I stuck this in the MK indy section because this issue was discussed in there! I pasted it in here for other zetec users on request!So here it is....
May I just place a warning here...the exhaust question seems to have gone 2 ways...one of which was about zetecs!
The warning is this: over here in holland several zetecs were sold as surplus Ford Germany stock to people in our seven club. Every single one has broken down cracked heads, broken conrods you name it!
I exchanged a cvh in my w***field for one of these "new" zetecs and ran it for about 3000km's before one piston fried away to the rings and other cylinders had large scratches on them.
Now this may not happen to you ! but i would go for a secondhand engine you know has been scrapped because of a car accident. Play save and make very sure these engines are good....a good hint is that on our engines there were no engine numbers!
A couple of tips for using a zetec are the following:
1. using an escort 1800 sump gives 2.5cm more clearance than a 2.0L sump. It fits the wrong way round with no problems.Have a look at my homepage for pictures.
2.Why not use a Daihatsu charade alternator instead of the heavy Ford lump.They are the same make and model as demon tweeks sell for 186 pounds. Compare the catalog with the pictures on my site
3. The waterpump needed is the one from the 1800 ESCORT.If you use one from the 1.8 or 2.0L Mondeo they will turn the wrong way! Again see pictures of the difference on my site.
I'll stick them in the photo section aswell.
Good luck with buying and using a zetec.

Siert,

Holland.

i agree with hicost there unless you have a coolant circulation problem caused by a non standard instilation

Agreed, after all if it did 3000km I doubt there was much wrong with the original mechanicals.

Ignition timing probably too far advanced or possibly an air leak from one of the bike carbs.

Yep If damage was restricted to 1 cyl then I too would go down, fueling/airleak/valves/cooling line. Visible bore of adjoining cylinder looks to be ok.