Subject: DML: Heres the final blown 318 pics for a while... got the head
off...
Tim,
I'm in agreement with Tom Slick. The absence of a head on the end of the
exhaust valve stem points to valve stem failure. The large, uncompressible
chunk of metal dropping into the chamber would definitely frag the piston on
the next up stroke. If the piston disintegrated first, the pieces would have
hammered the valve face but probably not broken the stem that far up.
The engine on my first car, 34 years ago, blew up in pretty much the same
way. In my case, it was a '65 VW that I bought from the original owner. I
ran it for a year and a half on Amocco premium, for the "extra power". At
that time it was the only unleaded gas available. Lots of WOT Thruway
driving without any lead additive on the valve stems eventually led to stem
failure. #3 cylinder ran hotter the other three because the oil cooler tower
inside the fan housing blocked a lot of the airflow to that cylinder head.
VW's that were abused were notorious for swallowing #3 exhaust valve. While
on my way back to Sub School at Groton after a weekend at home, doing about
70 mph on I-95 in Connecticut, the engine went "bang". It left the
connecting rod and wrist pin intact and the biggest chunk of piston was less
than an inch in diameter. The end of the spark plug was peened over, the
cylinder head was trashed, the skirt on the cylinder jug where it inserted
into the engine case was broken, and pieces of piston that hit the crank
counterweights were blown through the top of the engine case behind the
generator. Not pretty and not rebuildable!
The broken end of your exhaust valve stem may "yield" some clues.
Neil
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