Piston Engine

Magnet in the Filter

When Aero Accessories founder and owner Tim Henderson decided to enter the market for piston engine oil filters, he looked for simple ways to improve the product. The most innovative feature that Henderson and his engineering team added to the filter is an internal magnet. Other features make the filter easier to remove and install and help ensure that it will endure the rigors of vibration, heat, and high-pressure oil.

"The magnet does two things," said Henderson. A typical oil filter's core is made of pleated 40-micron cellulose filter paper. Filters could be made with paper that allows only smaller particles to pass, he added, but the smaller the holes in the paper, the less oil will pass through the paper as the holes become clogged. And if the oil can't pass through the paper, it has to flow, unfiltered, through the filter bypass valve. So 40 microns turns out to be an ideal size, one that catches most of the particles that get created by combustion and wear but also large enough to allow oil to flow.

Tiny particles of steel, however, can easily be less than 40 microns in size and pass through the filter, according to Henderson. So the magnet acts as a secondary filter and catches and retains those particles, keeping them out of the oil and preventing further damage to the engine. "It's better than not having it," he said.

The other benefit of the magnet is that it's a useful indicator of metal-making activity in an engine. As mechanics get used to how many steel particles are deposited on the magnet between oil and filter changes, they will quickly spot excessive amounts and hopefully prevent impending engine problems.

The Aero Accessories oil filters have other, subtle changes. The nut on the end of the filter case is electrically spot-welded to the case; over-torque testing has shown that the case itself rips open and the spot-welds still hold. The nut is crimped in slightly at the base, where it meets the case. This helps keep sockets or wrenches from twisting off the nut while tightening and loosening the filter. To make safety wiring easier, the wire tabs at the base of the nut are bent up slightly to make inserting safety wire easier. The filter is designed to a 700 psi burst pressure, 200 psi greater than typical filters, according to Henderson, and the bypass relief valve meets Teledyne Continental's 12 to 14 psi specifications.

Aero Accessories manufactures the oil filters at one of the company's facilities in Gibsonville, North Carolina. Before setting up the plant, Henderson had thought that he would have to buy components from a supplier and hire a crew to do final assembly. But Mike Allen, a talented engineer, suggested to Henderson, "why don't we just build the whole plant?"

After gathering some specialized tools and adapting them to the peculiarities of oil filter production, Allen got the plant up and running. He incorporated some just-in-time and lean manufacturing concepts to make the operation efficient. For example, each of the five operations needed to make the filters is set up as a cell. But instead of employing people to operate each cell, he trained a team to perform all of the cell tasks. The team can move from cell to cell, depending on which portion of the filter needs work, thus optimizing the flow of material and keeping costs reasonable.

Another benefit of this small operation is that customization is easy. Aero Accessories is making a branded series of filters for parts distributor Aerospace Products International, with the API logo painted on each filter.

The filters, manufactured under FAA-PMA (parts manufacturer approval) regulations, started shipping in March. Wholesale buyers (FBOs, maintenance shops, and parts retailers) can buy the filters in buy-five, get-one-free six-packs. Filter size numbers are AA48103, AA48104, AA48109, AA48110, and AA48111. -- By Matt Thurber