Cylinder Block, Seven Main Bearings & Mounts

The foundation of the 4.9L (300 CID) inline-six is its deep-skirt gray cast-iron cylinder block. Its side walls extend well below the crankshaft centerline, and seven cast-iron main bearing caps—one between every cylinder—clamp the crankshaft into the block saddle.

This group also includes the upper and lower plain main bearing shells, the flanged #5 thrust bearing pair that controls crankshaft fore-and-aft endplay, brass core plugs, oil gallery plugs, the steel block-to-bellhousing rear alignment plate, and the LH/RH rubber-isolated frame engine mounts.

Seven-Main-Bearing Load Path: Many inline-sixes made do with four main bearings, leaving two connecting rods sharing unsupported spans. Ford gave the 300 inline-six seven main journals so every firing pulse is immediately absorbed by two adjacent main caps.

Axial Thrust Control at Journal #5: Whenever you step on the clutch pedal, the concentric slave cylinder pushes forward with hundreds of pounds of force through the pressure plate and flywheel into the crankshaft. The #5 main bearing shell has integral 360-degree bronze-faced side flanges that absorb that axial load against machined thrust faces on the crank web.