Rear Cockpit

Advice on advice.


Advice, it is said, is worth what you pay for it. Ultimately this is mainly true, and there are few better places to test the theory than at the airport.

That’s because there are many (mainly) intelligent people fiddling with airplanes they don’t completely understand—which, when you get down to it for most of us, is true of just about any device more complicated than a #2 pencil. And that’s because well-adjusted, mainly intelligent people are typically mentally engaged elsewhere and often find better ways to spend their lives than memorizing AC 43.13-1B. Certainly they don’t fall asleep each night while imagining themselves as an oxygen molecule flying down a Lycoming intake runner. More well adjusted individuals, I am reliably informed by my wife (the normal one referred to on our doormat that says, “A pilot and a normal person live here”), do not often discuss the relative merits of castellated versus prevailing torque nuts. At least not out loud or at the table, and certainly not in front of guests.

Information comes from many sources, many of them of questionable veracity. Shop manuals, parts guides, service bulletins, and other technical literature published by the part’s manufacturer are far more authoritative than the local airport bums.

So when it happens, a Regular Joe comes up against a non-fluxing periodic encambulator on his RV, he may honestly not know what to do. But endowed with an admirable inquisitiveness and empowered by the FAA to freely educate and recreate himself, he might ask a fellow aviator about periodic encambulators that mysteriously stop fluxing.

Of course the other guy doesn’t know any more about encambulators than the first guy, other than he saw an A&P change one once, and that guy said those things were all junk nowadays and wished we’d go back to oil-lubricated encambulators. They made a sticky mess under the cowling but at least they never failed. The guy in the hangar across the taxiway says he’s never seen an encambulator—dry or oil-lubed—go bad unless you were doing hard acro, and the guy next to him insists it’s just the drive section of the encambulator that gets sloppy. Change it and it will start fluxing again. “They’re just ripping you off by changing the whole thing,” is his bottom line.

Thinking maybe a pro would know more, Regular Joe asks his A&P what he knows about periodic encambulators. “Oh, it’s the same price to change the whole thing as to just replace the drive unit, so we just change ’em out. We used to rebuild them, but I had a few quit early, so I just install factory rebuilds now. They’re $700 installed; the Chinese ones are about $375 from Spruce, or a new one from Acme is about two grand.”

After all that, Regular Joe still doesn’t know anything fundamental about his periodic encambulator or what he should do about it. It was the same for me when my 540’s oil pressure and temperature migrations toward the red arcs became more than I could wish away. The temperature would head for the red in a hurry; a few minutes of cruising and it was at least 220 F and rising. But it was the oil pressure that really got my attention. It was just in the high 50-psi range, and as the oil temp got over 200 F, the pressure gauge needle would quiver rapidly in a 5-psi swing. Weirdly not reassuring.

Now, after researching and writing about car engines for 30 years, I probably understand more about infernal combustion engines than the next Regular Joe, but for very human reasons exactly what was “wrong with the oil” eluded me for too long. Of course I chatted up the issue with everyone within earshot and everybody had a different answer. I was told to shim up the oil pressure relief valve as sometimes the springs get weak (and a guy gave me a new spring, and I put it in); that the engine was tired but to just top the engine as “the bottom end never wears out”; to fit a larger oil cooler; to use a different oil cooler location; to louver the lower cowling; to detail my cooling baffles; or to change just the oil pump.

All the while, the obvious explanation of what was wrong simply would not land between my headset earcups—the engine was worn out and needed a major overhaul. But that’s a $30,000 bill, and I didn’t have $30,000, so that could not be the problem. It had to be something simpler and less expensive.

Shrinks call this observational bias. We want to go flying, the weather is marginal, but we tend to pick out the promising bit in the forecast and tell ourselves we can make it. Or that a clearly ailing 540 just needs its oil pressure relief valve spring changed.

My epiphany came about 15 minutes into a four-hour cross-country. The oil temp was already 235 F, the pressure needle a buzzing blur, and I had hours to go in the summer heat over the 8000-foot mountains. Like a switch flipping, the little voice said, “Tom, what does this engine have to do before you’ll start listening to it? Do you really need to stare at a stationary prop blade?” And just like that, I rolled left 70 degrees and pulled three G’s into a 180-degree heading for home. I couldn’t get on the ground fast enough.

With the Starduster heating the hangar, I asked myself, “What if you were an A&P and this thing taxied up in front of your shop? How would you evaluate this problem?” That got me thinking Lycoming must have some literature on evaluating engines. So I walked down to my A&P’s hangar and asked him if there was something by Lycoming like that. I was instantly handed a Lycoming overhaul book. And in the front were a few paragraphs about evaluating these engines, and part of that was a list of specific circumstances—something along the line of, “TBO is what it is, but if any of the following have occurred, TBO is reduced.” The list had things such as aerobatics, banner towing, periods of inactivity, and so on. Of the 20-odd conditions listed, my engine had seen something like 13 of them.

It took six and a half years to get the engine overhauled and flying again. I learned a lot about Lycomings along the way and just how comprehensively worn-out mine had been. But more importantly, I learned something about myself and where I get information from.

Perhaps the strongest lesson was to be truthful with myself. So often we know the right thing to do but justify a less painful solution to ourselves.

Another lesson is to forget your friends. Your buddies are no doubt fine airline pilots or neurosurgeons, but they have no background in oiling systems or inner tubes, for that matter, and their opinions on those subjects may be strongly stated but are not developed with a complete understanding of the subject. But the people who make inner tubes know a heck of a lot more about them than just round and black, and that’s where you should be directing your questions. Look for published advice, the sort someone thought important enough to print on paper and distribute to the working pros out in the field. And yes, much of this is on the internet, but the signal-to-noise ratio on the net is incredibly poor, so be very careful in the electronic jungle.

Beware of simple solutions and terse, one size fits all responses. The world is a complex place, and even the simplest airplane question involves plenty of variables. It often takes time and mental effort to sort them out.

Pay attention to who’s talking and what their experience is. Your airport buddies may have flown a cumulative 100,000 hours behind piston engines; one or two may even have “overhauled” one once. But what they did was assemble parts made or rejuvenated by others while the better engine shops may machine and assemble 300 engines a year. The guys at the engine shop may look like a bunch of farmers, but you can set your engine compass to the heading they give you.

Beats staring at a stationary prop blade.engine

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Tom Wilson
Pumping avgas and waxing flight school airplanes got Tom into general aviation in 1973, but the lure of racing cars and motorcycles sent him down a motor journalism career heavy on engines and racing. Today he still writes for peanuts and flies for fun.


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