The mk3 Escort was available with two sizes of the OHV (Over Head Valve) engine, 1.1ltr and 1.3ltr. This is a pushrod engine (as opposed to an overhead cam engine) and both sizes shared the same bore size, the extra displacement of the 1.3 being achieved by using a longer stroke crankshaft. The larger 1.3 also used a five main bearing crank whereas the smaller 1.1 used a three main bearing crank
It is basically the same OHV engine as was fitted to earlier rear wheel drive (RWD) Escorts, some Cortina's and the Fiesta. In fact it's descendent saw use as the 'Valencia' in the Ford Ka.
The earlier Escort and Cortina OHV engines will not fit the front wheel drive mk3 Escort (or Fiesta) as the blocks are slightly different. This is due to the front wheel drive Escorts transverse engine mounting. The later FWD blocks have a mounting bolster incorporated into the block near the crank shaft pulley end to accommodate the right hand engine mount. Due to the inline configuration of the earlier RWD cars, this mounting point does not exist.
In 1986, with the introduction of the mk4 Escort, revisions were made to the two OHV engines. The valve timing was changed on both to give shorter opening durations to both inlet and exhaust valves and the 1.1 ltr engine had it's valves reduced in size. Keep this in mind when sourcing parts from mk4 cars down the breakers as the camshafts will be different to give the smaller cam duration and although the parts will probably fit (I haven't try'd it myself) you will loose performance.
The OHV engine was fitted to the mk4 Escort up until 1989 when it was replaced with the High Compression Swirl (HCS) engine. This is a lean burn development of the OHV engine and although it is similar in appearance and construction to the OHV engine there are a number of changes involved. The main difference is in the design of the cylinder head.
The inlet ports and combustion chamber have been redesigned to induce a high degree of swirl into the incoming gas flow as it enters the chamber to give improved mixing. The inlet and exhaust ports and valves have also been moved around. They now adopt a mirrored arrangement where by the two centre cylinders (2&3) now have there inlet valves next to each other. This means that the inlet and exhaust manifolds from the HCS engine will not fit the OHV engine as the ports will not match up. It also means that the camshaft cannot be swapped either as the inlet and exhaust valve lobes will be in the wrong positions.
Another new feature of the HCS engine was the adoption of a solid state ignition system. Instead of a conventional distributor, the HCS engine uses Fords DIS (Distributor-less Ignition System) system. This is a simple computer controlled ignition system that uses three sensors on the engine to determine when and where to fire a spark.
Finally, the HCS engine also uses a different carburetor to account for the differing fueling characteristics
Other than those differences mentioned, the HCS engine can be regarded in the same way as the OHV engine.
