2. Bearing failure occurs due to insufficient lubrication, excess dirt and foreign matter in the oil, engine overload or corrosion (see picture).
Figure 17.2. Typical damage to bearings.
Regardless of the cause of bearing failure, it must be corrected before engine assembly to prevent it from happening again.
3. To inspect the liners, remove them from the engine by dismantling the main and connecting rod bearing caps/block. Lay the liners out on a clean horizontal surface in the order they are located on the engine. This will make it possible to match the bearing problems with the corresponding cylinders. The inserts require delicate handling - their working surfaces can be easily scratched even by fingers.
4. Dirt and other foreign particles enter the engine in different ways. They may remain in the engine after assembly or penetrate through filters or crankcase ventilation. They can get into the oil and with it into the bearings. Metallic particles, which are products of normal wear or mechanical processing of parts, are often present in oil. Abrasives often remain in the engine after its repair, especially if the engine was not properly flushed after treatment. Regardless of the source, these foreign particles often end up embedded in the soft metal of the bearings, where they are easily recognized. Large particles will leave scratches on both the neck and the liner. The best cure for these ailments is cleanliness - wash all engine components thoroughly and keep everything spotlessly clean during assembly. Frequent and regular oil and filter changes are also recommended.
5. Oil "fasting" (or cessation of lubrication supply) has many interconnected causes. Elevated temperature (the oil becomes unacceptably liquid), overload (squeezes grease out of plain bearings), oil leakage through increased clearances in bearings, a worn oil pump, and high engine speeds can cause lubrication to stop. Lubrication channels clogged with dirt and narrowing of the channels due to misalignment of the oil passage holes in the bearing shells cause oil starvation of the bearings and premature failure. If a lack of lubrication is the cause of bearing failure, the soft material of the plain bearing will wear away from the metal substrate until it is completely removed. Increased friction temperature will color the bearing pad in tarnished colors.
6. The lifespan of the liners is greatly affected by driving style. Full throttle ("pedal to the floor", "full hole"), driving "under tension" create large loads on the crankshaft bearings, squeezing the oil film out of their gaps. These loads weaken the liners, leaving fatigue microcracks in their working surfaces. The cracked material comes off the substrate in pieces.
7. Short-distance driving leads to bearing corrosion because condensation and corrosive gases are not removed from the unheated engine oil and form acid and sludge in it. All this is supplied together with oil to the plain bearings.
8. Incorrect installation of bearings naturally leads to their wear. Overtightened bearings have insufficient clearances, insufficient clearances have insufficient lubrication. Dirt and foreign matter clog the insufficient clearances, leaving the bearings without lubrication.
9. When assembling, try not to touch the working surfaces of the liners, as they can easily be scratched or left with dirt. The earbuds can only be wiped with a clean, lint-free cloth.
10. As already noted, saving on replacing bearing liners can result in a repeat overhaul of the engine.