Sticky valve_Lycoming IO-360-A3B6D

[wishboneash]

 

Ash, can you specify a first-run rebuilt cylinder next time around?   The R&R labor will more than cancel out the 1100$ in savings on a rebuilt unit if it goes bad again.  And its gone bad twice already in 250 hours.

 

Air West confirmed the borescope result. Intake valve seat lifted out. Very rare event to say the least. They think the wrong sized seat was installed on last overhaul. I am done with this cylinder.

[TWinter]

Mine is in for annual. Got "the call" this morning..Compressions are 2,3,4 in the 70s, but cylinder #1 is 30 .

Cylinder hopefully off by this afternoon and sent out to be checked out, looks to possibly be exhaust valve. Not sure yet.

Plane was flying great, no issues. Still learning the JPI as far as engine reports. No "Morning Sickness" as we have been calling it here.

Not sure why there was no indication. Engine EGTs where always very good. I have not stopped by the shop yet.

[fantom]

Not sure why there was no indication. Engine EGTs where always very good. I have not stopped by the shop yet.

 

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).

[TWinter]

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).

 

Great info..I must admit I fall into at least one of the "Don't do items",

 

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.

 

I'm usually at full rich well in advance of this point, but something that I will make mental note of. I'm sure I've cut it closer than what I should have a few times.

[wishboneash]

Mine is in for annual. Got "the call" this morning..Compressions are 2,3,4 in the 70s, but cylinder #1 is 30 .

Cylinder hopefully off by this afternoon and sent out to be checked out, looks to possibly be exhaust valve. Not sure yet.

Plane was flying great, no issues. Still learning the JPI as far as engine reports. No "Morning Sickness" as we have been calling it here.

Not sure why there was no indication. Engine EGTs where always very good. I have not stopped by the shop yet.

 

What is your EGT reading on cylinder 1 at low RPMs? Last year, when I first had problems with this cylinder, I was seeing a big difference in EGT between cyl 1 and others. The plane ran fine when the power settings were 60% or higher. This is an early warning sign of impending failure or full loss of compression. In my case I had zero compression and the plane still ran fine. Idle was a bit rough, that's about it.

[aaronk25]

Well if its any consolation I just had my #2 jug pulled because I went from burning a quart of oil in 10 hours to a quart in 3 hours and a worn intake valve guide appears to be the trouble.

We thought we were going to find a broken oil control ring but ended worn valve. Curious though another symptom was oil dirtying quicker than normal and I don't know how a worn valve intake valve guide could cause that? LOP and camguard, but I guess sometimes things still go wrong.

Aaron

[KSMooniac]

LOP and Camguard can't fix bad installation/assembly geometry.  

 

I never go full rich except for takeoff from lower elevations and on go-around at lower elevations.  Teaching full rich on final is bad bad bad but everyone was taught that way...

[aaronk25]

Ya not sure what did it in as the heads have never been over 400, rarely 380 almost always 350-360, but there is one exception. When the Willmar ferry pilot returned my plane to me (they don't believe in lean of peak operation) he got the #2 up to 430 degrees. Not sure how he did this but when I told them I run lean of peak and it helps keep head temps down I was told running LOP will wreck my cylinders in 100 hours.....lol 300 hours of peak egt at 4k,6k 8k and compressions are 76 but I feel these guides were junk to start with or got put in wrong.

Maybe that one hot flight set up a scenario for premature failure.....

[KSMooniac]

and that is a good reason to not let just anyone fly a plane you own!  I would be livid if he let a cylinder get that hot.

[aaronk25]

Its amazing what a tattle tale a JPI 830 can be.....

[bnicolette]

About 5 hours of flight time after getting my #1 valve guide reamed out I started noticing my #2 EGT starting ever so slightly to consistently dip about 1 min after the first start of the day.  It did this for the last 5 flights I have done and never did it after the first start of the day.  So, I flew it down to Tom at Aero Engines of Winchester this morning for a reaming.  I landed at 7:40am and was back in the air at 9:40am.  Those guys there at that shop are first class all the way!  Anyhow, we did find that the #2 valve guide was tight so he reamed it out.  He suggested that I start running TCP and that should keep the carbon away from building up in the guides.

 

#1 has been flawless since we reamed it out.

 

 

[mcpilot]

Ream early and ream often

[Marauder]

About 5 hours of flight time after getting my #1 valve guide reamed out I started noticing my #2 EGT starting ever so slightly to consistently dip about 1 min after the first start of the day. It did this for the last 5 flights I have done and never did it after the first start of the day. So, I flew it down to Tom at Aero Engines of Winchester this morning for a reaming. I landed at 7:40am and was back in the air at 9:40am. Those guys there at that shop are first class all the way! Anyhow, we did find that the #2 valve guide was tight so he reamed it out. He suggested that I start running TCP and that should keep the carbon away from building up in the guides. #1 has been flawless since we reamed it out.

Hey Brett. Stick this one on the troubleshooting thread. Different look than your last valve issue.

