Oil Slinger
As an engine runs, the oil gets dirty. The dirt comes from different sources, some is airborne and makes its way past the air filter, some comes from the combustion chamber as byproduct of burning fuel, some comes from the engine itself as it slowly wears over time. In order to lubricate properly, the oil needs to have this dirt removed.
Back in the day of classic motorcycles, there were many clever solutions to cleaning the engine oil that didn't include an oil filter. BMW's solution was to use an oil slinger. The engine oil is routed over a spinning disk with a groove at the outer edge (the slinger). As the engine turns centrifugal force captures the dirt which is heavier than the oil in the groove of the slinger.
Over time, the slinger groove packs full of dirt, gunk, and metal chips. When the slinger groove is full, the engine has absolutely no oil filtration! Your oil has become a vehicle to spread abrasive powder over every bearing surface of your vintage engine's innards! This is not good, in fact it is very bad...
Your classic BMW motorcycle requires a regularly scheduled engine tear-down to clean the oil slinger. The recommended frequency is every 50,000 miles.
