My 1967 Cessna 172H has the old oil filter screen instead of an oil filter. I had changed the oil a couple of times without having removed, inspected and cleaned the oil filter screen, so with this oil change, I was going to make sure and clean the screen as well. It was overdue. As with everything else about the airplane, this was going to be a learning experience.
With the cowling off, I drained the oil as usually from the quick drain. I let it drain for a good while to let as much as possible come out of the quick drain to avoid having so much come out when removing the oil filter screen. I snipped the safety wires from the oil screen and unused sensor plug bolt head which is bolted into the head of the oil filter screen. Next I loosened the oil filter screen with the torque wrench, a three-inch extension and a one inch crowfoot wrench. I did not loosen or remove the smaller hex-head plug bolt on the end of oil filter screen.
I carefully backed the oil filter screen out by hand just enough to allow oil from the sump to drip into a plastic cup that I had wedged in underneath the filter screen to catch the oil. I happened to use a clear plastic drink bottle that I happened to have handy. I cut it in half and used the bottom portion. It helped that it was clear so I could tell if the cup might overflow. About a cup and a half of oil came out so I did have to hand tighten the screen back to stop the oil flow and dump the cup out and then go back and loosen the screen again and get the remaining oil out. Once the dripping stopped, I carefully removed the oil filter screen from the crankcase and noted which way the old copper crush gasket was installed; the open “parting line” was facing the crankcase.
I inspected the oil filter screen for any debris such as metal flakes. Then I cleaned the oil filter screen in some avgas and inspected to ensure it was in good shape. It looked just fine.
Back at the crankcase opening, I put my finger in just inside at the bottom to “scoop” out as much oil as I could onto a paper towel underneath to stop any dripping, then cleaned the outer surface where the oil filter screen and crush gasket come in contact with the crankcase.
I inspected the opening in the crankcase with an inspection mirror, shining a flashlight onto the area so I could see well. Everything looked fine with no mars or other abnormalities.
I checked to make sure the oil quick drain was closed and then reinstalled the oil filter screen. I placed a new AN900-28 [MS35769-48] with the “parting line” facing the crankcase. I am not sure how to interpret the SB that says to install the copper crush gasket with “the parting line up against screen face.” Not sure what the “screen face” part means so I just put the new copper gasket in the way the old one was installed before –
I was careful to make certain the that copper crush gasket was centered well when hand tightening the oil filter screen. It is a little loose and can move up, down or sideways slightly. If need by, you can put a little bit of grease on the face of the oil filter screen where it contacts the crush gasket to ensure that it stays centered in reinstalling the oil filter screen into the crankcase. I did not have to use any grease, but made sure it was centered by holding the copper crush gasket in place with three or four fingers around the head of the oil filter screen assembly while screwing it back into the crankcase to hand tight.
Once the oil filter screen was hand-tightened with the copper crush gasket centered in place, I tightened the oil filter screen with the torque wrench set at 42 ft#. This required a little finesse as that is a bunch of torque and the crowfoot wrench tends to want to slip off. You have to hold it in place with one hand and torque with the other.
Once the oil filter screen was reinstalled, I filled the engine with oil (I use seven quarts, but cause this engine will blow out the eighth one pretty quickly.) After a few minutes, I checked the oil filter screen to see if there was any oil leaking. It looked clean so I pulled the airplane out of the hangar and started the engine, did a run up and then a full static run up, shut it down and inspected for leaks around the oil filter screen once again. There was no oil leaking, so I went flying!
Tools:
5-80 foot pound (ft#) torque wrench
3”
1” crowfoot wrench
Needle nose pliers
Wire cutters
Safety wire tool
Flashlight
Inspection mirror
Supplies:
AN900-28 (1.75”) [new part number MS35769-48] copper crush gasket (I bought several from Aircraftspruce.com but your local A&P should have some)
.041 safety wire
Clear plastic cup
Paper towels
Note: Continent SB76-7C, page 7, calls for a 1.75” copper crush gasket [AN900-28], and tightening to 500-520 inch pounds (in#) or 41.6-43.3 ft#, and says to install the copper crush gasket with “the parting line up against screen face.”
See the SB online at: http://www.tcmlink.com/pdf2/SB96-7C.pdf