Breaking in is usually meant as a short period of the running of the machinery under no load to achieve maximum wear rate, so that asperities break faster. In the case of piston rings, this is so that the piston rings are allowed to seat and lubricate properly. The breaking-in time may differ from engine to engine and is provided in the engine manual by the makers and an average breaking-in time for a four stroke engine is 48 hours. The term "Run-In" is usually used to describe the initial period of time or operation where the machine is run at light load, as described in the engine builders instructions or in the Owner's Manual. This question is about the role valleys play in the cylinder bore and is a multiple choice question. Please select the best answer. A, The valleys provide for oil storage B. Valleys provide a reservoir for early wear debris to keep the debris from agglomerating and causing subsequent scuffing C. Because of the rough surface, plastic deformation occurs in order to speed up tribofilm formation. D. All of the above. This question is not open to tribologists, chemists, formulators, or any engineering discipline.