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The large-journal connecting rods were thicker (heavier) and used 3 ⁄ 8 in (9.5 mm) diameter cap-bolts to replace the small-journal's 11/32. 1968 blocks were made in 2-bolt and 4-bolt versions with the 4-bolt center-three main caps each fastened by two additional bolts which were supported by the addition of thicker crankcase main-web bulkheads.
The engine block had 4.84-inch (123 mm) bore centers, two-bolt main bearing caps, a "side oiling" lubrication system (the main oil gallery located low on the driver's side of the crankcase), with full-flow oil filter, and interchangeable cylinder heads. Heads used on the high performance 409 and 427 engines had larger ports and valves than ...
The lower half of the main bearings are typically held in place by 'bearing caps' which are secured to the engine block using bolts. The basic arrangement is for each bearing cap to have two bolts, but some engines may have four or six bolts per bearing cap (often referred to as "four-bolt mains" or "six-bolt mains" engines).
This was the beginning of factory supplied performance items such as 4 bolt main bearings and windage trays to reduce friction from crankcase oil. The 389 would remain the standard Pontiac V8 engine through 1966, offered in a bewildering variety of outputs ranging from 215 to 368 hp (160 to 274 kW).
ASTM A325 is an ASTM International standard for heavy hex structural bolts, titled Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. It defines mechanical properties for bolts that range from 1 ⁄ 2 to 1 + 1 ⁄ 2 inches (13 to 38 mm) in diameter.
On a screw, the bearing area loosely refers to the underside of the head. [1] Strictly speaking, the bearing area refers to the area of the screw head that directly bears on the part being fastened. [2] For a cylindrical bearing, it is the projected area perpendicular to the applied force. [3]
The 351W had larger main bearing caps, thicker and longer connecting rods, and a distinct firing order (1-3-7-2-6-5-4-8 versus the usual 1-5-4-2-6-3-7-8, a means to move the unacceptable "noise" of the consecutively-firing adjacent front cylinders to the sturdier rear part of the engine block all while reducing excessive main bearing load ...
Illustration of bearing tolerances (in micrometers) for a bearing with a 20 mm inner diameter. For illustration, the figure shows the differences in tolerance per ABEC class in micrometers (μm) for a 20 mm inner diameter bearing. [1] A 20 mm ABEC 7 bearing only has a 5 μm tolerance window, whereas an ABEC 1 has twice as wide a tolerance.