Are they connected with the main bearings? Are the trust bearings only on the outer portions of the crankshaft?
The thrust BEARING (there is only one) is part of the transmission. It's separate from the main bearings of the engine.
My 4-cylinder has a total of four thrust bearing parts. They set next to one of the main bearings. There are two upper and two lower pieces so it takes a total of four. Yes they can be a problem as the two lower ones have a tendency to slip out of place and fall into the oil pan as they near the end of their useful life. But most 4-cylinders have a single thrust bearing built into one of the main bearings so they are not separate parts.
It all really depends on the application. But usually there is only one set of thrust bearings, and they are usually formed as part of the center main bearings. Sometimes they may be on the outer two mains, but they are almost always part of the main bearings.