[bnicolette]

Hey Brett. Stick this one on the troubleshooting thread. Different look than your last valve issue.

 

Oh yeah.  I forgot all about that thread.  Thanks Chris. 

[tony]

About 5 hours of flight time after getting my #1 valve guide reamed out I started noticing my #2 EGT starting ever so slightly to consistently dip about 1 min after the first start of the day.  It did this for the last 5 flights I have done and never did it after the first start of the day.  So, I flew it down to Tom at Aero Engines of Winchester this morning for a reaming.  I landed at 7:40am and was back in the air at 9:40am.  Those guys there at that shop are first class all the way!  Anyhow, we did find that the #2 valve guide was tight so he reamed it out.  He suggested that I start running TCP and that should keep the carbon away from building up in the guides.

 

#1 has been flawless since we reamed it out.

what's TCP?

[bnicolette]

Expensive marvel mystery oil. :-)

No, here it is: http://www.alcorinc.com/index.php/products/tcp-fuel-additive-qt/

Sent from my iPad using Tapatalk HD

[tony]

I hope it has the same minty fresh smell.....

[Jsavage3]

I started noticing my #2 EGT starting ever so slightly to consistently dip about 1 min after the first start of the day. 

 

This is good to know.  I had gone with "it's running rough" but this helps clear up in my mind what to look for on the engine monitor when a valve is starting to stick...and you know which cylinder is acting up too!

[mcpilot]

what's TCP?

TCP is a catalyst to help burn off the lead... It "softens"  it.   Actually it changes the physical properties so it can be removed during combustion.  I have been using it for quite awhile with really great results.  That coupled with an inexpensive ($99.00 )  intraoral camera will go a long way to helping to deal with the sticky valve problems that seem to be more the rule than the exceptions with our planes.  TCP is very different from MMO....

[Jsavage3]

Aircraft Spruce is selling TCP for $38 a quart.  How much TCP gets added to the fuel...i.e. how quickly will one burn thru a quart of TCP?  With a top-off, I have 64-gal useable...  Also, can you expound on the differences between TCP and MMO?

[mcpilot]

1 oz of TCP per 10 gal  100LL

 

MMO is a solvent as far as I have heard.  It has been added to fuel and oil with many anectdotal reports of good results.  It is not FAA approved as a fuel or oil additive.  The oil manufacturers go to great lengths to get the formula for their products just right. I am not a believer in messing around with their good science....

[DaV8or]

TCP is a catalyst to help burn off the lead... It "softens"  it.   Actually it changes the physical properties so it can be removed during combustion.  I have been using it for quite awhile with really great results.  That coupled with an inexpensive ($99.00 )  intraoral camera will go a long way to helping to deal with the sticky valve problems that seem to be more the rule than the exceptions with our planes.  TCP is very different from MMO....

 

Any evidence yet with your camera that the TCP removes existing lead deposits? My guess is, it only helps burn off the lead that is in the gasoline and little, to nothing for lead deposits already in the cylinder. Love to be wrong though.

[mcpilot]

Any evidence yet with your camera that the TCP removes existing lead deposits? My guess is, it only helps burn off the lead that is in the gasoline and little, to nothing for lead deposits already in the cylinder. Love to be wrong though.

 

That's what I'm in the process of looking at now.  My plane is out of service while the new JPI EDM830 is getting installed... I would be happy to offer my scope to anyone willing  to stop by KFWQ who would like to do a before and after of their cylinders...

 

Brett?

[N9201A]

9201A,

Are you associating the aggressive leaning to the stuck valve?

LOP ops are known? for cleaner burning engines.

I was expecting fewer stuck exhaust valves if LOP were to be increased accross the Mooney family.

Then again, what is the the actual cause of the stuck valve? What does the rope trick clean out of the guides?

Carbon from oil cooked after shut down?

LOP would generate lower CHTs during flight, lesser opportunity for cooking the oil.

Honest questions, thinking out loud...

My C's stuck valve occurred after sitting for years, combination of carbon and rust???

Best regards,

-a-

 

No the leaning I am talking about is ground-leaning.  My experimentation has not yielded smooth running LOP on my IO360, but I understand that others have had success.  My CHTs rarely get to 370 and I NEVER permit them to exceed 380.   

 

My IA reamed one cylinder's valve guides but only after replacing the jug, a completely unnecessary expense.

 

My hangar is quite a taxi from the landing zone, so I suppose oil could cook but I don't know what else I could do than the ten-minute idle taxi to hangar that I have now.  

 

Thanks for your thoughts.  

[Jsavage3]

Sticky valve update...  

 

I now have put 13 hours on the engine and 7 engine starts (4 of them a first-start-of-the-day) and I am happy to report zero issues regarding the original sticky valve situation that I first described.

 

Flew the family from Ohio-Iowa-Oklahoma-Ohio in 12.2 hours on the tach and 120 gallons of av-gas!  For a family of 4, I cannot think of a more efficient & economical mode of transportation!

 

Happy (and relieved) Mooney driver here!