Fiat twin cam engine
The engine was developed under the direction of Aurelio Lampredi , initially as an 8-valve version and later as a 16-valve version. Numerous vehicles of the Fiat group were equipped with the twin-cam engine as standard.
The engine also celebrated success in racing: between 1977 and 1992 it won eleven brand titles in the World Rally Championship , in 1980 and 1981 the Group 5 brand world championship , as well as other titles at national level. The Fiat Twin-Cam engine is the most successful rally engine in history to date.
Later use and further development
All Lampredi engines built up to then had in common that with longitudinal installation the inlet side was on the left in the direction of travel and the exhaust on the right or that with transverse installation, as in the Lancia Beta, the engine was installed inclined 20 degrees backwards against the direction of travel and the inlet to the radiator grille and the outlet was pointing to the bulkhead. The engine was fundamentally redesigned for the first time for use in the Lancia Thema and Fiat Croma. The engine received a new, now one-piece cylinder head without a separately removable camshaft housing, and the installation position was changed so that the engine was inclined 15 degrees forward in the direction of travel - this engine variant was no longer installed lengthways. At the same time, the direction of flow was changed so that the inlet pointed towards the bulkhead and the outlet towards the radiator grille. In addition, the engine block was redesigned so that the use of two balance shafts was possible, which were used in some variants. A one-piece four-valve cylinder head was later developed for this engine, which had nothing to do with the old sports cylinder head and was used in vehicles such as the Lancia Thema 16V, the Fiat Tipo Sedicivalvole, the Lancia Integrale 16V. The last variant built by the Lampredi engine was a four-valve engine with 1.6 liter displacement, which was used in the Fiat Bravo / Brava until 2000.
The engine has four cylinders , an engine block from cast iron with five-bearing crankshaft and a cross-flow - cylinder head made of aluminum with two overhead camshafts. The two camshafts act on the V-shaped valves via bucket tappets and are driven by a toothed belt.
The basis of this engine was the OHV engine of the Fiat 124, which was also developed by Lampredi. The lower camshaft was replaced by a secondary shaft for driving the oil pump and ignition distributor, which was then driven by the toothed belt.
The Lampredi four-cylinder in the originally exclusively manufactured 8-valve version always had a three-part cylinder head: one cast part carries the combustion chamber cap as well as valve guides, valves and springs, two separate parts each carry a camshaft. This construction greatly simplified production compared to other DOHC constructions.
Valve clearance adjustment
The DOHC engine had a new method of valve adjustment, patented for Fiat: the bucket tappets had direct contact with the valves, the spacers necessary to adjust the valve clearance were located at the top of the tappet cups with contact to the camshafts. As a result, the tappet only had to be pressed down with the help of a special tool to adjust the play, the spacer plates could then be removed and inserted with needle-nosed pliers. There was no need to remove the camshafts that had been required in the designs that had been common up until then, such as Jaguar or Alfa Romeo, in order to access the spacer plates on the valves below the tappet cups. This design, which makes maintenance very easy, was also used in the Fiat 128 and laid the foundation for the triumph of OHC and DOHC engines in everyday and high-volume cars. In doing so, she encouraged numerous other companies to circumvent the Fiat patents with their own designs, but ultimately this setting method prevailed until the widespread introduction of hydraulic valve clearance compensators.
Special versions for racing and sports use
In the seventies, a four-valve cylinder head was developed for the Fiat 124 Spider Abarth used in rallying. This was one-piece and had a very narrow valve angle, which is why the camshafts had to be removed to access these screws for the tightening of the cylinder head screws, which was still common at the time during maintenance work. This high level of maintenance was acceptable because the few vehicles equipped in this way were in the hands of the factory sports team and did not end up in the hands of customers. For the later use of the four-valve Lampredi engine in the Fiat 131 Abarth Rally, this cylinder head was revised and provided with a larger valve angle to enable the cylinder head bolts to be retightened without dismantling the camshafts. This change was introduced because the 400 built vehicles of this type also ended up in the hands of customers and the customer did not want to expect high maintenance costs. This engine was then equipped with a supercharger, also used in the Lancia Rally 037.