Can I install a constant-speed prop on my engine!

I have a Lycoming O-360-A3A in my Cherokee. According to the Type Certificate Data Sheets (TCDS), this engine is similar to an -A1A, except without provisions for a constant speed prop. Nevertheless, it is equipped with a hollow crankshaft, and there is a pad on the accessory case for a prop governor.

A friend told me this engine will accept a constant speed prop with the removal of the front crankshaft plug and installation of the prop, governor and associated hardware (effectively converting it to a -A1A). I have looked online and at the FAA database for an STC to do this, but didn’t find anything.

Is my friend right? Can I install a constant-speed prop on this engine?



Wade, you’ve presented a question that has me scratching my head. It’s not that the question is difficult, but rather it’s one that has me confused just a bit. Maybe I’ll begin to answer your question by asking a couple of questions first: Are you positive that you really have an O-360-A3A in your Piper Cherokee? Which model Cherokee do you have?

The reason for my question is after researching the information I’ve got access to, it does not list this model for the 180 Cherokee. We know that the Cherokee D utilized the Lycoming O-360-A4A, which is the same as the O-360-A3A except the A4A has a solid crankshaft and cannot be converted to a constant speed prop configuration. The Cherokee C model used the Lycoming O-360-A2D.

As far as the engine is concerned, “”if”” it’s got a hollow crankshaft it should be convertible to a constant speed configuration in accordance with Lycoming Service Instruction 1435. Please keep in mind the fact that it may be done in accordance with approved data from Lycoming, but it may not meet the requirements of the Type Certificate of the aircraft and that’s where the STC comes into play. Like you, I couldn’t locate an STC to cover the installation of the O-360-A3A in any Cherokee series aircraft, but that’s not to say there isn’t one out there and you and I just didn’t look in the right places. Maybe a more knowledgeable reader will be able to provide this information to us.

One other approach you may consider if, in fact, there is not an STC out there would be to consider getting the conversion approved under an FAA Form 337. I strongly recommend you discuss this with the maintenance facility that would be doing the actual work and its FAA FSDO office or its principal maintenance inspector before putting any money on the table.

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


  1. John Galban says

    Just an FYI. I found this old article via a Google search while looking for something else. I just wanted to point out that the Cherokee 180s prior to the D model (’68) did in fact use the O-360-A3A as Wade Sullivan mentioned. If you check TCDS 2a13, you’ll see that the -A3A and solid crank -A4A were the only engines used on the Cherokee 180.

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