Flying Club has a Cessna 172-F with O-300-D engine.  Started oil change but could not locate the filter screen.  Did find one on the lower left of accessory case but it has no screen, just a 'barrel' with 3/16" diameter holes.  I helped with an oil change on the plane several years ago and recall removing only one filter screen. Wonder if I have the right barrell and someone forgot to replace the fine screen after cleaning it . . . ?

Thinking of adding an F&M CO-300 adapter and wonder if it mounts where the barrel I removed was or if there's another location.  Read somewhere on this forum that the barrel I removed is on the 'suction' side and that the filter screen is on the 'pressure' side and is at the 2 oclock position on the case.  Only thing in that area on ours is the tachometer drive.  If there is a fine filter screen I assume it has to be removed when installing a filter adapter and wonder if it matters if the adapter is on the suction side or pressure side?