History of Issues
While it’s true that thrust bearings operate on only a thin film of oil, they still have trouble supporting as much of a load as radial bearings. Radial bearings can carry loads up to thousands of pounds per square inch, and thrust bearings only handle a few hundred.
Due to the curved surfaces of where the bearing and journal meet, radial types develop a higher load capacity. Thrust bearings are made up of two flat surfaces that come together and no space in order to support oil film formation. The conventional type of thrust bearings are constructed via the incorporation of flanges at the end of a radial journal bearing. They’ve been successful for a long time.
Most shaft surfaces as well as surfaces of thrust bearings and other varieties are flat making it tough to keep a thin film of oil in place. When a thrust load is applied to the crankshaft and oil is squeezed out excessively a bearing failure can occur due to collapsing. This is why a contoured face is important in many applications as it allows thrust washers to be separated and handle higher thrust loads.
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New automatic transmissions have created the need for contoured thrust bearings in order to handle higher loads. This makes sense because it’d be pointless to install contoured faces on single piece flanged thrust bearings. Both flanged bearings and separate thrust washers are a great choice for new engine designs, and they come in a three-piece assembly.
Of course, obvious causes of failure for thrust bearings are improper assembly, dirt and other contaminants. However, there are some other common reasons for failure, they include:
Misalignment – Periodic dressing is necessary to keep the grinding wheel clean and sharp. If it’s not cutting clean it can easily create hot spots. An exact ninety degree dressing to the outside diameter will ensure the thrust feed is slow enough to be effective. Machinists should only remove minimal stock.
Remanufactured options are great, as they don’t require grinding. This is because the grinding wheel won’t even come into contact. Crankshaft end float is usually figured and set before grinding more material from the thrust face.
When it comes to crankshaft grinding wheels, one must realize they are not specifically made for use of the wheel or even for metal removal. Grinding the thrust faces of a crankshaft should only be done by a machinist with attention to detail throughout the entire job. Continual wheel dressings may be necessary and having enough coolant is important to prevent the aforementioned burn spots.
The thrust bearings and surface must be maintained to prevent what is called stone loading as well, and grinding should always end in a what’s called a “spark out.” Again, it’s crucial to maintain a surface of thrust that is 90 degrees in relation to the crankshaft center line.
Bad crankshaft finished surfaces – Thrust faces are hard to grind since they are done using the side of the grinding wheel. Marks left from grinding on the crankshaft makes a swirl pattern and if these scratches aren’t polished off they’ll affect operation adversely, and cause failure.
Overloading – Many factors may contribute to wear and tear, as well as the overloading of a thrust bearing, such as:
1. Improper crankshaft surface finish.
2. Improper crankshaft surface geometry.
3. External overloading, in relation to torque-converter pressure, bad thrust bearing adjustment, riding the clutch pedal, and too much load pressure on the rear crankshaft because of faulty front-mounted drive.