Volkswagen (VW) manufactured its air-cooled engine from 1936 until 2003. During that time, the German carmaker used the engine in four types of its vehicles but most commonly in its Beetle, Bus and 1500/1600. VW also employed the air-cooled technology in industrial and aircraft settings, as well as in kit cars.
VW introduced its air-cooled engines in 1936. In these engines, unlike the more common water-cooled engines, the fan pushes air through the back window. The air travels over the cylinders and cylinder heads before metal ducting turns it and guides it out of the rear of the vehicle.
Three types of VW vehicles featured the air-cooled engine --- types 1 through 3. Volkswagen introduced the Type 1, more commonly referred to as the Beetle, in 1938. It began making its panel van --- the Type 2, also called the Bus or Transporter --- in 1950. The Type 3 is the lesser-known 1500 or 1600 model vehicle. Volkswagen manufactured this compact car from 1961 until 1973.
VW offered multiple engines in these vehicles over the years. In Beetles, the available engines displaced 1.2, 1.3, 1.5 or 1.6 litres. They could produce between 36 and 65 horsepower. Type 2 vehicles' engines displaced 1.2, 1.5, 1.6, 1.7, 1.8, or 2 litres and produced 36 to 57 horsepower. Type 3 air-cooled VW vehicles had engines that displaced 1.5 or 1.6 litres and produced 54 to 65 horsepower.
In air-cooled VW engines, the connecting rod bolts require between 22 and 25 foot-lbs. of torque. While the original VW specifications indicate that the studs for the crankcase halves require 25 foot-lbs. of torque, most engine rebuilders use 30 foot-lbs. of torque for the 10mm studs and 18 foot-lbs. of torque for the 8mm studs. The four small nuts for the crankcase halves require 14 foot-lbs. of torque. The cylinder head nuts receive 23 foot-lbs. of torque, and the engine mounting bolts require 22 foot-lbs. of torque. The oil drain plug requires 25 foot-lbs. of torque. The spark plugs attach to the head with torque levels ranging from 22 to 29 foot-lbs.