Ask Paul: What is proper timing for my engine?

Q: I am an Italian homebuilder of a Van’s RV-3. I read on the Internet that you are an expert of Lycoming and I want to impose on your kindness. I am ready to make the timing on my Lycoming O-290 D2 but there is a little doubt about the timing degrees because the O-290 is not a common engine in Italy, as it was used only by the Italian Army in a PA18. An AD issued in 1954 changed the timing at 18° (label on engine) to prevent detonation, probably with 80/87 fuel. If I use 100LL, will I have to change the timing? Many thanks in advance and sorry for my bad English.


A: The question regarding the proper spark timing on the O-290-D2 model engine has caused some confusion over the years. I referred to the O-290 Operator’s Manual Part Number 60297-9 and it tells us the correct timing for your O-290-D2 is 18° BTC. The other O-290 series engines are timed at 25° BTC. Regardless of the fuel used, 100LL or the old 80/87, the O-290-D2 should be timed at 18° BTC.

I’d recommend you consider purchasing a Lycoming Operator’s Manual for your engine because it will provide you with much information that will be useful as you operate your engine in your Van’s RV3. Since good knowledge may be difficult to find in Italy, may I recommend you contact the nearest Lycoming Distributor, which is O.A.D. Officine Aeronautiche David, Via Galileo Galilei, in

Brescia. Phone number is (39) 030-2667133; the website is I have traveled to their facility and can tell you it is an excellent facility with an outstanding staff of knowledgeable technicians.

I wish you good luck with your RV-3 project and thank you for your question. Also, Piero, you do not have to apologize for your bad English, because it’s much better than my Italian!

Paul McBride, an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:

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