On Wed, 18 May 2005 17:33:58 -0700, "Peter Duniho"
wrote:

What's the cost? Well, I can't speak for the average. But in my own case,
I have had a "mini top overhaul" (replaced one piston, due to leaking rings
on that piston, causing erosion of the piston head), and have had to replace
all of the exhaust valves and guides. I don't even know that this was due
to the turbo-charger, but certainly it seems that the extra heat may have
accelerated the wear, if not caused it entirely.

There was a website devoted to the wear of Lycoming valve guides that
went into design and development of Lycoming engines, and also what
they think is the actual problem causing the premature wear in certain
models of Lycomings.

You probably can find it by Googling "lycoming valve guide wear".

To synopsize, the mechanics who took it upon themselves to research
the problem feel that it is Lycoming's use of a particular type of cam
follower or lifter, that has created the situation (of accelerated
valve guide wear).

Lycoming patterned their original lifter after those used by flathead
engines. Since flathead engines have the valves in the block, not the
head, the lifter design, which was not intended to flow much oil
through it, worked fine.

But when this lifter was used in Lycoming's overhead designs, there
were problems because not much oil was getting to the valve guides and
they suffered premature wear.

Many of the fixes for those engines that suffered the most are fixes
that bring more oil to the valve guide area, according to this well
documented and extensive three or four part article.

But the conclusion of the article is that Lycoming does not have the
in-house engineers to come up with a real fix at this point.

Corky Scott