1 A common trouble with the fuel pump plungers or fuel valve spindles is oil leakage . Good strainers and fine filters should be provided in the fuel oil system and they should be cleaned at intervals, so as to prevent dirt from getting under a fuel injection pump valve and causing it to leak. 2 It is not uncommon for the lubricating oil pump suction to be clogged with the dirt left in the crankcase after work has been done on the engine . Excessive clearances in the main or crankpin bearings will sometimes be indicated by loss of pressure in the lubricating system before any bearing knock is heard. 3 The engine may lose power or slow down when running. When this occurs, the first cause possible may be hot bearings and seizure of the pistons in the cylinders. Failure of the fuel supply to one or more cylinders may be another cause . Cracks in the cylinders and cylinder covers may result from unequal heating. 4 Bearing knocks are likely to occur from bearing wear. Valve gear knocks ate more easily located while the engine is running. nocking that occurs between cams and rollers may be caused by troubles such as excessive clearances and wornor broken rollers, or the trouble may be in the valves.