1673 DIESEL TRUCK ENGINE Caterpillar

Systems Operation


General Information

The 1673C Engine is a 638 cu. in. (10,5 liters) displacement, 4-stroke cycle, six cylinder, turbocharged, diesel engine. The cylinder bore is 4.75 in. (120,6 mm) and the piston stroke is 6.00 in. (152,4 mm). The firing order is 1-5-3-6-2-4. The engine weighs approximately 1940 lbs. (880 kg) without coolant or oil.

Inlet air filtered by a dry-type air cleaner, is compressed by a turbocharger before entering the engine cylinders. The turbocharger is driven by the engine exhaust.

A plunger and barrel-type fuel injection pump meters and pumps filtered fuel to a precombustion chamber for each cylinder. The fuel is delivered to the precombustion chamber under high pressure. Injection for each cylinder begins at 13 degrees and 30 minutes before the piston reaches top center on the compression stroke.

A hydraulic governor controls the fuel injection pump out-put to maintain a constant engine RPM under varying work loads. A speed limiting device, in the governor, limits engine speed until engine oil pressure builds up.

The engine is of overhead valve design, having one inlet and one exhaust valve for each cylinder. The camshaft, geared and timed to the crankshaft, actuates rocker arms and valves through mechanical lifters and push rods.

The timing gears are located on the front of the engine.

The starting system is direct electric and uses a 24-volt starting motor. A 12-volt starting motor is optional.

Coolant for the engine is used to cool the engine lubricating oil. A full-flow temperature regulator, in the cylinder head at the front of the engine, provides for quick engine warm-up, and allows free circulation of coolant after operating temperature has been reached.

Lubrication for the engine is supplied by a gear-type pump. The pump provides full pressure lubrication to the engine internal and external parts.

The lubricating oil is both cooled and filtered. Bypass valves in the oil cooler assembly provide unrestricted flow of lubricating oil to the engine parts when oil viscosity is high or, if either the oil cooler or the oil filter element should become clogged.

Air Induction And Exhaust

Air induction and exhaust system parts include: 1-Exhaust manifold. 2-Inlet manifold. 3-Engine cylinder. 4-Air inlet. 5-Turbocharger compressor impeller. 6-Turbocharger turbine wheel. 7-Exhaust outlet.

This engine has an exhaust driven turbocharger to provide compacted air to the cylinders.

The exhaust gases enter the turbine housing and are directed through the blades of a turbine wheel, causing the turbine wheel and a compressor wheel to rotate.

Filtered inlet air from the air cleaners is drawn through the air inlet of the compressor housing by the rotating compressor wheel. The air is forced to the inlet manifold of the engine and is compressed by action of the compressor wheel.

When the engine load increases, more fuel is injected into the engine cylinders. The volume of exhaust gas increases, this causes the turbocharger turbine wheel and compressor impeller to rotate faster. The increased RPM of the impeller increases the quantity of inlet air. As the turbocharger provides additional inlet air, more fuel can be burned; hence more horsepower derived from the engine.

The turbocharger is mounted to the engine exhaust manifold. All the exhaust gases from the diesel engine pass through the turbocharger.

The turbocharger bearings are pressure-lubricated by engine oil. The oil enters the top of the center section and is directed through passages to lubricate the thrust bearing, sleeves and the journal bearings of the turbocharger. Oil leaves the turbocharger through a port in the bottom of the center section and is returned to the engine sump.

1-Compressor wheel. 2-Thrust bearing. 3-Lubricating oil inlet port. 4-Turbine wheel and shaft. 5-Compressor housing. 6-Oil drain port. 7-Bearings. 8-Turbine housing (exhaust).

Maximum turbocharger speed is determined by the rack setting, the high idle speed setting and the altitude at which the engine is operated. The high idle speed and the rack setting are not the same for all altitudes.

------ WARNING! ------

If the high idle speed or the rack setting is greater than specified for the altitude at which the engine is operated, serious damage to engine or turbocharger parts can result.


The fuel pump rack has been set by qualified personnel for a particular engine application. The governor housing and turbocharger are sealed to prevent unqualified personnel from tampering with the adjustments.

The engine can be operated at a lower altitude than specified without danger of engine damage. In this situation the engine will perform at slightly less than maximum efficiency. When operated at a higher altitude, the rack setting and high idle speed setting must be changed.

Cylinder Head

This is an overhead valve (OHV) four stroke cycle engine; i.e., four separate piston strokes are required to complete the firing of one cylinder.

There are two in-head valves (inlet and exhaust) for each cylinder. The valves are actuated by the camshaft through mechanical lifters, push rods and rocker arm assemblies. The camshaft is timed to the crankshaft and turns at one-half crankshaft RPM. Rotocoil assemblies cause the valves to rotate during engine operation.

Correctly adjusted valves operate for many hours before they need to be reconditioned. Eventually, however, the valve faces and seats become pitted, causing loss of compression. The cylinder head contains valve seat inserts which can be replaced when the seats have been reground to the extreme limits.

Cored passages in the cylinder head direct coolant around the precombustion chambers and the area around the valve seats. The exhaust manifold is bolted to the cylinder head. The inlet manifold is formed by passages cast in the cylinder head.

1-Precombustion chamber. 2-Valve spring. 3-Lock (Keeper). 4-Rotocoil assembly. 5-Rocker arm assembly. 6-Push rod. 7-Air inlet passage. 8-Valve seat insert. 9-Valve.

Fuel System

The fuel system is a pressure type with a separate injection pump and injection valve for each cylinder. Fuel is injected into a precombustion chamber, not directly into the cylinder.

