They have chronic oil-starvation problems because the design of hydraulic
lifter they use allows only minimal amounts of oil to reach the
heads.  They've apparently managed to avoid noticing the real problem for
about 25 years, so there's a flock of additional inspection/service
requirements on these engines that don't in fact address the problem.  I
believe your diagnosis is correct....  I came across this data while trying
to understand how hydraulic lifters work a while back, and the paper
describing the Lycoming trouble was a great help to me.

david

At 11:59 AM 1/9/2001, Keith Adams wrote:
>filled valves in Lycoming aircraft engines.  They say the heat
>transferred up the valve causes more valve guide wear and thus problems
>because they heat transferred up the valve stem causes carbonization of
>the oil.  Sounds like they have chronic valve guide problems, and
>someone thought this would be a fix, but it wasn't, so they hate them

David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"