On Tue, 25 May 2004 09:50:17 -0500, Barnyard BOb
wrote:

Attempting to improve ones lot by denigrating the established
kid on the block is contemptible and intellectually dishonest.
When no one else cares to answer the cheap shots, here I am.
It's a dirty job, but somebody's got to do it. g

Speaking of denigrating the established kid on the block, did you
catch the information that was presented by a couple of Aussie
aircraft mechanics who took a very scientific look at the Lycoming?
They were mystified as to why the Lycoming, much more so than the
Continental, kept wearing out valve guides way before TBO.

They disected the engine piece by piece and finally noticed that the
hydraulic lifter was virtually identical to the hydraulic lifter that
was used in flathead engines. That turns out to be a problem because
in the flathead engine, the hydraulic lifter does not pass any oil
through it to the valve because the valve itself sits inside the
engine block and is bathed with an oil mist. In other words, the
valve guide is not only lubricated, it's cooled internally by the oil
that gets splashed on it, without any help from the lifter.

Lycoming took this design and turned it horizontal to operate it's
overhead valves. Since the lifter wasn't designed to pass oil through
it, Lycoming modified it by drilling a hole through it. But now there
was a problem: If Lycoming drilled the hole big enough to pump some
oil through the lifter and through the pushrod to the valve stem, it
robbed oil from the lifter itself, which used the oil pressure to
control valve lash. So the oil passage through the lifter was tiny,
allowing very small amounts of oil to the valve stem.

The article showed every attempt Lycoming made to modify the lifter so
that it would pump more oil to the valve stem. Continental does not
have this problem as they are using a different design of lifter,
patterned after the virtual auto industry standard which pumps plenty
of oil to the overhead valves.

Since the valve guides are getting so little oil, they run hot at the
valve stems. This causes excessive valve guide wear. The two
mechanics took great pains to document that no matter where you ran
your engine and what temps you thought you were seeing, the actual
temperatures at the valves stems was much higher than it should be.

Lycoming recognized the problem and probably has recognized it for a
long time, and designed a fix for a particular engine used in the
Mooney. I think it's an O-540. This fix involved routing external
oil lines to the cylinderheads to bathe the valve stems. But they
made the fix for the Mooney only, claiming that the baffling was too
tight and that the Mooney installation promoted a hot engine. The
problem with this is that Mooney consulted with Lycoming on the baffle
design, again, according the the two mechanics.

Back when Lycoming first designed it's engines, flathead engines were
the norm. But things have moved on since then and Lycoming appears to
be in a bind about correcting the situation. It looks like it's a
damned if they do and damned if they don't issue. If they fix the
situation by adopting an entirely new lifter that mimicks the auto
industry, they'll have all kinds of recertification costs, plus
possible law suits from pilot/owners who've paid for the top end
overhauls all these years. But if they don't fix the problem, they
will continue to have premature valve guide wear.

Anyway, that's how I remember the article. Did you read it? Sorry,
don't have the URL anymore.

Corky Scott