Buick V6 Engine - Fireball V6

Fireball V6

The first engine in this family was introduced in 1961 for the 1962 model year Buick Special with Buick's 198 cu in (3.2 L) engine, the first V6 in an American car. Because it was derived from Buick's 215 cu in (3.5 L) aluminum V8, it has a 90° bank between cylinders and an uneven firing pattern due to the crankshaft having only three crank pins set at 120° apart, with opposing cylinders (1-2, 3-4 and 5-6) sharing a crank pin in, as do many V8 engines. The uneven firing pattern was often perceived as roughness, leading a former American Motors executive to crow "It was rougher than a cob."

In 1977, Buick redesigned the crankshaft to a "split-pin" configuration to create an "even-firing" version. The crank pins associated with the opposing cylinders were offset from each other by 30°. The relatively small offset did not require flying arms to be incorporated, however a 3.0 mm thick flange was built in between the offset crank pins to prevent the connecting rod big-ends from "walking" off the crank pin bearing journal and interfering with the adjacent big end. The 3.0 mm thick flange effectively caused the connecting rods on the left-hand bank of cylinders (forward bank for FWD applications) to move 3.0 mm forward relative to the right-hand bank, but the engine block remained unchanged compared to the odd-fire engine. Since the cylinders centre-lines were no longer centralised over the crank pin bearing journals, the connecting rods were re-designed with the big-ends offset from the piston pin ends by 1.5 mm. The engine in this configuration became known to have "off-centre bore spacing".

The off-centre design continued up until the 1988 LN3 version of the engine, when the left-hand bank of cylinders was moved forward relative to the right-hand bank. Although the actual bore spacing between cylinders on the same bank remained unchanged at 107.7 mm (4.240"), the LN3 and later engines became known to have "on-centre bore spacing".