The Zetec comes in a few different flavours as it was developed during it's production run. The engine being referenced to and fitted in this guide is the common Zetec-E. This is the standard Zetec engine fitted to most Escorts and Mondeos of the 90's. There are some minor differences to some of the parts between Escort sourced Zetecs and Mondeo sourced Zetecs that are covered later in this guide.
Pre '94 engines apparently suffered from sticking valves due to a shoulder formed in the valve stem during manufacture fouling on the valve guide. Most engines should however have been rectified by now.

Later engines from the Focus are very similar and the induction system is interchangeable but they aren't ideal when being transplanted into a front wheel drive Escort or Fiesta as they use a new block design resulting in a physically longer engine. They also use smaller width main bearings and so may not be as strong as the original engines.