Question for Paul McBride, the General Aviation News engine expert: In your recent column, “The fall-out from not doing due diligence,” you mentioned narrow deck and wide deck engines. My question: “Is a narrow deck an angle valve 540 and a wide deck a parallel valve 540? “
Thank you.
Robert
Paul’s Answer
Robert, if you only knew how tempting it was for me to just respond to your question by saying “yes,” but that wouldn’t do anything but decrease your frustration, and I’m the last person who would want to do that during the holiday season.
So, the true answer is that a Lycoming O-540 series engine can either be a narrow deck or a wide deck, and it has nothing to do with parallel or angle valve configurations. If we use the O-540/IO-540 series, the earlier models, depending on horsepower, could either be parallel or angle valve.
Probably the easiest way to determine what you have is checking the engine serial number. The narrow deck engine serial number will be something like L-XXXX-40, while the wide deck version would have a serial number something like this: L-XXXX-40A.
Another way is by looking at the engine and noting what type of nuts are holding the cylinder to the crankcase. The narrow deck engine uses an internal spline barrel type nut, whereas the wide deck uses regular type hex nuts.
I also should note that narrow deck and wide deck cylinders are not interchangeable.
I hope this simple explanation will get things straightened out in your mind, and I appreciate you asking this question because I know it’s confusing.
I’d think the most useful starting part of the answer would be a definition of the deck? What constitutes a wide or narrow deck?
do google search for …wide deck vs narrow deck Lycoming engines
It has to do with the cylinder base mounting flange thickness and strength.
Very helpful in understanding how to identify narrow versus wide deck designs. Would be helpful to understand the substantive engine differences, pros and cos.