>>Sounds to me like maybe one of your valves has bit the dust.  Probably number
>>3 exhaust valve.  Let us know what you find when you pull the head off (it is
>>probably not going to be pretty).  If it is #3 exhaust valve then this is
>>usually due to overheating.
>>Ken Wilford
>
>Vanagons don't show a preference for munching any particular exhaust valve,
>unlike the type I aircooleds. In fact, with a water cooled engine, you have
>a lower possibility of having exhaust valve problems, and thus more intake
>valve failures per exhaust valve failure.
>
>To me it sounded like a seat might have fallen out.

My 85 Vanagon just had this valve seat problem. It came unseated and made a
noise quite like a valve lifter. At first I didn't hear anything, just felt
a dramatic loss of power (mechanic says I would have lost all power from
both cylinders in the head) then power returned to normal maybe 30-60
seconds later.  It was a half hour later that I stopped at a toll booth and
heard the noise when I rolled down the window. It kept driving like that
for 7 hours (Pennsylavania to Ottawa Ontario) and for another couple of
days.  While being diagnosed it unseated another time, and the noise went
silent then reseated and the noise returned. When the head was removed the
seat was found to be loose and the piston was burnt, I guess from the 7
hours not properly scavenging heat?
>