Q: I just stumbled onto a post of yours from nearly a dozen years ago, where you were helping identify serial numbers for a gentleman with an Lycoming IO-320 engine.
I am fortunate to get to fly the last airworthy deHavilland Dove in the U.S. As a part of the Riley Turbo 400 Exec mod from the Jack Riley Corp., its Gypsy Queen 70 motors were replaced by IO-720-A1A engines in 1966.
Recently, I tried to get some technical info from Lycoming on one of the motors, only to be told that “the serial number (L-278-54) does not have enough digits.”
Now I am lost, as I pulled the serial number straight off the 1965 data plates, which match the logbooks. I have attached a picture of the #1 engine dataplate.
Am I missing something?
DAN TURNER, Birmingham, Alabama
A: Dan, I give you a tip of the hat for being lucky enough to fly the conversion of the deHavilland Dove using the Lycoming IO-720-A1A series engines. I remember the aircraft quite well and had the pleasure of working on some many years ago.
I’m a bit confused about the factory not being able to provide any information regarding these engines. The serial number you provided is, in fact, a good serial number and definitely does have the correct number of digits.
Normally, the Lycoming serial number sequence for any model begins with serial number 101-XX, so my guess would be that the serial number you mentioned would have been the 153rd IO-720 produced.
The original IO-720 A1A used in the Riley conversion was equipped with Bendix 700 series magnetos, which were a real challenge when trying to time the mag to the engine simply because they used an 8 pole magnet. Finding a neutral position and holding it there while trying to install the mag was frustrating, to say the least. There is no doubt in my mind that many maintenance personnel — including myself — increased their vocabulary while reinstalling the 700 series mags on an IO-720 engine!
At some point the magnetos were changed to the Bendix 1200 series mags, which changed the engine model to an IO-720-A1B. This model change was primarily for the Piper 400 Comanche series, but I don’t recall if this configuration was ever used on the original configuration of 720s used on the Dove.
In answer to your question, no, you are not missing something. I hope the little history lesson mentioned above will give you some background.
In my opinion, the Lycoming IO-720 was one heck of an engine and to my knowledge is still in current production. Many of this 720 series engines were used on crop spraying aircraft built by Piper (PA-36 Brave), Pacific Aerospace Fletcher (FU-24) in New Zealand, and the Transavia Skyfarmer (T-400) from Australia, among others in India, Brazil, and China. They were also used in several other conversions over the years.
