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Interesting data from AvWeb: How Cylinders Wear Out When a cylinder needs to be replaced, it is almost always for one of three reasons: metal fatigue, barrel wear, or valve problems. Metal fatigue failures are the culmination of repeated mechanical and thermal stresses. They are increasingly likely in high-time cylinders, particularly reworked cylinders that have been weld-repaired and kept in service for two or three TBOs. The aluminum head casting gradually becomes embrittled and more vulnerable to cracking. Head cracks are the most common sort of fatigue failures. They usually emanate from a spark plug or injector hole. Fatigue can also cause catastrophic failure of the head-to-barrel joint. Fatigue failures are more common in turbocharged and other hot-running engines, particularly if pilots are not meticulous about avoiding rapid throttle and mixture changes. For example, RAM Aircraft Corp. in Waco, Texas, is a premier overhaul facility that specializes in high-horsepower turbocharged Continental TSIO-520 engines. They were plagued by warranty claims due to head cracks. Finally, in 1988, RAM decided to start using only factory-new cylinders on their engines. Head crack problems dropped precipitously after that. Barrel Blues Barrel wear usually manifests itself by increased oil consumption and deteriorating compression test scores. It doesn't take much wear to do a cylinder in—most cylinders become unairworthy (beyond service limits) if any portion of the bore measures more than .005" above new dimensions. Fortunately, cylinder barrels incur zero wear during normal climb-cruise-descent operation. This is because there is normally no metal-to-metal contact between the cylinder wall and the piston rings. The cylinder wall is coated by a thin oil film, and the rings hydroplane on this film. For this reason, it's quite common to tear down a high-utilization Part 135 engine at TBO and see the original hone microfinish along the full stroke. So why do some cylinders suffer significant barrel wear? Hot-running high-horsepower engines (particularly turbocharged ones) tend to suffer barrel wear because the high combustion pressures and temperatures can breach the oil film under extreme conditions. Low utilization is another major culprit. During periods of disuse, the oil film that normally adheres to the cylinder barrel has an opportunity to strip off—particularly if multigrade oil such as Aeroshell 15W-50 or Phillips 20W-50 is used. This has two adverse consequences: corrosion and dry starts. If the cylinder walls are steel, the loss of protective oil film leaves the barrel vulnerable to corrosion. Rust pitting will eventually destroy the cylinder's ability to hold compression. Chrome-plated barrels are relatively immune from such corrosion, which is why they are particularly popular in highly corrosive environments (e.g., near the ocean or in humid climates). Even where corrosion is not a problem, the loss of oil film during periods of disuse results in a dry start—a brief period of metal-to-metal contact between the rings and the cylinder wall until sufficient oil splash has occurred to replenish the oil film on the cylinder walls. Corrosion and dry starts explain why low-utilization owner-flown airplanes often fail to make TBO or require a mid-time top overhaul. On the other hand, freighters and flight-school ships that fly every day often go well past TBO without needing top- end work. Cold Starts Cold starts spell disaster for cylinders. A single unpreheated cold start (particularly at temperatures below 20 F) can inflict more cylinder damage than a thousand hours of cruise flight! Contrary to popular belief, cold start damage isn't caused by lack of lubrication, but rather by loss of piston-to-cylinder clearance. This requires some explanation. When an engine is cold, there is quite a lot of clearance between the piston and the cylinder walls—usually more than .010" of clearance. This is necessary because as the engine heats up to operating temperature, the aluminum piston will expand about twice as fast as the steel cylinder barrel will, and the piston-to-cylinder clearance will get a good deal tighter. And that's okay. But it's crucial that there always be at least a few thousandths clearance between the piston and the cylinder wall, so that the the oil film is not breached and metal-to-metal contact is avoided. During a cold start, the piston heats quite quickly, but the cylinder warms up much more slowly because it has vastly greater thermal mass and is covered with cooling fins and bathed in frigid air. Consequently, there is often a period of time—where the piston is up to temperature but the cylinder hasn't caught up yet—when the piston-to-cylinder clearance can actually go to zero and result in metal-to-metal scuffing of the piston and cylinder walls. That's why cold starts can be so devastating to cylinders. Ultra-Low Oil Consumption Every time a group of aircraft owners get together, it is inevitable to hear at least one or two bragging about ultra-low oil consumption. "I'm using a quart in 40 hours!" These super-low oil consumption figures are often associated with Cermicrome cylinders, and/or with Continental engines equipped with the late-style center-vented oil control ring. The owners who are doing this bragging probably don't realize that they probably won't make it to TBO without a costly mid- term top overhaul! It turns out that ultra-low oil consumption is often a