Paul McBride, an expert on engines, retired after almost 40 years with Lycoming.
Q: Hi, I am a Mexican looking for my first plane. I found a 1980 Cessna 172 with an H2AD engine that has just 100 hours since overhaul. The serial number ends in 76T; I had read about 76A. Is it OK? Is it the same as the 76A?
GERARDO ARRIOLA, via e-mail
A: Hola Gerardo. Thank you for your question regarding your possible purchase of a 1980 Cessna 172 with the Lycoming O-320-H2AD engine. The information you provided was enough to tell me the engine is of the latest configuration like those engines currently being shipped from the Lycoming factory as replacement engines for this aircraft.
The suffix to the engine serial number is the defining factor and since you mentioned this engine serial number suffix ends with -76T it confirms this engine contains all of the upgrades Lycoming made to this engine model, which includes a wider lobe camshaft and the largest diameter tappet bodies. These product improvements were the key to improving the reliability of the O-320-H2AD engine. The “A” suffix you mentioned does not apply to the O-320-H2AD engine model.
Just as a precaution, before you purchase this aircraft I’d review the engine logbooks for the engine’s history. You mentioned the engine has 100 hours on it since overhaul and I’d be curious to know how many calendar months it took to get this 100 hours. My concern is extended periods of inactivity, which may allow internal corrosion to begin. If there has been extended periods of inactivity, I’d recommend having a good maintenance facility remove one or two of the tappet bodies, allowing for a good visual inspection of the tappet face and the corresponding camshaft lobe for any indication of corrosion. As a suggestion, I’d remove the #1 and #2 intake tappets since they share a common camshaft lobe, which should give you a better perspective of any problems occurring from corrosion inside the engine.
We at General Aviation News wish you well should you find this to be the aircraft for you, and hope you enjoy many happy flying hours.
Send your questions to: AskPaul@GeneralAviationNews.com.