GMC straight-6 engine

The GMC straight-6 engine was a family of gasoline-powered inline six-cylinder engines that the GMC Trucks division of General Motors introduced in the 1939 model year. Until then GMC trucks had used straight-six engines designed by the Buick, Pontiac and Oldsmobile divisions. The new family used a valve-in-head layout that Buick had pioneered and that Chevrolet also used in its Stovebolt Six, and it was built in many displacements on three block sizes that the article calls Group 1, Group 2 and Group 3. The Group 1 engines were the smallest and had four main bearings, while the larger groups had seven. Sizes ran from the 228 cubic inch engine up to the 503 cubic inch engine, and a sealed 302 cubic inch version went into military trucks. The GMC V6 engine replaced the straight-six in 1960, and it survived only in certain light-duty P-series step vans until 1962.