Plastigage brand rod used to measure clearances in main and connecting rod bearings
Measuring the width of a Plastigage rod with a scale to determine the gap size
With proper maintenance and regular oil and filter changes, bearings will last a very long time. A sign of damage to connecting rod bearings is a regular, rhythmic, loud knocking noise from the crankshaft. The frequency depends on engine speed. This knocking noise is especially noticeable when the engine is under load. This sign is accompanied by a drop in oil pressure, although this is usually unnoticeable unless an oil pressure sensor is installed. Damage to the main bearing is usually indicated by noticeable vibration, especially at high engine speeds, and this vibration is accompanied by a more significant drop in oil pressure and a "rumbling" noise.
Bearing liners in good condition have a smooth surface and a uniform matte silver-gray color over the entire surface. Worn liners have areas with different colors where the metal has worn out and the substrate has become visible. Damaged liners have scratches or burrs. If the crankshaft itself is in good condition, then the problem can be easily solved by purchasing another set of bearings of the same size. If the crankshaft is being reground or replaced, the bearing liners must also be replaced during this operation.
The original crankshaft in the cylinder block can have a standard or first repair size, in the latter case this is indicated by the bearing caps, which are marked with white paint.
On 2.8 dm³ engines, both main journals and connecting rod bearing journals have only standard dimensions.
The existing clearance in the bearings can be checked using a proprietary tool, Plastigage rods. A section of Plastigage rod is placed on the crankshaft journal, then the bearing shell and cover are assembled, the bolts and nuts are tightened to the torque specified in subsection 3.3.1. After removing the cover, the width of the rod is measured with a scale ruler, which indicates the size of the gap at that moment.
The text was obtained in its entirety from the specified website (FORDBOOK.ru)