Rapping Noise Upper End 1986 Graduate

[Petown@xxxxxxx]

I've got an intermittent tapping or rapping noise coming from, I think, the 
#1 cylinder area of the engine.  It comes and goes at idle and can be heard 
clearly from the driver's seat with the hood down.  Trying to "force" the noise 
by blipping the throttle doesn't seem to have any effect.  I tried switching 
the a/c on, though, and got an immediate and sustained noise as long as the 
compressor was on (the a/c is never used).  I then turned the a/c off and the 
noise was again intermittent, rapping for a while then quiet.  I set the parking 
brake and fed a little clutch starting to drag the engine against the brake and 
got the noise again.
I've checked the valve clearances and retensioned the timing chain.  When I 
changed the head gasket last year (car was supposedly low mileage but had sat 
for years), I found scoring on the #1 cylinder; the others were unmarked.  The 
spark plug on #1 is always dirtier but not noticeably oil fouled.  I tried the 
screwdriver-to-the-ear technique and listened at several areas at the head 
but, frankly, don't know what I'm doing.  I thought I could pick up a similar 
noise, though, when listening at the #1 exhaust header.  Any ideas?  Thanks in 
advance.

Ed  
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