Ask Paul: A picture tells the story

Question for Paul McBride, the General Aviation News engines expert: I have a 1960 Piper Comanche. Can you identify the casting number on top of the engine?

And these are Allen bolts holding the crankcase together. When did Lycoming change to newer cap nuts?

JC130Jackson via email

Paul’s Answer: Thanks for submitting this question. The great picture makes it rather easy to answer the question.

If my memory serves me right, the 1960 Piper Comanche used the Lycoming O-540-E4A5 model engine.

So, let’s explain what you describe as the “casting number” on the top rear boss of the crankcase. This is actually the specific engine serial number and it should show something like this: L-XXXX-40. I suspect that the engine serial numbers in 1960 were no more than four digits followed by a number representing the series of that model.

I have circled the areas that you mentioned in order to confirm that we are talking about the same areas of concern.

As an aside, almost all Lycoming engines have the specific engine serial number stamped on the crankcase boss and it should be the same serial number that is stamped on the engine data plate, which is typically attached to the engine oil sump.

With regard to the barrel nuts that retain the cylinders, these were common on all Lycoming engines up until about 1963 when certain models began using what we call the “wide deck” configuration of the crankcase assembly.

Following the introduction of the wide deck configuration, the original cases were then referred to as a “narrow deck” version.

I’d suggest you check out an article I wrote for the Oct. 9, 2009, edition of General Aviation News, “Wide deck vs. narrow deck engines,” which explains the difference between the two versions and why the change was made.

I have recently learned that Lycoming is no longer offering factory remanufactured or factory overhauled replacement narrow deck engines.

I’d like to remind everyone that should it be necessary to contact the factory regarding any engine or submit a question to Ask Paul, please provide the specific engine model and serial number.