Air-Oil Separator installation on a Swift

From: Miguel Nelson" <>
Yo Denis,
Happy 4th of July! I thought I would give a detailed debrief to any interested parties about the installation of the M-20 Air/Oil Separator on the Continental IO-360C and the results after flying my Swift for about 4 hours worth on the holiday weekend.

First I must say that I was initially disappointed with STC kit itself. For $260 (without tax) you get the air/oil separator, the STC paperwork and some very basic, if not crude, installation instructions. Absolutely no hardware is provided (hoses, fittings, clamps, etc.). I understand that this air/oil separator is approved on a large number of engines, but the manufacturer should (in my opinion) provide at least basic hardware for the particular engine installation. Having said that, there is not that much hardware required, it would just be nice considering the amount of money being spent. The instructions talk about the oil return line being connected to a welded y-joint to a cylinder oil return line (not an issue for Continentals), welding a 1/4" line on the rocker cover of the rear cylinder, a hose barb through a rocker cover, or drilling a hole in a rocker cover and using an AN type elbow fitting if an unused plug cannot be found crankcase. Again, an assortment of included hardware would have been nice. Here is how my installation went.

The first problem is that air/oil separator is approximately 8 inches long and must be mounted vertically for gravity flow draining of the 1/4" oil return line. This leaves very few options for mounting the separator even if you were to try to use a rear cylinder rocker cover for the return line. Compounding the problem is the fact that the Swift is a taildragger, so the separator must be mounted even higher for the bottom 1/4" return line to be higher than the cylinder rocker cover. You are of course limited by how high you can mount it due to the cowling. I looked everywhere on the crankcase for an unused "low pressure" plug, and could only find two. One was on top of the crankcase (too high) and one next to the oil screen (high pressure). I had pretty much given up and was going to return the separator, since I refused to drill a hole in a rocker cover, and I wasn't even sure if it would be low enough. This thing had been advertised as being an easy installation and it was fast getting into the "too hard category" for me. I called Gerry Hampton and told him the difficulties I was running into. Gerry had planned on purchasing one and installing it, so I offered to sell him mine, otherwise I was returning it to Spruce. He stated that based on what I had told him, it would probably be to hard for him also. The next morning, just previously to me boxing up the separator, Gerry called an said that Kurt Von Salzen had told him that there was a low pressure plug just above the tach drive pad. I went and looked but could not see one. The IO-360C's have that T on the accessory case for the starter and vacuum pump and there is little room between that, the mags, tach drive, and alternator. Kurt insisted that there was one, and after getting a flashlight & inspection mirror, I found it. Kurt also informed me that the plug was originally intended for an oil return for a wet vacuum pump. This changed everything, although I might add the plug was very difficult to reach. Kurt had suggested removing the left mag and my roommate had suggested removing the vacuum pump. But since I am stubborn and refused to complicate the installation any more than necessary, it took me two hours to get the plug out. It was a 7/16" square plug with a 3/8" pipe thread. A square plug socket or a six point socket will do the trick, but there is little room to maneuver. No room for a crow foot or wrench. I was able to find a brass fitting that went from a 3/8" pipe thread to a 1/4" barbed line at Ace Hardware, eliminating the need to use a reducer from 3/8" to 5/16", which is more common for a 1/4" line. I cut a 1 inch diameter hole approximately 1 inch below the top of the left rear baffle. I mounted the separator so that the bottom 3/4" line would just clear the left mag. The separator was mounted to the aft side of the left rear baffle using one large adel clamp with the top 3/4" line going through the 1 inch hole and connecting to the crankcase vent tube which had been cut to length. I then mounted a cover on the previous existing hole in the baffle which was approximately 6 inches below the new one. I then simply connected about 10" of flexible 1/4" hose from the return exit on the separator to the new brass fitting with the 1/4" barbed line, which is about three inches below the separator. Hardware required: (2) 1-inch hose clamps, (1) 1/2-inch hose clamp (none require on barbed line), (1) brass male fitting (3/8" pipe thread to 1/4" barbed line), 1 foot of flexible 1/4" line, (1) large adel clamp for 2" diameter separator. I ended up with just enough 3/4" hose since I cut it to length to connect to the top of the separator where the hole in the baffle had been moved up about 6 inches and the piece I had left just made it to the bottom of the firewall. And now the operational results.

My engine has never thrown a tremendous amount of oil, but after flying it for a few hours, I would always have to wipe some residual oil of the belly. I might also add that my engine typically stabilizes at about 8 quarts and I never service it with more than 9 quarts (i.e. oil changes). The manufacturer of the air/oil separator states that you can now top off you oil without throwing 1 quart or more out the vent. Although I am usually an optimist, I was wondering if this $300 investment was going to make any noticeable difference. Since I just completed my annual inspection along with the separator installation, I serviced my engine with 10 quarts for the first time. I spent the holiday weekend at Sea Ranch, CA. I flew my Swift from Cameron Park to Sea Ranch, Little River, Ocean Ridge, and back to Cameron Park, along with some aerobatics of course. After approximately 4 1/2 hours of flying, I still have 10 quarts of oil and absolutely none on the belly! It really does work as advertised! It was definitely a worthwhile investment and I hope others will benefit from the information provided. Check six, Ozzie