Actually, BMW started producing cars before WWII, but switched to aircraft engines during the war. They produced their first car in 1928. You are correct though that they produced aircraft engines before they made cars.Well let me further educate you then, BMW was not a car manufacturer until after the end of WWII. BMW manufactured aircraft engines, which were also used in the military in the war. Maybe its the reason the rings, in their engines never last as long as the competitors. In aircraft engines, there are required mandatory rebuilds for safety, which IMHO is probably the reason.
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Their logo represents a propeller blade spinning.