What are the best options for overhaul?

Q: My question seeks your advice about an overhaul on our Lycoming O-320-H2AD. As background, we have a 1980 C172N that’s been owned since new. It’s always been hangared, never been a flying club or training airplane, is not used for commercial purposes, and has 2,420 TTAFE tach time.

The engine is the original H2AD and it has not been topped. It runs smooth, develops good power, and the airplane performance matches book figures. We change the oil (Phillips X/C 20W50) and filter regularly and use the Lycoming oil additive. Its oil usage is 1 quart every 9-10 hours and there’s no oil on the belly or visible smoke from the exhaust. The cylinder compressions hot were 70-74-74-76 just last month and the exhaust system is in excellent condition with no leaks. The plugs show no evidence of oil deposits and only light carbon deposits, which clean easily. During run-up, the Bendix D2000 mag shows a drop of 50-60 rpm on both sides with little differential.

We usually start the engine when surface temperatures are above 34° and rarely fly it in colder weather. We will forgo the flight or preheat it if the weather is cold and we still need to go. For the past two years we’ve averaged 40 hours a year, with most of those hours being 60-90 minute flights, including practice landings, about every 15-20 days. In 2013 we intend to fly it at least 60 hours with more flights of at least two hours cruise duration.

While the engine is remarkably reliable, given the total engine time alone, we’ve been discussing how best to approach the inevitable overhaul. The three options seem to be: 1) wait until it begins to show signs that it’s ready to have something done (i.e., if it ain’t broke, don’t fix it); 2) keep the bottom end as is and replace the top end with overhauled or new cylinder assemblies); or 3) perform a major overhaul and replace the camshaft, lifters, bearings, and anything else that appears necessary. Regardless of which we choose, we plan to upgrade the Bendix mag to a D3000 configuration at the same time.

What’s an early indicator that it’s “time” to do something?

Cost is a factor, but it’s not a show-stopper. We’ll do what’s necessary, but with other needs, such as avionics replacement, we’d like to do the smart thing well. My inclination is to not replace our first run H2AD engine, as our airplane is much smoother and seems to outperform those who I know have switched to other versions of the O-320.

KEN PEPPARD, via email

A: I must say I found your email very interesting and I’ll see what I can do to pass along some thoughts that I hope will assist you in making your decision when the time comes.

First of all, I must compliment you on the details you provided regarding your O-320-H2AD engine in your Cessna 172N. As I’m sure you know, there are many folks in our industry who have heard all the bad things about the Lycoming O-320-H2AD engine over the years, and I personally lived through a period in time where the reputation of this engine was, shall we say, less than stellar. However, there are many operators of this engine who have successfully completed operational hours similar to you and, in some cases, even more.

When I review the information you provided regarding the operation and maintenance of your engine, I can’t help but hope that all of our readers would take a lesson from this. Ken, you are doing exactly what every aircraft owner/operator should strive to do. You’ve proven that maintaining and operating an aircraft in this manner has its rewards by continuing to provide reliable, safe flying.

Let me address the three options you detailed in your email. 1) I can’t tell you how much more time you may get out of this engine. That being said, I can tell you from experience that an engine just doesn’t up and fail without some warning indications. Some of these signs include an increase in oil consumption, hot differential compression checks with lower readings, or signs of contamination in the oil filter or screens, to name a few. With the detailed information you provided, I know you would notice any changes and further investigate why something has changed.

I’d like to add something here that I hope other owners will take note of and that is the importance of keeping detailed records on everything about the aircraft. It’s vital to the operation of a safe and reliable aircraft to maintain these records for reference, especially as the aircraft ages and/or approaches high time. Probably the two most important things to record over the life of the engine is the oil consumption and the hot differential compression checks. Also, cylinder head temperature and oil temperature over the life of the engine could provide valuable information. Having oil analysis over the life of the engine is also a great tool when it comes to knowing just what is happening inside your engine.

Back to your options. I must vote against option number 2. Keeping the bottom end at this point in your engine’s life would be like running a marathon, taking a shower, then putting the same clothes you ran the marathon in back on and going out to a restaurant for dinner. You might feel better after the shower, but the clothes would still stink!