bad omen when it comes to cylinder longevity. Here's why. The maintenance of the critical oil film on the cylinder walls is acomplished by the oil control ring, a fancy spring-loaded perforated double-ridge ring that receives a supply of oil through small holes drilled through the piston wall and spreads it into a thin film as it moves up and down over the cylinder walls. The oil control ring is installed in the third piston groove, below the two compression rings that are resonsible for maintaining the dynamic seal of the combustion chamber. Consequently, the oil control ring lubricates most of the cylinder wall, but it never reaches the topmost inch or so where the compression rings reverse direction at top-dead-center—the so-called ring-step area. Lubrication of this critical region can only take place if sufficient oil is allowed to flow past the oil control ring. A certain amount of this oil is inevitably burned up in the combustion process. If oil consumption is reduced to an ultra-low level by means of a tight-fitting oil control ring (like the new-style center-vented Continental ring) or a super-smooth cylinder wall finish (like Cermicrome), it's very likely that the ring-step area won't receive adequate lubrication, and there's a high risk of metal-to-metal contact between the compression rings and the cylinder wall. A "blued" ring-step area is a sure sign of such lubrication failure. Experience seems to indicate that oil consumption lower than about a quart in 20 hours may not bode well for long cylinder life. Barrel wear in the ring-step area becomes likely, leading to rapidly deteriorating compression and accelerating oil consumption at 500-1000 hours. Once again, this tends to occur most often in hot-running high-horsepower turbocharged engines. While low oil consumption has always been acknowledged as a sign of a tight, well-broken-in engine, there is strong evidence that a quart in 30 or 40 may well be too much of a good thing. Cermicrome cylinders are particularly vulnerable to such ring-step wear. This is because the ceramic-impregnated layer of a Cermicrome barrel is extremely thin—a thousandth of an inch (.001") at best. Once this very thin ceramic-impregnated layer has been worn through, what's left is mirror-shiny chrome which is not oil wettable. Once this happens, there's no oil film in the ring-step area, so there's nothing to prevent metal-to-metal contact between the compression rings and the cylinder wall. Naturally, things go to hell rather quickly after that. Stuck Rings Bad things also happen if too much oil is allowed to reach the compression rings due to a loose oil control ring or an excessively rough cylinder barrel. The compression ring grooves may fill up with oil, the oil may be cooked into varnish by the heat of combustion, and ultimately the compression rings may become stuck and unable to flex or rotate. Stuck rings are usually revealed as a sharp and sudden increase in oil consumption, and often accompanied by oily top spark plugs. If caught early, rings can sometimes be unstuck without cylinder removal by means of a penetrant soak. Sometimes pulling the cylinder is unavoidable. Exhaust Valve Leakage If you are fortunate enough to avoid metal fatigue and barrel wear problems, your cylinders will ultimately be done in by exhaust valve leakage. This is unavoidable. Exhaust valves are the most thermally stressed components of the engine. They operate at rediculously high temperatures, so they have to be manufactured from the most exotic and expensive high-temperature alloys (such as Inconel and Nimonic-80). What's worse, exhaust valve stems must slide back and forth in their guides with extremely close tolerances and virtually no lubrication. Any oil introduced into the guide would quickly be fried into varnish by the extreme heat. Lubricant would also interfere with the critical stem-to-guide heat path through which the exhaust valve sheds its heat. Consequently, metal-on-metal contact between the valve stem and guide can't be avoided, and guide wear is simply a fact of life. As the guide wears, it can no longer hold the valve in perfect alignment with the seat. The valve starts to wobble and no longer seals perfectly against the seat every time it closes. Hot exhaust gas leaks between the valve and the seat, causing both to overheat and warp. The warpage allows even more exhaust to leak, which results in even more overheating and warpage. This condition is commonly referred to as a burned valve. Once leakage starts, compression deteriorates rapidly. If not detected in time, the valve may fracture and a catastrophic engine failure may result. Continental and Lycoming have made numerous changes to exhaust valve and guides in order to increase TBOs. In the 1960s, valve guildes were usually made of bronze which was relatively soft and didn't wear well. Both manufacturers have switched to harder aluminum-bronze alloy and cast iron "ni-resist" guides, and Continental even tried super-hard nitrided steel "nitralloy" guides for awhile. Harder valve guides demanded harder valve stems, so exhaust valve stems are now often chrome plated. These valves and guides are capable of making it to TBO and beyond if everything goes just right. But if it doesn't, they won't. A common cause of premature valve problems is failure to lean sufficiently, particularly during ground operations. Rich mixtures and low combustion temperatures will cause a build-up of lead salts and other combustion byproducts on the valve stem. This