Ask Paul: Tips to getting Dad’s Pacer flying again

Q: I was reading your explanation on the difference between narrow deck and wide deck Lycomings — what an excellent piece of writing. My interest is that my brother Lee and I have my Dad’s PA-20 and, while stored indoors, it hasn’t flown since 1964 or so, but I’m thinking (perhaps foolishly) about putting it back together. I’m thinking the old O-290-D-2 (while in excellent shape and only 200 TT, but 7/16ths valves) will have to go. An O-320 is approved in the Wag Aero and Copper River STCs for the PA-20 (so is a 160 by another company). I don’t know why the O-320 works out so well in the Pacers, it’s only another 15 hp.

The big question is that I have found several narrow deck O-320s for sale and wondered if that engine is any more or less worthwhile than the wide deck version. There’s lots of rumors, but no facts.


 A: Al, it looks to me like you’ve got a real gem in the rough and I’d like to encourage you and your brother to turn the flame up on getting your Dad’s PA-20 out of storage and getting to work on its restoration.

As far as the engine to be used, I guess it all depends how much money you want to spend and how quickly you want to get your Dad’s plane flying again. That being said, if the O-290-D2 presently installed only has a total time of 200 hours, I think that may still be a viable choice. However, if it were mine, I’d probably do a little investigation work first before firing it up and flying off.

With regard to the exhaust valves presently installed in the engine, there is nothing that requires you to replace them. I would suggest that you review the contents of a couple of important Lycoming Service Instructions. The first is Lycoming Service Instruction 1070Q dated July 16, 2010, which covers the subject of “Specified Fuels.” This information should be read and digested and then I’d suggest you read Lycoming Service Letter L185B, which discusses “The Use of Higher Octane Aviation Fuels” in engines rated for 80/87 octane fuel. You may gain enough knowledge from these publications that will assure you that operating the engine in its current configuration is OK, and other than the guidelines and inspections called for in those publications, all is well as is.

You may prefer to go a different direction and comply with Lycoming Service Instruction 1246A, which covers the “Engine Conversion For Use of 100/130 or 100LL Fuel.” This may be cost prohibitive for you at this point, but it is something to consider. Complying with this publication will eliminate the inspections called for in Service Instruction 1070Q.

Before jumping into a conversion, you may want to run the numbers on the upgrade to an O-320 engine, as you mentioned. There is nothing wrong with an older model that uses narrow deck cylinders. Should you ever encounter a problem with this type of cylinder, Lycoming continues to supply new narrow deck cylinders. It does not supply narrow deck crankcases any longer, so if your crankcase should develop a crack that required it to be replaced, you would have to locate a used serviceable case from a source other than Lycoming. There is no doubt that the number of these cases will decline as the years pass, so that in itself may be a good reason to consider spending a little more money now and going with a newer wide deck engine. The front main bearings are the same whether it’s a narrow deck or wide deck. The front main bearing is only different on the O-320-E2D and subsequent models. Remember, if you should find a 320 series, it must be a “conical mount” and not a “dynafocal” type mount.

Getting back to “if it were mine:” I’d probably do a bulk strip of the engine by removing all of the cylinders and giving them a good thorough detailed inspection. I’d look for any signs of corrosion, checking the dimensions of all the components, and just do a good general visual inspection. I would also do a good inspection of the cam and tappet area using a light and an inspection mirror and be on the lookout for any signs of corrosion. If no corrosion is seen, I’d say you’re in pretty good shape and would consider putting the engine back together.

As good shop practice would dictate, the cylinder barrels should be honed and new piston rings installed. Some people might ask with only 200 hours on the engine, why hone the cylinders and install new rings? The reason is that once you disturb the marriage between the cylinder wall and the rings once they’ve seated, you cannot assume you’ll have the same compatibility. The risk is you may end up with a high oil consumption problem. If that happens, the only cure is to remove the cylinders and hone them and install new rings, so why take that chance? If you do it right the first time it will prove to be a money saver for you compared to doing it over because you thought you could save some money the first time through.

Also, as you mentioned, there are a couple of FAA STCs out there that you may want to consider. If you decide to pursue this, I’d suggest you talk with the STC holder or someone who has completed the conversion to get all of the facts. There is no doubt that an additional 15 horsepower would improve aircraft performance, but the question remains: Do you really need it when you balance the improvement in performance for how you’ll use the aircraft versus the cost? Remember, you have to pay for horsepower.

Al, I hope I’ve helped dispel some of the rumors and offered you a few facts, as I see them, and I wish you well with your project. I will say one more thing: Whatever you decide, please get your Dad’s airplane back flying again because I know it will mean so much to you and your brother.

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


  1. Kent Misegades says

    We have a similar O-290-G/D GPU conversion engine in our Stits Skycoupe we’re
    restoring, and I believe that we have retraced the history of these
    once-popular engines from the early homebuilding movement.  Most of
    these engines were sold to the public with only a few hundred hours
    of use in well-maintained military ground power units.  The
    conversion to a -D model consisted mostly of adding a second
    magneto/harness/plugs, a split strengthening plate (designed by
    homebuilding icon John Thorp) on the relatively thin prop flange,
    and a new airbox.  On our engine we swapped the ancient Scintilla
    mags for a near-new set and obtained a near-new M-S
    updraft carburetor.  The engine as we acquired it already had a
    larger oil sump from an O-320 installed.

    You may know that the O-290-G/D powered Dick VanGrunsven’s first
    RV-3, as well as many other aircraft in the 60s and 70s.  While Dick
    was known to have flown some impressive aerobatic routines in this
    plane, we would advise against this given the relative strength of
    the crankshaft and prop flange compared to engines use for serious

    When these modifications are made, and the engine is operated
    correctly, it can be a reliable and inexpensive alternative to other
    engines.  Its one major drawback is lack of some critical
    replacement parts.   Since one can find these engines though at
    very low cost, it makes sense to run them until TBO or when they
    need new parts and then replace them with a more
    common engine like the O-320.   The EAA put out an entire manual
    on converting the engine from the -G to the -D model. We have a
    copy, but I do not know if it is still in print.

    This Lycoming document might also be of use:

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