What I’m saying is, the total time on the engine would continue in the logbook and some of the major components that may have needed or required replacement will go uninspected, leaving lots of questions as to the reliability of continued operation.

Option number 3 is more to my liking, but I think I can recommend even a better option to you. While your engine can certainly be overhauled in the field by one of several reputable FAA approved engine overhaul facilities, I don’t think it’s the best way for several reasons. First, the O-320-H2AD has gone through several improvements, which your engine does not have. Remember, your engine is the original configuration of the “H” engine (L-6644-76 shipped from Lycoming May 30, 1979, for installation in your 1980 year model aircraft) and the first major product improvement came about in April 1980 when Lycoming went to a wider lobe camshaft and a larger diameter tappet body. Other product improvements have been introduced over time and are all items that have added greater reliability to this engine. You mentioned that you still have the Bendix D-2000 series magneto on your engine and this is another item, as you know, that has been improved and the D-3000 mag is now in current production and would now be installed on your engine.

At this time, you can exchange your original configuration O-320-H2AD engine through any Lycoming distributor of your choice for a Factory Rebuilt Zero Time New Logbook at list price for around $31,500. Now, before you fall over, this means you get a Zero Time Logbook, but more importantly, all of the latest factory upgrades and product improvements, such as a new camshaft, new hardened steel tappets which use the same material as the tappets used in the Lycoming HIO-360-D series helicopter engine that is rated at 3,200 rpm, which certainly says something for the material durability. And, the D-3000 magneto would be standard.

It’s no secret that approaching your situation with this option will definitely increase the value of your aircraft — my best guess would be at least 15% to 20%. Just for kicks, why not make a few phone calls to aircraft appraisal facilities and inquire? There is also a factory overhaul engine available on an exchange basis.

I know you are aware that there are other engine options and conversions available for the Cessna 172N series aircraft. One of them is to convert to the Lycoming O-320-D2J 160-hp engine or the O-360-A4M 180-hp engine. These conversions have been very successful over the years and many of the upgraded conversion to the O-360 180-hp engine seem to be quite popular. I believe the reason behind this is the old saying “people buy horsepower.”

However, this may not be the case for you and there is certainly nothing wrong with that. As you know, even with the increase in horsepower, there is no such thing as a free lunch. Yes, gross weight will probably increase some, and you can expect a little more speed along with better climb performance, but there are other factors that might influence your decision of going this way. We all are very conscious of fuel costs these days and with the 180-hp conversion, your fuel consumption will increase roughly from 8 gph to 10 gph or about 25% higher. While certainly not a show stopper, it is something that deserves consideration.

Just as an aside, from my past experience with regard to conversions, I believe that Air Plains in Wellington, Kansas, has probably completed the most engine conversions on the Cessna 172. Having completed more than 2,600 conversions on the 172 certainly speaks to the popularity of program. There are also other STC holders doing conversions and a little research on your part will answer who makes these conversions available.

I’d like to mention one more thing concerning the Bendix Dual Magneto, regardless of the series. This is a product that has sometimes gotten a less than desirable reputation for various reasons, such as “it only has one gear driving it.” Well, friends, an engine with two individual magnetos only has one crankshaft gear driving both of them. There is one thing I can tell you for sure with regard to the dual magneto and that is…if you maintain it in accordance with the manufacturer’s recommendations, it will serve you well.

One of the biggest problems over the years is the fact that many maintenance facilities and technicians were not familiar with the product nor knowledgeable enough to properly maintain it, resulting in mag failures and the unit getting a bad reputation.

Well Ken, I’ve certainly covered a lot of ground here from your great questions and I can only hope it will be of some help as the time approaches for you to make the “big decision.” There is no doubt in my mind that you have the experience and knowledge to research and digest all of the important information that goes into this difficult decision and you’ll end up doing the best thing for you and your aircraft.

I sincerely hope that others who take time to read this column will adapt some, if not all, of the things Ken mentioned in his email and also those I pointed out regarding record keeping of vital information. While it may seem to be a bother to do this over the life of the engine, I strongly believe you’ll feel better knowing exactly what your engine is doing and it may alert you of any changes in the health of your engine.