The Volkswagen engine is a flat four cylinder design. This four cycle, overhead valve engine has two pairs of horizontally opposed cylinders. All rear engined VW models are air cooled.
The Type 1 and 2/1600 engine is known as an upright fan engine, that is, the engine cooling fan is mounted vertically on top of the engine and is driven by the generator shaft. The Type 2/1700, Type 2/1800, Type 2/2000, Type 3 and 4 engine, although of the same basic design, i.e. flat four, has the cooling fan driven by the crankshaft and is therefore mounted on the front of the engine. This type of engine is known as the suitcase engine.
Because it is air cooled, the VW engine is slightly noisier than a water cooled engine. This is due to the lack of water jacketing around the cylinders which provides sound deadening on water cooled engines. In addition, air cooled engines tend to run at somewhat higher temperatures, necessitating larger operating clearances to allow more room for the expansion of the parts. These larger operating clearances cause an increase in noise level over a water cooled engine.
The crankshaft of all Volkswagen engines is mounted in a two piece crankcase. The halves are machined to very close tolerances and line bored as a pair and, therefore, should always be replaced in pairs. When fitting them, it is necessary to coat only the mating surfaces with sealing compound and tighten them down to the correct torque. No gasket is used.
The pistons and cylinders are identical on any particular engine. However, it is not possible to interchange pistons and cylinders between engines. The four pistons each have three rings, two compression rings and one oil scraper. Each piston is attached to its connecting rod with a fully floating piston pin.
Each pair of cylinders shares a detachable cylinder head made of light aluminum alloy casting. The cylinder head contains the valves for both cylinders. Shrunk-in valve guides and valve seats are used.
Complete engine rebuilding procedures are given in the second half of this section.