Lost compression

'02 Focus 2.0 sohc lost compression in #4 cylinder. Well, didn't lose all of it. #4 is at 60 psi, others are 160 or more.
Is this Focus engine prone to any catastrophic failure or do I pursue the usual
suspects like burnt valve, blown head gasket, holed piston, etc?
Somebody *please* tell me this is a chunk of carbon stuck in a valve seat and not something that's going to put me swapping engines for the next week or so.
-- Jack
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On Wed, 30 Aug 2006 I wrote:

Turns out it was a loose valve seat on #4 cylinder. Apparently this is a common failure on some Focus engines. This one had a little over 68,000 miles on it. I found a good used head in a junkyard for $100 and I'm getting it swapped out today. The junkyard guy said they sell a lot of heads to correct this problem.
If this turns out not to be the cause of the dead miss and lost compression, I'll post the results here.
-- Jack
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On Fri, 01 Sep 2006 I wrote:
If anyone cares...

Just came from the mechanic's shop. There is a section of the valve seat missing. Not a big section, maybe 1/2" long. It's not hard to tell where it went. Just look at the top of the piston. :(
The damage to the piston seems to be superficial. I used to be a general line mechanic for a Ford dealer and before that I was building air cooled VW engines for fun and profit. I told the mechanic to put the new head on it and we'd run it until it blows up, then look for a whole engine.
It may last for years, it may not make it out of the driveway. But I've seen worse looking pistons that hadn't given any trouble. It's a chance I'm willing to take. It's really a no-lose situation. I either need a new engine now, or I'll need one later. The switchover cost will be the same either way. I've already bought the head and I can't take it back. If I get another year or two out of this engine, that's another year or two I have to find another if I need it. If it outlasts the rest of the car, great. If it lasts long enough that the car isn't worth fixing, that's a plus too.
-- Jack
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