mitsubishi 4d55

The Mitsubishi Astron or 4G5/4D5 engine, is a series of straight-four internal combustion engines first built by Mitsubishi Motors in 1972. Engine displacement ranged from 1. 8 to 2. 6 litres, making it one of the largest four-cylinder engines of its time.
It employed a hemispherical cylinder head, chain-driven single overhead camshaft and eight valves. United States passenger car versions had a small secondary intake valve referred to as the "Jet Valve". This valve induced swirl in the intake charge, enabling the use of leaner fuel/air mixtures for lower emissions. It was designed as a cartridge containing the valve spring and seat which simply screwed into a threaded hole in the head, similar to a spark plug but inside the cam cover. The rocker arms for the intake valve were widened on the valve end to accommodate the cartridge, which was equipped with a very soft valve spring in order to avoid wear on the camshaft intake lobe. Modifications to the head were thereby reduced as the Jet Valve negated the necessity for a three-valve-per-cylinder design....