by Kim Santerre
You can argue about leaning procedures until youre purple in the face but everyone agrees that clean, fresh engine oil is better than dirty oil. Filters help keep oil clean and until recently, for paper filters, there was one choice: Champion.
Now comes Kelly Aerospace with its own filter design, aiming to topple Champions dominance.But does Kelly have a better filter? In our view, no, not yet. But neither Champion nor the upstart Kellys published ratings come close to the current filtration standard called out in industry technical specifications. (More on that below.)
Thats not to say the Kelly isnt a decent filter. Based on our dissections and research, the differences between the two arent so dramatic that the Champion is a walk-away winner.
In our view, theres lots of room for improvement in both filter brands in two distinct areas: filtration ratings and bypass ratings for filters with a built-in bypass valve designed for Continental engines.
Interestingly, despite both being sizable companies, neither Champion nor Kelly manufacture their own oil filters. Rather, they contract it out to companies. In fact, Champion recently changed vendors to make its new Champion version, known simply as the dash-1. Typical retail prices are $16.50 vesus about $13.50 for the Kelly models.
The new models keep the old CH48103, 4, 8, 9 and 10 model numbers but add a dash-1 to the number to signify the new model. When stocks run out, there will be no more of the old filters.
Paper oil filters showed up in the early 1970s, so obviously a standard acceptable to the FAA was required. It was published in 1975, based primarily on auto standards and called the Aviation Recommended Practices standard (ARP) for aviation oil filters.
Its some 47 pages of technical specifications published by the Society of Automotive Engineers. We obtained copies of both the 1975 and 1998 revisions.
For starters, if either Champion or Kelly fully met these standards, the filters would have a meets ARP standards label. Neither does. Both brands meet the majority of the standards sufficient to satisfy the FAA, but not sufficient to meet the SAE published standard.
In an effort to update and clarify a number of issues, the SAE published an updated version of the ARP standard in 1998. The most significant item in the revised standard was a specification for significantly improved and better defined micron filtration ratings and greater canister burst strength for the short version of the filter.
The old filtration standard was vague while the revised standard requires a 25-micron efficiency. Additionally, the new standard requires Beta ratio numbers, which means a more broadly accepted standard of accuracy in the micron ratings stated. Beta ratio-actually ISO standard 16887-prescribes a uniform, repeatable procedure to arrive at micron rating numbers. The establishment of Beta ratio is an attempt to improve the reliability and accuracy so buyers have some way to make valid comparisons between products.
Unfortunately, neither Champion nor Kelly chose to meet all the new micron standards of the 1998 ARP document. They avoided the updated standard by grandfathering their old products under the original ARP specs.
So despite being new, the original Kelly oil filter was approved based on the 14-year-old design of the Champ filter briefly marketed around 1990.
Champion has made meaningful improvements to its new filter. These include physical design improvements that, in some specs, exceed the newest ARP standard. For example, the case burst strength of the short case has been made more than 50 percent stronger and the mounting threads and canister nut have also been strengthened. Another significant improvement is that both the long and short filter versions are 1/2-inch shorter while diameter remains the same.
This means that the new filters will fit easier in some installations or even fit where they may not have fit before in tight engine compartments. Better yet, we verified that there are actually more square inches of filter media paper in the new models than the longer old models. This gives greater resistance to media saturation with contaminants and lower likelihood of going into bypass, which routes oil around a filter clogged with contaminants. (There are other reasons for bypassing, as explained below.)
One change in the oil filter base makes it difficult to cut for inspection, even if using the CT 470 cutter sold by Champion. You will either have to modify the cutter wheel upward about 1/16-inch or buy Champions soon-to-be-available filter cutter. If you try to cut a new Champion open without this adjustment, the cutter wheel will hit the solid steel base and may break if you force it.
The Kelly filters are a bit shorter than the old Champion, but not as short as the new Champion, so the nod goes to Champion for fit adaptability. Upon dissection, we found the filter media paper area in the Kelly to be about 20 percent less than the new Champion, meaning it could potentially saturate and go into bypass earlier than Champion. Again, the nod goes to Champion.
