Question for Paul McBride, the General Aviation News engines expert: I am looking at pre-oiling Lycoming engines, such as the O-320-E3D, O-320-E2D, D2J, etc., installed in Piper Warriors and Cessna 172s.
I was planning on removing the oil line coming out of the engine going into the oil cooler, installing a fitting, and pre-oiling with about 25 to 35 psi through the oil cooler. While camping the fitting on the engine, this should flow the oil cooler and the rest of the engine, bypassing the Vernatherm and back flow into the filter and oil pump.
Originally, I was looking at tapping into the center post of the oil filter adapter, but this would not let oil flow through the oil cooler, which for a fresh engine would not be a problem, but for an engine that has been sitting, it would be good to flush out the oil cooler at the same time.
What are your thoughts?
Glenn Ingle
Answer from Paul McBride: Glenn, the first question I’d have to ask is what you are attempting to do?
If you’re thinking is to lubricate the entire internal components of the engine, I hate to tell you that it’s not going to work.
Sorry for being so blunt, but pre-oiling Lycoming engines with, let’s say 25 to 30 psi from an external source, would only pre-oil the main, connecting rod, and cam bearings, or any area that is serviced by a direct oil pressure point.
If your thought is to pre-oil the cam and tappet faces by using this procedure, it’s not going to work. The cam and tappet areas are only oiled by splash oil and have no direct pressure oil points.
While this design has been questioned over many years, it is what it is and has served Lycoming engines relativity well since the 1930s when the first flat opposed Lycoming was certified.
Please don’t confuse my statement with this being a perfect design, but in most all situations, it has worked fine.
We all know of some situations in the past where cam and tappet spalling was a problem on certain engine models. The problems were addressed on those specific engine models and engineering redesign corrected the issues.
Again, my guess is that you want to eliminate any possibility of internal lack of lubrication during engine start-up.
As I mentioned previously, since the cam and tappet area are only served by splash oil, if you really want to focus on that area and keeping it in the best of health, here are a few suggestions.
First, the worst thing that you can do for an engine is allow it to have extended periods of inactivity. Couple that with infrequent oil and filter changes, and you’ve opened the barn door for internal engine corrosion, especially in the area of the cam and tappet interface.
If you can picture the tappet body face being a vertical surface and can imagine what happens to the oil on that surface as time passes when the engine is sitting inactive, the natural occurrence is that the oil drains off of the surface.
What has a tendency to remain are the by-products of combustion and they are acidic in nature. These remnants of what was once a lubricated service are now contaminated and the corrosion process begins. The process is aggravated by extended periods of inactivity, as you can imagine.
On the next engine start-up when the cam lobe swipes across the face of the tappet, metal is displaced, and the spalling process begins. Unfortunately, that condition will never get any better and will, over time, continue to displace metal. At some point, you’ll become aware of this when you cut the oil filter open for inspection during a routine oil and filter change.
If you operate these engines frequently and change the oil and filter frequently, you shouldn’t have to worry about pre-oiling. I’d also suggest you read the latest version of Lycoming Service Bulletin 480.
If it’s a question regarding the aircraft not being flown during the winter months, the best thing to do is change the oil and filter before storing the aircraft for any period of time so those acidic properties in the engine oil don’t get a chance to begin the corrosion process.
Also, do not turn the prop and put a sign on the prop stating that. That’s always a good idea.
I hope I’ve addressed your question and hopefully given you some insight as to how to deal with this type of situation.
