the 250 inline-6 (replaced by the 292 inline-6), 366 V8, and 427 V8. In both Chevrolet and GMC school buses, the Allison AT475 3-speed automatic transmission became an option in 1971 with single or two-speed rear axles. In 1974, the powertrain lineup was modified, as all GMC-built engines were dropped (alongside all diesel engines). In 1980, a diesel engine made its return as Detroit Diesel introduced an 8.2L V8. Dubbed the "Fuel Pincher", it was the first four-stroke engine produced by the company; the engine was available in naturally-aspirated and turbocharged forms. GMC (1966–1970) In 1966, the GMC division moved its school bus chassis from the medium-duty C/K to the all new H6500 heavy truck. A forerunner of both the GMC Brigadier and GMC General, the H-series trucks featured an all-steel front fascia with a center-hinged "butterfly" hood for engine access. Alongside GMC V6 and V8 gasoline engines, GMC school bus chassis were available with Detroit Diesel 6V53 V6 diesels. In 1969, GMC transitioned its medium-duty trucks to the Chevrolet-based C/K medium-duty chassis introduced in 1967. The heavy-duty GMC school bus chassis remained in use by the division for 1970, before both divisions consolidated designs for 1971. Second generation (1984–1991) While General Motors redesigned its entire light and medium-duty C/K truck line for 1973, Chevrolet and GMC retained the previous-generation cowled bus chassis for nearly another decade. For 1984, a second generation was introduced, consolidating conventional trucks and cowled bus chassis for the first time. Codenamed B6, the redesign was again shared by both Chevrolet and GMC, differing only in grille design. From the drivers' compartment, the B6 chassis shared the steering column with its predecessor (with nearly the same instrument panel). In a major design change, the rear-hinged hood was replaced by a standard front-hinged tilting hood, allowing improved engine access. The 6.0L (366) and 7.0L (427) V8 engines made their return, along with the 8.2L Detroit Diesel "Fuel Pincher" V8. In 1990, the 8.2L engine was discontinued. In 1985, General Motors developed a modified version of the B series for Ward Body Works as a chassis for the Ward Patriot school bus. To allow for a shortened hood (to improve driver visibility), the front chassis of the C/K conventional was shortened for a configuration similar to that of the smaller Chevrolet/GMC P-chassis. The "semi-forward control" design would be developed further by GM with the Thomas Vista, another bus