An auto-reconditioner package for in situ reconditioning of worn surfaces of machinery parts under normal running was applied to diesel engines of DF locomotives. A reconditioning layer was generated on the cylinder bore after running a mileage of 300,000 km, and no wear was measured for the piston rings and cylinder bores. Evaluations with SEM, nanohardness tester and XPS indicated that the protective layer assumed a thickness of 8-10 microm, a nano-hardness twice as high as that of the cast iron substrate, and a main elemental composition of Fe, O and C corresponding to the existence of Fe3O4 and Fe3C. A possible formation mechanism of the protective layer was suggested based on the mechanochemical activation of metal surfaces and the catalytic activation of the auto-reconditioner molecules.