We were also troubled by the way the media is attached to the internal filter metal ends. An epoxy adhesive is used, but the flat end design lends itself to migration of the adhesive into the area where only filtered oil should go.
As long as the adhesive never breaks free, no problem. Kelly assured us that this was specifically tested as part of the ARP protocol and it passed. Champion uses a convex button that simply prevents any migration of adhesive, which we feel is a better design.
The case strength of the Kelly is on a par with the old Champion, which is to say adequate. Burst oil filters are a rarity, since the internal paper media is designed to collapse and tear at anything over twice the maximum oil pressure that an engine could achieve. This is still well below the filter case burst pressure of even the old standard.
The filtration ratios of both Champion and Kelly are 40 microns nominal according to their documentation and two independent tests which we reviewed, one by the Fluid Power Institute and another the Fluid Test Institute. The later is owned by SPX Filtran, which makes Kelly oil filters. Notwithstanding the vagaries of nominal micron ratings alluded to earlier, lets compare them to the latest 1998 ARP standard.
The new ARP standard calls for 25 microns and this may represent a significant improvement in potential engine wear compared to 40 microns. Its a given that the better the filter catches contaminants, the longer the engine will last-all other things being equal, which they rarely are. If you let your engine sit for weeks unflown or you change your oil only once a year, filtration ratings are meaningless drivel. Your engine will likely die of corrosion long before wear from use will be an issue.
Micron ratings are more important to those who fly regularly and change oil frequently. The more you fly, the more important filtration ratings become. Whats the big deal to increase the filtration ratings? The problem is that increased filtration capacity requires a beefing up of the entire design and probably a media type change to tolerate potentially greater internal pressures.
While it can be done, it cant be done without increasing price-perhaps significantly. And evidently, filter buyers are price sensitive. Some years ago, RAM Aircraft, the well-known performance house in Waco, Texas, designed and sold a clearly superior filter with a 10-micron rating, a 25 PSI bypass spring and a fiberglass-type media.
At $60 each, RAM didnt find enough buyers to sustain the product.
Inside the oil filters used on Continental engines so equipped, theres a built-in bypass valve designed to pass oil in the event of filter blockage for any reason. Lycoming builds their bypass valve into the engine, not the filter.
Bypass could be caused by cold, thick oil thats simply unable to pass through the media at start-up and for some unspecified time during warm-up. Another cause of bypass is a clogged filter media from dirty oil, prolonged filter change interval or something coming apart and clogging the filter media.
The engine manufacturer has to establish a point at which the bypass valve will open. Lycoming use 11 to 14 PSI differential while many Continental engine data sheets call for a 12 to 16 PSI differential, as well as a filtration rating of 20 microns, incidentally.
Strangely, both the Champion and Kelly filters are set at 8 to 10 PSI bypass, which suggests that cold oil is routinely bypassed, since this pressure spec is 50 percent lower than the engine maker recommends. The 8 to 10 PSI is the recommended minimum value in the ARP standard, which is inexplicable since its contrary to the standards published by Continental, the engine that uses the filter. Champion told us they had no idea of the Continental requirement and had us send them the Continental type certificate data sheets, which are available on the Internet.
Subsequently, Champion said Continental felt this was not a significant issue, but would not supply the name of the Continental spokesperson. Unfortunately, theres no reliable data to show how much additional wear is caused by dirty oil bypassed at such low pressures.
While Champions improved design is hardly revolutionary, we think it represents an improvement and we deem it the better choice of the two current paper filters available.
Its tough to knock a long-established competitor off the throne and although we think Kelly has offered a good first effort, their filter appears no better than the older Champion design. True, its a few bucks cheaper but we dont think that makes it a better value.
For frequently used, high-power or turbocharged Continental 470s or 520s, we think the ADC super screen is an option worth considering. Although expensive, the screen lasts essentially forever.
For whatever reason, Continental TSIO-550s dont have the same bypass valve or filtration requirements in their respective data sheets.
Worth noting, by the way, is that we found Kelly enthusiastically cooperative in answering our questions while Champion proved annoyingly difficult to work with. Keep an eye on Kelly. They may yet challenge Champion.