821684A 3 Mercury BOTTOM CARBURETOR

Illustration 1 g00748963The cylinder block has seven main bearings. The main bearing caps are fastened to the cylinder block with two bolts per each cap.Removal of the oil pan allows access to the following components:
Crankshaft
Main bearing caps
Piston cooling jets
Oil pump
Illustration 2 g00748989The cylinder head is separated from the cylinder block by a nonasbestos fiber gasket with a steel backing. Coolant flows out of the cylinder block through gasket openings and into the cylinder head. This gasket also seals the oil supply and drain passages between the cylinder block and the cylinder head. The air inlet ports are on the left side of the cylinder head, while the exhaust ports are located on the right side of the cylinder head. There are two inlet valves and two exhaust valves for each cylinder. Each set of inlet valves and each set of exhaust valves is actuated at the same time by the use of a valve bridge. The valve bridge is actuated by the pushrod. Replaceable valve guides are pressed into the cylinder head. The hydraulically actuated electronically controlled unit injector is located between the four valves. Fuel is injected directly into the cylinders at very high pressure. A pushrod valve system controls the valves. Piston, Rings And Connecting Rods
Illustration 3 g00773509
(1) Piston
(2) Piston cooling jet
(3) Connecting rod High output engines with high cylinder pressures require two-piece articulated pistons. The two-piece articulated piston consists of a forged steel crown that is connected to an aluminum skirt by the piston pin. Refer to the Parts Manual in order to obtain information about the type of pistons that are used in a specific engine.
Illustration 4 g00773499
(4) Compression ring
(5) Intermediate ring
(6) Oil ring
(7) Forged steel crown
(8) Aluminum skirt All of the rings are located above the piston pin bore. The compression ring is a Keystone ring. Keystone rings have a tapered shape. The action of the ring in the piston groove that is tapered helps prevent seizure of the rings. Seizure of the rings is caused by deposits of carbon. The intermediate ring is rectangular with a sharp lower edge. The oil ring is a standard type of ring or a conventional type of ring. Oil returns to the crankcase through holes in the oil ring groove.Oil from the piston cooling jets sprays the underside of the pistons. The spray lubricates the pistons and the spray cools the pistons. The spray also improves the piston's life and the spray also improves the ring's life.The connecting rod has a taper on the pin bore end. Two bolts hold the connecting rod cap to the connecting rod. The connecting rod can be removed through the cylinder.Crankshaft
Illustration 5 g00770993
(1) Crankshaft
(2) Gear The crankshaft converts the linear motion of the pistons into rotational motion. A vibration damper is used at the front of the crankshaft to reduce torsional vibrations (twist on the crankshaft) that can cause damage to the engine.The crankshaft drives a group of gears on the front of the engine. The gear group drives the following devices:
Oil pump
Camshaft
Hydraulic oil pump
Air compressor
Power steering pumpIn addition, belt pulleys on the front of the crankshaft drive the following components:
Radiator fan
Water pump
Alternator
Refrigerant compressorHydrodynamic seals are used at both ends of the crankshaft to control oil leakage. The hydrodynamic grooves in the seal lip move lubrication oil back into the crankcase as the crankshaft turns. The front seal is located in the front housing. The rear seal is installed in the flywheel housing.
Illustration 6 g00816002
Schematic Of Oil Passages In Crankshaft
(1) Oil gallery
(2) Main bearings
(3) Rod bearings 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 crankshaft is held in place by seven main bearings. A thrust bearing next to the rear main bearing controls the end play of the crankshaft.Vibration Damper
The force from combustion in the cylinders will cause the crankshaft to twist. This is called torsional vibration. If the vibration is too great, the crankshaft will be damaged. The vibration damper limits the torsional vibrations to an acceptable amount in order to prevent damage to the crankshaft.Rubber Vibration Damper (If Equipped)
Illustration 7 g00818663
Rubber Vibration Damper
(1) Crankshaft
(2) Ring
(3) Rubber ring
(4) Hub
(5) Alignment marks The rubber vibration damper is installed on the front of crankshaft (1). The hub (4) and ring (2) are isolated by a rubber ring (3). The rubber vibration damper has alignment marks (5) on the hub and the ring. These marks give an indication of the condition of the rubber vibration damper.Viscous Vibration Damper (If Equipped)
Illustration 8 g00816013
Cross Section Of Viscous Vibration Damper
(1) Crankshaft
(2) Weight
(3) Case The viscous vibration damper is installed on the front of crankshaft