What parts can I use in my 1955 engine?

My 1955 Tri-Pacer original Lycoming O-320 engine was torn down and inspected. It has a Part No. 74166 camshaft gone bad (#3). I found a P/N 76097 camshaft. Is it OK to use this part number for the engine?


Broken Arrow, Oklahoma

Wendell, to answer your question, no, you cannot use the P/N 76097 camshaft as a direct replacement for the P/N 74166, but don’t leave me just yet. It looks like you’ve got a real challenge on your hands with your model O-320 (no suffix) Lycoming in your 1955 Piper Tri-Pacer.

If I were to guess, it sounds to me like this must be the original engine since it has just a plain O-320 with no suffix in it. Now that you’ve discovered the camshaft is no longer serviceable you’ve got some work to do. First, the camshaft assembly part number used in that engine originally was P/N 74167, which was made from a camshaft P/N 74166. When the dowel for the cam gear was installed, it became a P/N 74167 camshaft assembly. Unfortunately the P/N 74167 camshaft assembly has been out of production for many years. This was brought on by a product design change way back in the late 1970s or early ’80s that incorporated a completely different camshaft assembly and accessory housing in addition to other associated parts. This change utilized a one piece camshaft assembly and a different accessory housing that was compatible with the new camshaft assembly.

So where does this leave you, Wendell? Well, you’ve got a couple of choices available as I see it. You can try to locate a good used serviceable P/N 74167 camshaft assembly. That would be the easiest and probably the least costly. The big problem with this, I’m afraid, is that this part number camshaft assembly may be difficult to locate, but you won’t know until you try.

The other option is to comply with Lycoming Service Instruction 1218A dated Oct. 1, 1982. This publication provides all of the information required to make the change by listing the old part numbers and what is to be used with the new configuration. As some of the good old boys would say, “”this ain’t gonna be cheap”” and they’re probably right.

My best recommendation is to contact a reputable engine overhaul facility and sit down with them to see what you can come up with. If you are lucky enough to locate a P/N 74167 camshaft assembly, you’re in good shape. If you can’t, then the cost goes up, but have them take a close look at Service Instruction 1218A to see if they might be able to offer any other options, like locating some used serviceable “”Yellow Tagged”” parts that could be used with either what you’ve already got or to make the change spelled out in the Service Instruction.

This is not an insurmountable challenge, but does test one’s patience — and in some instances people’s vocabularies increase with words that may not be too nice.

Good luck Wendell. I’m sure things will work out for you.

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

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