44467 1 Mercury GUIDE

Cylinder Head Assembly
The cylinder heads are a one-piece cast iron head. Two inlet valves and two exhaust valves, which are controlled by a pushrod valve system, are used for each cylinder. Valve guides without shoulders are pressed into the cylinder heads. The opening for the direct injection adapter is located between the four valves. Series ports are used for both inlet and exhaust valves.The valve lifters can be removed without the removal of the head. The removal can be made because of the size of the pushrod openings through the head.Pistons, Rings And Connecting Rods
The type of pistons that are in the 3408 or 3412 engine depends on the engine's application. These engines will have pistons that are made from aluminum or pistons that are made from steel. The crown of the piston 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 ring is a Keystone ring, which is tapered. The intermediate ring will be a Keystone ring for the aluminum piston, or a standard ring that is not tapered for the steel piston.The piston is designed for a direct injection engine. The piston has a cardioid design on the top surface. This piston design helps to improve combustion efficiency. The piston pin is held in place by two snap rings. These snap rings fit in grooves in the pin bore of the piston.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.Crankshaft
The crankshaft changes the combustion forces in the cylinder into usable rotating torque which powers the equipment. 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 (front gear train) on the front of the engine. The front gear train provides power for the following components: timing gears and oil pump. 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 bearing surfaces 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 crankshaft of the 3408 engine is held in place by five main bearings. The crankshaft of the 3412 engine 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
The engine has a single camshaft that is driven at the front end. The camshaft is supported by five bearings for the 3408. The camshaft is supported by seven bearings for the 3412. As the camshaft turns, the camshaft lobes move a lifter assembly. The camshaft lobe moves either two inlet valves or two exhaust valves for each cylinder. The camshaft must be in time with the crankshaft. The relation of the camshaft lobes to the crankshaft position causes the valves and injectors in each cylinder to operate at the correct time.Vibration Damper
The twisting of the camshaft is called torsional vibration. The torsional vibration is caused by the regular power impacts along the length of the crankshaft. The vibration damper is installed on the front end of the crankshaft. This vibration damper is used to reduce the torsional vibrations. This eliminates any damage that could occur to the crankshaft.There are two types of vibration dampers that are used on the 3408 and 3412 engine. The type of damper that is used will depend on the engine's application.The rubber damper is made of an outer hub connected to an inner hub by a rubber ring. The rubber makes a flexible coupling between the outer hub and the inner hub.The viscous damper consists of a casing that is welded to the inner hub. The casing contains a steel weight that is suspended in a viscous silicone lubricant. The silicone lubricant acts as a flexible coupling between the weight and the inner hub.