60411 Mariner SCREW (.312-18 X 1.25)

Illustration 1 g00582045
Left side of engine
(1) Camshaft covers
(2) Crankcase coversCamshaft covers (1) allow access to the camshaft and valve lifters. Crankcase covers (2) allow access to the crankshaft connecting rods, main bearings, and piston cooling jets. When the covers are removed, all the openings can be used for inspection and service.Pistons, Rings And Connecting Rods
The piston is a two-piece, articulated design. The piston consists of a forged, steel crown and a cast, aluminum skirt. The two pieces of the piston assembly are connected to the piston pin. The two pieces of the piston assembly pivot about the piston pin. The steel crown carries all three piston rings. Oil from the piston cooling jets flows through a chamber which is located directly behind the rings. The oil cools the piston which improves the life of the rings. The pistons have three rings which include two compression rings and one oil ring. All the rings are located above the piston pin bore. The oil ring is a standard ring. Oil returns to the crankcase through holes in the oil ring groove. The top two rings are the Keystone rings, which are tapered.The connecting rod has a taper on the pin bore end. This taper gives the rod and the piston more strength in the areas with the most load. Four bolts, which are set at a small angle, hold the rod cap to the rod. This design keeps the rod width to a minimum, so that a larger rod bearing can be used and the rod can still be removed through the liner.Crankshaft
The crankshaft changes the combustion forces in the cylinder into usable rotating torque which powers the machine. A vibration damper is used at the front of the crankshaft in order to reduce torsional vibrations (twist) that can cause damage to the engine.The crankshaft drives a group of gears on the front and the rear of the engine. The gear group on the front of the engine drives the oil pump, the jacket water pump, the fuel transfer pump, and the accessory drives.The rear gear group, which is also driven by the crankshaft, drives the camshafts and the accessory drives.Seals and wear sleeves are used at both ends of the crankshaft. The seals and wear sleeves are used for easy replacement and reduction of maintenance cost. Pressure oil is supplied to all main bearings through drilled holes in the webs of the cylinder block. The oil then flows through drilled holes in the crankshaft in order to provide oil to the connecting rod bearings. The 3512B crankshaft is held in place by seven main bearings. A thrust plate at either side of the center main bearing controls the end play of the crankshaft.Camshaft
There is one camshaft per side. The 3512B camshaft is supported by seven bearings. Each camshaft is driven by the gears at the rear of the engine.As the camshaft turns, each lobe moves a lifter assembly. There are three lifter assemblies for each cylinder. Each outside lifter assembly moves a pushrod and two valves. The valves can be inlet valves or exhaust valves. The center lifter assembly moves a pushrod that operates the fuel injector. The camshafts must be in time with the crankshaft. The relation of the camshaft lobes to the crankshaft position causes the valves and fuel injectors in each cylinder to operate at the correct time.