October 2012
Piper Flyer Association member Jim Von Lorenz called the PFA office and asked that I call him. He had read a Q&A column in a previous issue of Piper Flyer and had a question about his engine.
I called a few days later, and the conversation went something like this.
Mrs. Von Lorenz—Joan—answered first and told me that her husband was 79 years old but in very good condition. She said she would pass on my number to her husband when he returned.
An hour later, Von Lorenz called and told me that he was leery of the engine in his 1959 Piper PA-22 Tri-Pacer and he wanted to discuss what he had heard with me.
He volunteered that the engine was a 160 hp Lycoming O-320-B2B that had last been overhauled in 1961, when exhaust valves with the half-inch stems had been installed to comply with AD 63-23-02. A top overhaul was performed on the engine in 1979. The cylinders were chromed using the channel chrome process back to standard bore at that time.
Von Lorenz told me that his mechanic said the engine was in fine shape although he did volunteer that one cylinder was slightly low in compression. I asked how much, and was told it was 62/80; the other three cylinders were all between 68/80 and 72/80.
I asked how much oil was added between changes. (None.) I asked how often the oil was changed and I was told every six months and that it was flown 12 hours during the last six-month period.
Then I asked if there had been any change in the oil pressure readings. Von Lorenz said that there had been “nothing of consequence.”
I then asked if the engine had ever been hard to start. Had it ever run roughly immediately after starting, only to smooth out as it warmed up? I was trying to determine if there had ever been an instance of sticking valves. (This problem usually is first noticed during starting, especially on cold mornings. A common name for this problem is “morning sickness.”)
I was told that it always starts right up and always runs smoothly.
Von Lorenz told me he was leery because he had heard from two different people that he needed to overhaul the engine. When I asked why, he said it was because Lycoming recommends that any of its reciprocating engines be removed for service after 12 years for an overhaul.
Von Lorenz also told me that he had always added AvBlend at each oil change for the last 12 years. He purchased the Tri-Pacer in 1989. He said it was in top-notch shape when he bought it, but admitted that he had only flown about 500 hours since the purchase. The airplane and engine total time were close to 1,900 hours.
I asked Von Lorenz to tell me about his flying experience. He was a retired Navy pilot. “I flew 14 different aircraft over my 21-year career,” he said. I asked which ones. He said he started out flying the Martin PBM Mariner, followed that with the Martin P5M Marlin (an 85,000-pound MTOW twin-engine recip-powered flying boat), then went on to fly the Grumman S2F, the Beechcraft T-34 Mentor and also had a stint in the cockpit of the most glorious C-121 Lockheed Constellation.
I said to myself that Mr. Von Lorenz definitely had a lot of experience flying piston-powered aircraft.
I next asked about a typical flight.
“I usually fly for one to one-and-a-half hours within a 50-mile radius of the private airport in Alabama where I hangar my airplane,” he told me.
“I’m lucky to get four to five hours a month,” Von Lorenz said. “I get a little bit of cross-country on the weekends to see how the neighborhood is doing,” he went on. He added that he sets the power at 2,300 rpm and burns 6.7 to 7 gph.
I concluded that the Von Lorenz’s engine would soldier on for a while longer—that he was in no danger of a catastrophic failure. Here’s how I came to that conclusion.
1. Lycoming Service Instruction 1191A states that “compression readings should be nearly equal; a difference of 5 psi is satisfactory.” If the difference is 10 to 15 psi an investigation should be made. It also states that compressions that are less than 70 psi indicate wear has occurred; that regular compression readings (the bulletin suggests 100-hour intervals between readings) should be taken to determine wear rate. That is already being done at each annual.
2. A common sign of bottom end wear is a slow reduction in cruise oil pressure due to increasing clearances in the main and connecting rod bearings.
In general, the bottom end of all air-cooled GA engines is overbuilt and, if flown regularly, will be dependable for a long time. No change in oil pressure indicates that wear is minimal.
3. A common signal that cylinders and/or valve guides are wearing is increased oil consumption and morning sickness. Since Von Lorenz reported that oil consumption and oil pressure were steady and the engine started and ran smoothly, I wasn’t worried about lower end wear problems or cylinder wear problems.
The primary engine health diagnostic tool is the oil screen or filter. If it shows metal in any appreciable amount, an investigation is indicated. Since Von Lorenz’s mechanic said the engine was in “fine shape,” that told me that the filter was clean.
I did discuss some options if Von Lorenz wasn’t yet convinced, or desired hard evidence. He could pull a cylinder and look inside the engine. Or he could opt to do a top overhaul and either overhaul his existing cylinders, or opt to retire the existing cylinders and replace them with new cylinders from Lycoming, Superior Air Parts or Engine Components, Inc.
One advantage of buying new would be recapturing some of the cost by selling his used cylinders, since the O-320 series of engines is in demand by homebuilders. I also added that the Tri-Pacer would probably attract more attention when it came time to sell if had four new cylinders.
Von Lorenz decided to think about our discussion. In my mind, based on what he told me, Von Lorenz can continue to depend on his engine for the type of flying he does for a while longer.
During a follow up phone call, Von Lorenz said he had been researching the prices of new cylinder kits and was leaning toward replacing the existing cylinders with new ones. He liked the idea that installing a set of new cylinders was the most cost-effective way to both add value to the airplane and insure continued safe engine operation.
Happy Flying.
Know your FAR/AIM and check with your mechanic before starting any work.
Steve Ells has been an A&P/IA for 39 years and is a commercial pilot with Instrument and Multi-Engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as Associate Editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Paso Robles, Calif. with his wife Audrey. Send questions and comments to editor@www.piperflyer.com.
RESOURCES >>>>>
AvBlend Micro-Lubricant
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Engine Components, Inc. (ECI)
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Lycoming
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Superior Air Parts, Inc.
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