buildup tends to be crusty and abrasive, and it can quicly abrade the lower portion of the valve guide into a bell-bottom shape, allowing valve wobble, leakage, and burning. If an overhaul or cylinder shop isn't meticulous about guide-to-seat concentricity or rocker arm geometry, the valve is sure not to make TBO. This seems to be a disturbingly common problem. We've even seen quite a few reports of Continental factory-new power assemblieswith serious valve misalignment problems right out of the box. We've talked to several top-rated overhaul shops who tell us that they don't dare install a factory-new cylinder without first checking valve alignment. (Really makes you wonder about TCM factory remans, doesn't it?) Cylinder Longevity Tips Here's our advice about how to increase your odds of nursing those jugs to TBO without intermediate top-end work. Be careful about what cylinders you have installed on your engine. Don't try to recondition a cylinder too many times. The likelihood of head cracks and separations increases after about two TBOs time in service. Avoid exchange cylinders like the plague—you have no way of knowing where those heads have been. Be sure your overhaul or cylinder shop reams the valve guides to be precisely concentric with the seats. Concentricity needs to be checked even with factory new cylinders. When you fly, become obsessive-compulsive about thermal cycles. Avoid rapid throttle and mixture changes. Throttle-up slowly and smoothly during takeoffs and go-arounds. Avoid high-speed low-power descents. Avoid going full-rich on final approach if your engine is fuel injected. Fly often. Avoid extended periods of disuse. If you can't, hangar your airplane and consider using single-weight oil such as Aeroshell W100 for corrosion protection. There's nothing wrong with using multi-grade oil during the coldest months and switching to single-weight oil for the rest of the year. In fact, that's an excellent procedure. Never cold-start without a preheat. Don't even consider it. An unpreheated start below 32 F is harmful. Below 20 F it's a capital offense. A night in a heated hangar is the best preheat. Sleeping late in the morning is also a useful technique. If you need to reposition your airplane on the tarmac, don't taxi it if you can have it towed. Remember that most barrel wear occurs at engine start. So try not to start your engine unless you're going flying. Lean aggressively. Particularly avoid full-rich mixture during ground operations. Rich mixtures and low combustion temperatures often result in accelerated exhaust valve guide wear. Beware of ultra-low oil consumption. An engine needs to burn some oil in order to achieve needed lubrication of the critical ring-step area. 10 to 15 hours per quart is great. It's perfectly normal for oil consumption to increase toward the end of the oil change interval. Shun new cylinder coatings, rings, valves, guides, rockers, and other wonderful-sounding innovations until you're sure that they've been in the field long enough to prove their ability to make TBO in your type of operation. When to Replace a Jug Sometimes it's necessary to pull a cylinder and rework or replace it. But such top-end work is often done unnecessarily. Top overhauls (replacing some or all cylinders at mid-TBO) is one of the most over-sold maintenance procedures in general aviation. It is common practice at many shops to pull any cylinder that measures less than 60/80 on a differential compression check, and to recommend replacement of all cylinders if two or more cylinders measure that low. Some IAs simply refuse to sign off an annual if any compression reading is less than 60/80. Such procedures are simply unfounded and erroneous. Never allow a cylinder to be pulled on the basis of a single compression test. For one thing, the standard differential compression test is notorious for giving non-repeatable results. A cylinder that tests 55/80 today might easily test 68/80 after two more hours in service. Mechanics should treat compression readings the way doctors treat blood pressure readings: no conclusions should be drawn until at least three successive measurements have been taken to establish a baseline. In the case of aircraft engines, the measurements should be separated by at least a few hours of operation. Furthermore, there's nothing magic about 60/80. It's quite common for some engines to operate quite happily with compression readings in the 50s. Anytime a questionable compression reading is observed, it's important to determine where the compression is being lost. If air can be heard escaping from the exhaust pipe, then the exhaust valve is leaking...a potentially serious problem, and one likely to deteriorate fairly quickly. On the other hand, if air is heard coming from the breather line or oil filler cap, the leakage is coming past the rings...a much less worrisome situation. In fact, low compression readings due to leakage past the rings can probably be disregarded unless it is accompanied by an alarming increase in oil consumption. If a cylinder exhibits a deteriorating compression trend over several readings, or if low compression is confirmed by at least one additional symptom (elevated oil consumption, rough running, anomalous EGT readings, metal in the filter, etc.), go ahead and pull it. But don't let the mechanic talk you into "topping" all the cylinders just because one has gone soft. A complete top overhaul is seldom justified (unless part of a carefully planned TBO-extension program).

