Consommation d’huile élevée!
Posted: Thu 14 Dec, 2006 15:11
Tien tien un sujet dont j’entend très souvent parler me semble. J’ai toujours dit que je trustais plus un moulin qui prend 1 litres aux 5 heures que un qui en prend pas pour 50heures. :shock: :shock: :idea: :arrow: Ben voila lisez ceci c’est en anglais je sais mais j’ai pas le temps de le traduire ça prend toute pour prendre le temps de lire!!! :roll: :roll: :wink:
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.
voici le lien sur larticle complet.
http://www.avweb.com/news/maint/182902-1.html
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.
voici le lien sur larticle complet.
http://www.avweb.com/news/maint/182902-1.html
