Q. What does 'B-50' mean in terms of engine life?
A. Engine life is defined as miles until the first in-frame overhaul is required.
B50 life (in miles) means that half (50%) of the engines built will need to have an in-frame overhaul completed by this mileage. Cummins ISX engines have a B50 life of greater than 1 million miles, for instance, so 50% will need an in-frame overhaul before 1 million miles, and 50% will need an in-frame overhaul after 1 million miles.
The term "B XX" was actually created by the ball bearing industry during World War Two to classify how long their ball bearings would run. The term has been carried over to the current heavy-duty diesel engine business.