Ken and fellow listers,

I have seen this exact same thing happen to two different aircooled
engines; once in my 912 as 201K miles and once in a 40hp VW type1 engine
we had in our shop many years ago.  Harry Pellow (the Porsche 356 guru)
talks a lot about this in his technical books.  It was a very common mode
of engine failure seen in four-cylinder Porsche engines during a period of
the early 1980's when the quality of gas was really bad.  The probable
cause is predetonation.  You should expect that the other pistons are
damaged also; your customer should be warned that a whole new set of
pistons and cylinders may be required.   Pull the other pistons; inspect
the rings and measure all dimensions carefully.

What happens is that the engine is predetonating (pinging) due to
overheating, load, bad timing, bad gas or some combination of the group.
The piston gets so hot that it loses structural intregity. The the rings
remain intact longer as they are made of a harder metal.  The rings smash
the heat-softened piston ridges between the rings to bits, the bits
eventually perforate the top of the overheated piston and get pummeled
against the head.  These are the pieces that you found in the combustion
chamber.  In my 912, several pieces were embedded in the head and required
considerable effort to dislodge them.

As to whether or not VW will cover any of the cost is anybody's guess.  I
think that it would be worth the try for your customer, but keep
expectations low.  40K miles is not acceptable wear, but it is well
outside of the warranty period.

Regards to all,
Jon Kanas
Longmont, Colorado
Cultural Center of the Universe
303-678-0658
kanas@qadas.com