RJohn15183@aol.com wrote:
In a message dated 2/27/99 3:52:21 PM Central Standard Time,
rotaryeng@earthlink.net writes:
One of my customers has an O-200
built in my shop that has no appreciable oil consumption in 173hrs.
I'm probably getting in over my head but reading Archie's e-mail reminded me
of an article I read a few month's back, so I went and dug it up
The following is a snip from an article called "The Ten Biggest Lies
About Piston Aircraft Engines"
begin snip
Lie #5:
The less oil an engine burns, the better.
Get a few aircraft owners get together over a few beers, and inevitably the
conversation turns to oil consumption. "I'm only using a quart in 30 hours,"
one will say. "That's nothing," brags another owner, "I don't have to add any
make-up oil between 50-hour oil changes!" The owners 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.
For a cylinder to make it to TBO, it must be protected from metal-to-metal
scuffing by the piston rings. This protection comes from a film of oil that
coats the cylinder barrel and causes the rings to "hydroplane" instead of
scuffing the barrel.
Now, if the cylinder barrel is properly coated with oil, it's inevitable that
some of this oil will be burned up in the combustion process. That's why a
certain amount of oil consumption is perfectly normal.
Ultra-low oil consumption indicates one of two things: either the oil film is
too thin, or the oil is not reaching the critical upper portions of the
cylinder walls where the compression rings reverse direction at top-dead-
center (the so-called "ring-step area"). Without adequate lubrication, there's
a high risk of metal-to-metal contact between the compression rings and the
cylinder wall.
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.
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 hours
may well be too much of a good thing.
end snip
The full text can be found at:
http://www.avweb.com/articles/englies.html
Rob
OK guys hold this subject down. We don't really give a hoot about
piston engine oil consumption on here :-)
PL
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