Posted: Mon May 02, 2005 9:31 pm
More info here
http://www.babcox.com/editorial/ar/ar20128.htm
But this should clear up any problems
Bearing wear
As an engine accumulates miles, the crankshaft and camshaft bearings eventually become worn and need to be replaced. That’s why engines have bearing inserts — so the worn surfaces can be restored by simply replacing the bearings. If there were no bearing inserts, every worn surface would have to be remachined or replaced. Imagine how expensive that would be!
Most bearing wear occurs immediately after a cold start because there’s little or no oil film between the bearing and shaft. As the shaft begins to rotate, it turns against the bearing and attempts to climb the bearing wall until there’s enough oil pressure to form a wedge of oil underneath the shaft. This separates the shaft from the bearing and allows it to float on a thin film of oil much like a bald tire hydroplaning across a puddle of water. This eliminates metal-to-metal contact and wear, and cuts friction to almost nothing.
As long as the shaft is supported by the thin film of oil, bearing and shaft wear is virtually nil. But under high loads and high rpms, the oil film can be squeezed down to almost nothing. Under such conditions, metal-to-metal contact can occur causing wiping and wear. To counteract this danger, zinc dithiophosphate is used as an additive in motor oil to provide "boundary lubrication" when the oil film is too thin to provide normal protection. However, even this may not be enough under severe operating conditions (such as racing or hard driving) to protect the bearings.
Bearing wear can also occur if contaminants find their way into the bearing via the oil supply. The oil filter will usually trap most particles large enough to cause problems, but if the filter is not maintained properly and becomes plugged, unfiltered oil can bypass the filter and carry contaminants directly to the bearings. The main bearings will usually suffer the most because they’re the closest to the oil pump and the first to receive oil.
Most bearings provide a certain amount of "embedability" which is the ability to absorb small particles of debris into the surface of the bearing. Embedability depends on the hardness of the bearing surface, and the depth of the surface layer. The softer the bearing alloy and the deeper the top layer, the more easily the bearing can handle contaminants that are too large to flush out.
If a particle is too large to be flushed out of the space between the bearing and shaft, and becomes embedded in the surface of the bearing, it can score and damage the shaft journal if it protrudes above the surface of the bearing. It will act like a cutting tool and scrape away at the shaft journal until one or both wear down. Embedded particles can also breakup the oil film causing a localized hot spot on the bearing that can lead to bearing failure.
Oil breakdown is another condition that can cause bearing wear or failure. Severe overheating can cause the oil to burn (oxidation) resulting in a breakdown of the lubricant. Maintenance neglect (not changing the oil and filter often enough) can also allow a build-up of sludge and contaminants in the crankcase which will accelerate bearing wear and increase the risk of bearing seizure and failure.
Dilution of the oil with raw fuel (from piston blowby or an overly rich fuel condition) can also break down the lubricant and cause the bearings to fail. The underlying problem may be a misadjusted carburetor float or choke, leaky injectors or a plugged or defective PCV system or valve.
Oil contamination by antifreeze is another problem that can wipe out a set of bearings. Antifreeze can enter the crankcase through a defective head gasket, a poor seal between the head and block (usually the result of undetected head or deck warpage, improper head resurfacing, loss of head bolt torque or head gasket leaks) or through cracks in the head or block water jackets.
Anything that causes a drop or loss of oil pressure can also prove fatal for the bearings. This includes oil leaks that lead to a low oil level in the crankcase, a worn or broken oil pump, an obstructed oil pickup screen or tube, or an oil galley plug that blows out under pressure.
http://www.babcox.com/editorial/ar/ar20128.htm
But this should clear up any problems
Bearing wear
As an engine accumulates miles, the crankshaft and camshaft bearings eventually become worn and need to be replaced. That’s why engines have bearing inserts — so the worn surfaces can be restored by simply replacing the bearings. If there were no bearing inserts, every worn surface would have to be remachined or replaced. Imagine how expensive that would be!
Most bearing wear occurs immediately after a cold start because there’s little or no oil film between the bearing and shaft. As the shaft begins to rotate, it turns against the bearing and attempts to climb the bearing wall until there’s enough oil pressure to form a wedge of oil underneath the shaft. This separates the shaft from the bearing and allows it to float on a thin film of oil much like a bald tire hydroplaning across a puddle of water. This eliminates metal-to-metal contact and wear, and cuts friction to almost nothing.
As long as the shaft is supported by the thin film of oil, bearing and shaft wear is virtually nil. But under high loads and high rpms, the oil film can be squeezed down to almost nothing. Under such conditions, metal-to-metal contact can occur causing wiping and wear. To counteract this danger, zinc dithiophosphate is used as an additive in motor oil to provide "boundary lubrication" when the oil film is too thin to provide normal protection. However, even this may not be enough under severe operating conditions (such as racing or hard driving) to protect the bearings.
Bearing wear can also occur if contaminants find their way into the bearing via the oil supply. The oil filter will usually trap most particles large enough to cause problems, but if the filter is not maintained properly and becomes plugged, unfiltered oil can bypass the filter and carry contaminants directly to the bearings. The main bearings will usually suffer the most because they’re the closest to the oil pump and the first to receive oil.
Most bearings provide a certain amount of "embedability" which is the ability to absorb small particles of debris into the surface of the bearing. Embedability depends on the hardness of the bearing surface, and the depth of the surface layer. The softer the bearing alloy and the deeper the top layer, the more easily the bearing can handle contaminants that are too large to flush out.
If a particle is too large to be flushed out of the space between the bearing and shaft, and becomes embedded in the surface of the bearing, it can score and damage the shaft journal if it protrudes above the surface of the bearing. It will act like a cutting tool and scrape away at the shaft journal until one or both wear down. Embedded particles can also breakup the oil film causing a localized hot spot on the bearing that can lead to bearing failure.
Oil breakdown is another condition that can cause bearing wear or failure. Severe overheating can cause the oil to burn (oxidation) resulting in a breakdown of the lubricant. Maintenance neglect (not changing the oil and filter often enough) can also allow a build-up of sludge and contaminants in the crankcase which will accelerate bearing wear and increase the risk of bearing seizure and failure.
Dilution of the oil with raw fuel (from piston blowby or an overly rich fuel condition) can also break down the lubricant and cause the bearings to fail. The underlying problem may be a misadjusted carburetor float or choke, leaky injectors or a plugged or defective PCV system or valve.
Oil contamination by antifreeze is another problem that can wipe out a set of bearings. Antifreeze can enter the crankcase through a defective head gasket, a poor seal between the head and block (usually the result of undetected head or deck warpage, improper head resurfacing, loss of head bolt torque or head gasket leaks) or through cracks in the head or block water jackets.
Anything that causes a drop or loss of oil pressure can also prove fatal for the bearings. This includes oil leaks that lead to a low oil level in the crankcase, a worn or broken oil pump, an obstructed oil pickup screen or tube, or an oil galley plug that blows out under pressure.
