0284103 JOHNSON ENGINE COVER ASSY., 225PL

Cylinder Head Assembly
The cylinder head is a one-piece cast iron head. The cylinder head supports the camshaft. This improves the rigidity of the valve train. Steel reinforced aluminum bearings are pressed into each journal. The bearings are lubricated under pressure. Bridge dowels have been eliminated as the valve train uses floating valve bridges.Thermal efficiency is enhanced by the use of stainless steel thermal sleeves in each exhaust port. The sleeves reduce the amount of heat rejection to the cooling system. The sleeves then transfer the thermal energy to the turbocharger.The unit injector is mounted in a stainless steel adapter. This adapter has been pressed into the cylinder head injector bore.Pistons, Rings And Connecting Rods
The piston is a two-piece articulated design that consists of a forged steel crown and a cast aluminum skirt. Both parts are retained by the piston pin to the small end of the connecting rod. Oil from the piston cooling jets flows through a chamber which is located on one side of the crown. The oil returns to the sump through the hole on the opposite side of the crown. The pistons have three rings that are located in grooves in the steel crown. The top two rings seal the combustion gas. The bottom ring provides control of the oil. The top ring has a barrel face. This ring is a KEYSTONE ring with a plasma face coating. The second ring has a tapered face and the ring has a coating of chrome for the face. The third ring is the oil ring. This ring is double railed. This ring has a coating of chrome for the face. The third ring has a coil spring expander. There are four holes that are drilled from the piston oil ring groove to the interior of the piston. These holes drain excess oil from the oil ring.The connecting rod is a conventional design. The cap of the connecting rod is attached to the shank by two bolts that are threaded into the shank. Each side of the small end of the connecting rod is machined at an angle of 12 degrees in order to fit within the piston cavity. This allows maximum utilization of the available space for gas load.Crankshaft
The crankshaft converts the combustion force in the cylinder into rotating torque. The rotating torque powers the equipment. On this engine, a vibration damper is used at the front of the crankshaft in order to reduce the torsional vibrations. The torsional vibrations can cause damage to the engine.The crankshaft drives a group of gears (front gear train) on the front of the engine. The front gear train provides power for the following components: camshaft, water pump, oil pump, air compressor, fuel transfer pump and hydraulic pump.The crankcase has seven main bearings that support the crankshaft. The crankcase also has two bolts which hold the bearing cap to the block. The oil holes and the grooves in the shell for the upper bearing are located at main bearing journals 2, 3, 5, and 6. The holes and the grooves supply oil to the connecting rod bearings. The crankshaft has eight counterweights which are forged integrally. The eight counterweights are located at cheeks 1, 2, 5, 6, 7, 8, 11 and 12.To seal the crankcase, crankshaft seals are installed in the front timing gear housing and the flywheel housing.Camshaft
The camshaft has three lobes at each cylinder. These lobes allow the camshaft to operate the unit injector, exhaust valves, and the inlet valves. The camshaft is supported in the cylinder head by seven journals which are fit with aluminum bearings. A bearing is pressed into each journal. The camshaft gear contains integral roller dampers. The integral roller dampers counteract the torsional vibrations. The vibrations are generated as the fuel injector operation pressure is increased. The design reduces gear train noise. This design also increases the life of the gear train. The camshaft is driven by an adjustable idler gear which is turned by a fixed idler gear which is turned by a cluster idler gear in the front gear train. Each bearing journal is lubricated from the oil manifold in the cylinder head. A thrust plate that is located at the front positions the camshaft. Timing of the camshaft is accomplished by aligning marks on the crankshaft gear and idler gear, and camshaft gear with a mark on the front timing plate.