there are many reasons why a non-interference engine can show signs of being an interference engine. like if a if a valve spring were to break which isn't hard to do if the engine is either not well maintained or if the engine is running at high RPMs alot.
besides if we did have an interferance engine with the amount that I have seen timing being off on here most interference engine the valve would of hit the piston in some cases. I recall someones being off my 10 degrees whihc is ALOT and IF it was an interferance engine the pistons would be bye bye in that case. automotive industry has the tightest tolerances in the world most parts are made to a millionth of an inch. which makes 10 degrees seem like a mile.
and from the blue prints of the Zetec I have looked over it is a non-interference design.