My C had the smell when I bought and I knew what it was. I ordered two rubber gaskets for the fuel senders from Lasar,I think something like $8. The gaskets have holes that match the screws that hold the fuel sender to the wing root. I did it myself (with A&P supervision of course) and saved lots of labor because a lot of things have to come out in order to access the senders, nothing from the floor though. Also I used as much fuel as I dared in flight and removed whatever was leftover. After I removed the side panels I could observe the stains surrounding the sender where fuel had been leaking for a while. It should have been caught during an annual, but the airplane had been sitting in between annuals because the owner had died after a long illness. It was an issue, among others, for price negotiation.

I have the same invitation as Bob. So... If someone would like to attend the event, let me know. I will arm with you pictures just in case they don't believe you are an Aspen customer.

It wasn't so bad - actually sort of fun - as a one time thing....as I said I would not want to test engineer a whole plane, but one instrument was fun. I did it with Hobie from BTV who is a 35,000hr CFI/DPE pilot with all sorts of airline, military and aerobatic experience. I felt quite comfortable with him. I now know exactly where my clean, and each of the degrees of flaps stall speed is. I am pretty sure my stall is a bit slowed by my VGs by the way. I am stalling at 52IAS dirty which is slower than most rockets I think. With Hobie, and for repeatability, we were holding it right before the very beginning of stall for 30 seconds at a time. This alone was well worth the trouble to refamiliarize myself with slow flight in a more substantial way than I ever did during my PPL or any previous BFR.

Fly Tester, thanks for taking time for providing interesting and useful comments. In my previous life as gainfully employed I had many working trips to India and one of them included a few days in Calcutta. I remember that it was hot but not as hot as this past week in the Washington DC area. Of all the countries I visited, to this day India remains as the most incredible and fascinating place on earth and I don't think they had reached the billion people (now 1.2) when I was there!!!

i/m thinking a hulagirl/ mag compass setup.

But don't underestimate what a**holes 'potential' buyers can be, especially when they perceive a buyer's market is a license to steal.....thus wasting the seller's time. It works both ways.

thoughts from a machine sales guy... When it comes to buying and selling expensive items... (1) what is expensive? Expensive to one person is pocket change to another... Life is unfair. (2) On experience, the more experience you have in buying or selling similar machinery at a similar price, the better off you will be... (3) On markets... Markets are a function of time and location. Planes for sale, don't change location much. The buyers ussually have to travel to see the plane. Some sellers have plenty of time to sell their planes. Often, the rest of their natural lives. (4) On emotions... Decisions can be based at least partially on feelings. When you find the right plane at the right price you will probably still have the feeling that something else is going to bite. This is a good preservation trait, may not save your life, but may save your wallet some day... (5) On competition... There is some competition going on between people looking to buy any item. First, be ready. Then, when you see something that matches what you want. Don't drag your feet too long. (6) There are keys to being emotionally comfortable... (a) Know your mission, the best that you can for the longest time frame that you can foresee. Mission and time frame are personal. ('b) Know what Mooney best fits your mission. ('c) Know your finances, what you can afford comfortably. (d) Know what you will do if a valve sticks or a cam rusts. (e) Know the plane you are buying. There is value in a proper PPI. (f) Know that not all planes are in perfect condition, not all sales people have your best interest in mind. Some are, and some do. (g) know that an individual selling a plane may not have experience in buying or selling anything. He may hold the keys to your next ride. It will take more work from you to achieve what you want. (h) Know that nice planes, sold by ethical people, will feel expensive. If it doesn't, move up to a turbine or a twin... Visit All American's web site for a base line comparison for your research... Thanks, that's my writing exercise for the day. how did I do? Best regards, -a-

G500 arrived today, so plane will be put back together this week. Just my luck that I'd be the last person to buy a product in a series?? We'll see if they are releasing a new product. Not only is the panel taken apart, but the whole interior was removed to run wires I guess? Thanks for the input. Ray

Encounters with weather kill half of the pilots that crash Mooneys. Midairs are a distant thirty-third. For that, I think weather in the cockpit is nearly a requirement, and traffic is a cool novelty. Get the weather gear you like. Worry about traffic later. That said, I'll probably get t-boned next week by a Cirrus pilot who hasnt looked outside since he left Duluth with a new airplane. But the odds are on my side its still a pretty big sky.