I just finished rebuilding the 1.9l engine in a 94 Escort wagon that I bought 'as-is' with a "loud upper engine knock". Sure enough it had swallowed the #4 inlet valve seat. The top of the pistion was peppered with steel chunks, as was the head. Some of the bits got into cylinder #1 too. The car had 92,000 miles, had been driven by a young guy who probably didnt drive consersvatively. The clutch was also worn out.
I got a junkyard engine, replaced its piston rings and main seals, and put that into the car. Its head looked good, and I dont run a car hard - so Im hoping the inlet valve seats stay where they belong.
Now I just have to get the temperature gauge to read properly. The gauge works, the thermistor/sensor checks out -- so I think I have a bad connection on the circuit board of the instrument cluster.

Umm, do some reasearch over on FEOA.net.
Did you replace the intake mainfold with a new one when you put in the engine? If you didn't sometimes stuff in it from the previous damage can get back into the engine. It's a known problem as well.
Using a junkyard head is a really dumb idea, since it will also drop a valve seat. You should have used a new or remanufactured one with the improved valve seats.

I drive like an old lady and my valve seats droped at 72,000 miles.

I re-used the old intake manifold, after cleaning it inside.
I -have- poked around at feoa.net, but I like automotiveforums better.
Like I said, Im hoping the valve seat stays put. I believe they have done so in many thousands of Escorts like mine.