The Buick Straight 6 was an engine manufactured by Buick from 1914–1930 and was exclusively used in the Buick Six platform, then later in the Buick Master Six and Buick Standard Six. They were OHV, like their previous engines, as Buick had been almost exclusively using overhead valve engines since the Model B in 1904. The engine also had the starter and generator in a single unit. The engine did not have a removable cylinder head, meaning the cylinders and valves came off as a unit, (although with the valves in cages, the cages were removable individually), and pistons had to come out of the bottom of the unit as it was removed. They had a displacement ranging from 191 to 331 cu in (3.1 to 5.4 L) depending on year and model. In 1922 the series was divided into the lower priced Standard Six