How do I figure what parts to use for an early O-320?

QUESTION: I have one of the very early O-320s with no suffix. Can you enlighten me as to what modern engine code I should use to buy parts for it? I went to the Lycoming website and it lists the A2A as the earliest generation, but I have heard that is not necessarily correct.

Rick Kelly-Crapse
via email

ANSWER: Rick, thanks for your question. This one comes up from time to time so I think this may be a great place to get it before the public one more time.

The original O-320 that you have was the beginning of Lycoming’s quest to furnish specific models to meet airframe manufacturers’ requirements. Working closely with airframe people, Lycoming found it needed to make subtle changes to adapt to specific airframes. In order to keep things straight, a suffix was added that covered the change from the basic design. I think at one point in time I counted some 50 different configurations of the O-320 engine model series. Your O-320 without any suffix became an O-320-A1A as the series began to expand.

Getting back to your question as to where you need to go to reference parts and other data for your plain old O-320, it is all covered in Special Service Publication (SSP) 488.

This supplement was intended to be used in conjunction with the original Parts Catalog PC-103 for the Standard Flange 320 series engines. It clearly states that for any component you may require for your engine you would now refer to the engine model O-320-A3A.

This covers the previous no suffix and A1A models for everything except the crankshaft assembly and propeller flange bushings. If you should ever need to replace the crankshaft, the information is provided in SSP 488.

Since there are still many of these fine engines in service, I hope this information not only helps you but many others who have scratched their heads over this same question.

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

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