Alignment aids for Lycoming oil screen housings.


Part of changing the oil in my Lycoming aircraft engine requires removal of the oil screen housing and checking to see if and how much metal appears in the washed screen sediment. The oil screen housing is located below the vacuum pump, and the space between the housing and engine firewall is limited. It is difficult to hold the screen, line-up the bolts with four holes, and insert the 1/4-20 bolts into the threaded holes in the accessory case. To eliminate the alignment challenge, I cut a piece of 3/32-inch diameter brass tubing (K&S Metals #8155) into a pair of 4-inch-long pieces. If each pin is inserted into one of the two top accessory case threaded holes, and if the oil pressure screen housing is slid over these alignment pins until firmly against the accessory case, the insertion and tightening of the bottom bolts is very easily achieved (followed by the upper bolts).

Other materials may be used for the alignment pins such as steel or aluminum rod. However, aluminum may not provide sufficient strength. Selecting the diameter of the rod is a tradeoff. If you select too small a diameter, the rods will fit too loosely in the holes and the pins will wobble, thus increasing the alignment challenge. Also, thin diameter rods may be too weak and will bend. To enhance the insertion of thicker rods into the accessory case, the insertion end of each may be slightly tapered via a file.

The photo shows the oil screen held temporarily in-place via the two alignment pins (painted white). The use of the alignment pins almost completely eliminates both the alignment problem plus the juggling act of holding the screen housing while inserting the bolts.


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