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A crankpin or crank pin, also known as a rod bearing journal, [1] is a mechanical device in an engine which connects the crankshaft to the connecting rod for each cylinder. It has a cylindrical surface, to allow the crankpin to rotate relative to the "big end" of the connecting rod.
This block is one of three displacements, 302/327/350, that underwent a crankshaft bearing diameter transformation for 1968 when the rod-journal size was increased from the 2 in (50.8 mm) diameter small-journal to a 2.1 in (53.3 mm) large-journal and a main-journal size that was increased from 2.3 in (58.4 mm) to 2.45 in (62.2 mm).
The crankshaft stroke and main journal size changed among the years with the more popular 389CI and 400CI having a 3.00" diameter main journal and the 421/428/455 sharing a larger 3.25" diameter main journal. The V8 was phased out in 1981, replaced by GM "corporate engines" such as the Chevrolet 305 cu in small block V8.
This higher pressure is developed by the relative speeds in feet per second (not RPM or journal size directly) of the crankshaft journal itself against the bearing, the bearing width (to the closest pressure leak), oil viscosity, and temperature, balanced against the bearing clearance (the leakage rate).
The number of main bearings is primarily determined by the overall load factor and maximum engine speed. [1] Increasing the number of bearings in an engine will generally increase the size and cost of the engine, but also reduces bending stress and deflection caused by the distance from the crank pins to the nearest bearings.
The 4.3 L (262 cu in) V6 has a 4 in × 3.48 in (101.6 mm × 88.4 mm) bore and stroke, identical to the 350 cu in (5.7 L) Chevrolet V8 engine. To create a true even-fire engine, Chevrolet produced a crankshaft with 30-degree offsets between each rod pin. Consequently, rod journals were increased to a larger 2 + 1 ⁄ 4 inches
The simplest solution, as used in most road car engines, is for each pair of cylinders to share a crank journal, but this reduces the size of the rod bearings and means that matching (i.e. opposite) cylinders in the different banks are slightly offset along the crankshaft axis (which creates a rocking couple). Another solution is to use master ...
The major differences of the 350 in comparison to other GM V8s are Buick's "deep-skirt" engine block construction, the use of cast iron with increased nickel content, under-square cylinder bore sizing, 3 in (76.2 mm) crankshaft main journals, and 6.385 in (162.2 mm) connecting rods. Of all the GM "350s", the Buick has the longest piston stroke.