue of the thin firewall material, there may need to be additional firewall strengthening in the form of a doubler or other filter support measures. A stuck filter has caused firewall cracks that originated with manhandling during filter removal. Vibration of the filter can also cause cracks.
Hoses are another problem with the remote mounts. Weve seen cases where ordering improper hose lengths has been a costly mistake for the installer. A single angle hose fitting can cost $45 and a single hose can cost more than $100, with two required. And no hoses come with the Airwolf kit. Theyre a separate expense.
Airwolf is the biggest player in the field of remote mount units. They have models and STCs for many engines, including Stearmans and T-6s. Their products are top quality, but be prepared to pay. For example, compare installation costs for a Lycoming O-320. You can get a Niagara Air Parts direct mount adapter for $229 (provided you have the space), which could be typically installed quickly by an A&P with only a logbook entry.
The Airwolf remote mount adapter for the O-320 would cost $474, plus hoses (available from Airwolf), fabrication and routing of oil lines, as well as 337 preparation, inspection, sign-off by an IA and 337 recording with the FAA.
Both the Niagra and Airwolf use the exact same Champion filter. Airwolf kit prices run from $385 to $809, depending on engine model. But if you didnt have room for the straight Niagara Airparts adapter in the above example, youd have to go with the more expensive direct mount B&C for $385. Still, youd save the cost of remote oil lines, which can easily add well over $150 to the installation, just for parts. If you do elect to go with oil hoses in a remote kit, be sure to specify steel fittings over aluminum. These are the safer choice for the engine compartment.
Aviation Development Corporation (ADC) is another remote filter mount and special filter design company marketing both a screen rated at 25 microns absolute, as well as a standard remote-mount Champion filter system.
Their STC models fit many engines. Prices run from $479 to $645 for aircraft with screens, depending on application. The ADC system also has an oil bypass detector alert for the cockpit and the construction quality of this system is quite impressive.
The ADC system also has chip detectors (magnets) that will warn the operator of ferrous metal chips in the oil. This chip detector is an extra cost item that can fit into the oil filter adapter or be installed on its own on the engine pan. The best spot is right in the oil drain plug.
Add an oil filter adapter, if you can, to replace the pressure screen you may currently have. We consider this to be a good investment if you fly more than 50 hours a year. Buying aftermarket oil filter adapters will save money and we think paper filters are a better bet than the aftermarket screens.
Adding a remote mount filter kit should only be considered if theres no way to access a retrofit engine mount type oil filter kit. In the case of the remote units, youll generally have the most flexibility with installation, but it will be the most costly. Be sure the installer is familiar with the process, orders hoses correctly and properly beefs up the firewall to preclude any cracking.
Dont look at these oil filter adapters as a way to prolong oil change intervals, but as a way to extend the life of the engine. If you fly a lot, 250 to 400 hours a year, say, then 50-hour change intervals make sense. A secondary benefit is cleaner and faster oil changes with a filter.
Before adding the Niagara or factory adapter, be sure that its authorized for your specific model engine in the parts manual or a factory bulletin.
For the STC adapters, be sure your engine model is covered by the STC and that you dont have other STC installations in your engine compartment that may interfere. Once you have a filter installed, be sure to cut it open at each change to check for contaminants.
• Niagara Air Parts, 800-565-4268, www.niagaraairparts.com
• B&C Speciality, 316-283-8000, www.bandcspecialty.com
• F&M Enterprises, 888-317-5222, www.fm-enterprises.com
• Airwolf Filter Corp., 800-326-1534, www.airwolf.com
• Aviation Development Corp., 800-944-3011, www.aviationdevelopment.com
-Kim Santerre is editor of Light Plane Maintenance magazine.