Here's another interesting application of sealed bearings in an externally lubricated application, although it's with hot oil instead of grease - the 2001-2007 KTM "RFS" engine (used in 400/450/525 dirt bikes and other applications) use roller bearings on the cam shaft in the cylinder head. These motors use oil spray lubrication in the head and run up to 10,000 rpm.
Originally in the first couple years of production, these roller bearings were the open or shielded style, which made sense in the oil lubricated environment. However, high rpm roller bearings don't tolerate even minute flecks of metal or carbon grit, so the bearings were prone to failing as the engine started to wear. KTM switched to sealed bearings and eliminated the failures. Apparently enough oil gets by the seals to keep the bearing lubricated, and they generally last the life of the engine with no issues.
Originally in the first couple years of production, these roller bearings were the open or shielded style, which made sense in the oil lubricated environment. However, high rpm roller bearings don't tolerate even minute flecks of metal or carbon grit, so the bearings were prone to failing as the engine started to wear. KTM switched to sealed bearings and eliminated the failures. Apparently enough oil gets by the seals to keep the bearing lubricated, and they generally last the life of the engine with no issues.
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