This is a schematic of the fuel system. Its parts are identified: 1-Supply tank. 2-Fuel injection valve. 3-Fuel injection pump. 4-Pressure gauge. 5-Final fuel filter. 6-Vent valve. 7-Pump housing manifold. 8-Bypass valve. 9-Transfer pump. 10-Primary fuel filter.

A transfer pump supplies fuel to the manifold from which the injection pumps get fuel. Before the fuel is delivered to the mainfold, it is filtered first by a primary filter which removes dirt particles, and later by a final filter which removes more minute particles.

The transfer pump can supply more fuel than is required for injection, so a bypass valve is built into the pump. The valve limits the maximum pressure within the supply system.

The injection pumps receive fuel from the manifold and force it under high pressure to the injection valves. The injection valves spray atomized fuel into the precombustion chambers.

An air vent valve in the system permits removal of air. Air is removed by opening the valve and pressurizing the fuel system. The system can be pressurized by using the priming pump. The vent valve must be open until a stream of fuel, without air bubbles, flows from the vent line.

Fuel Injection Pump Operation

The injection pump plungers and the lifters are lifted by lobes on the camshaft and always make a full stroke. The lifters are held against the cam lobes by springs.

The amount of fuel pumped each stroke is varied by turning the plunger in the barrel. Action of the governor moves the fuel rack which turns the pump gear segment on the bottom of the pump plunger.

Cross section of a fuel injection pump. Parts are: 1-Fuel manifold. 2-Inlet port. 3-Check valve. 4-Gear segment. 5-Pump plunger. 6-Spring. 7-Fuel rack. 8-Lifter. 9-Camshaft.

Governor Operation

The hydraulic governor maintains speed at the RPM selected.

When the engine is operating, the balance between the centrifugal force of revolving weights and the force of a compressed spring controls the movement of a valve. The valve directs pressure oil to either side of a rack-positioning piston. Depending on the position of the valve, the rack is moved to increase or decrease the fuel to the engine to compensate for load variation.

Pressurized lubrication oil, directed through passages in the fuel injection pump housing, enters a passage in the governor cylinder. The oil encircles a sleeve within the cylinder. The oil is then directed through a passage in the piston where it contacts the valve.

When the engine load increases, the revolving weights slow down. The weights move toward each other and allow the governor spring to move the valve forward. As the valve moves, a small passage in the piston opens to pressure oil. The oil flows through this passage and fills the chamber behind the piston. The pressure forces the piston and rack forward, increasing the amount of fuel to the engine. Engine RPM increases until the revolving weights rotate fast enough to balance the force of the governor spring.

This is a cross section of a hydraulic governor which identifies: 1-Collar. 2-Speed limiter plunger. 3-Lever. 4-Seat. 5-Governor spring. 6-Thrust bearing. 7-Oil passage. 8-Drive gear (weight assembly). 9-Cylinder. 10-Bolt. 11-Spring seat. 12-Weight. 13-Valve. 14-Piston. 15-Sleeve. 16-Oil passage. 17-Fuel rack. The governor valve is shown in the position when the force of the weights and the force of the spring are balanced.

When the engine load decreases, the revolving weights speed-up and the toes on the weights move the valve rearward, allowing the oil behind the piston to flow through the drain passage in the center of the valve. At the same time, the pressure oil between the sleeve and the piston forces the piston and rack rearward. This decreases the fuel to the engine and the engine slows down. When the force of the revolving weights balances the governor spring force, the RPM of the engine will be the same as before.

When the engine is started, the speed limiter plunger restricts the movement of the accelerator. When operating oil pressure is reached the plunger in the speed limiter retracts and the accelerator can be depressed to the HIGH IDLE position.

When the engine RPM is at LOW IDLE, a spring-loaded plunger within the lever assembly in the governor bears against the shoulder of the low idle adjusting screw. To stop the engine, the plunger must be forced past the shoulder on the adjusting screw.

Oil from the engine lubricating system lubricates the governor weight bearing. The various other parts are splash lubricated. The oil from the governor drains into the fuel injection pump housing.

Fuel Injection Valve

Fuel, under high pressure from the injection pumps, is transferred through the injection lines to the injection valves. As high pressure fuel enters the nozzle assembly, the check valve within the nozzle opens and permits the fuel to enter the precombustion chamber. The injection valve provides the proper spray pattern.

Fuel injection valve cross section. Parts identified are: 1-Fuel line assembly. 2-Seal. 3-Body. 4-Nut. 5-Seal. 6-Nozzle assembly. 7-Glow plug. 8-Precombustion chamber.

Lubrication System

This illustration identifies lubrication system components, oil passages and arrows to show the approximate direction of the oil flow in the engine. 1-Oil filter base (includes a bypass valve). 2-Oil passage through the rocker arm shaft. 3-Turbocharger oil reservoir in center section. 4-Oil cooler. 5-Oil cooler bypass valve. 6-Timing gears (in front compartment). 7-Oil pump (in front part of oil pan). 8-Oil filter case. 9-Oil pan (sump). 10-Oil manifold (in engine block assembly).

The components in the Lubrication System consists of a sump (oil pan), pump, oil cooler and oil filter. The engine contains an oil manifold and oil passages to direct the oil to the various parts.

The pump draws oil from the sump and forces the oil through the oil cooler, oil filter, into the oil manifold. The oil flows through connecting passages to the external and internal engine parts. A regulating valve in the pump body controls the maximum pressure of the oil from the pump.

When the engine is started, the lubricating oil in the oil pan is cold (cool). This cool viscous oil does not flow immediately through the oil cooler and oil filter. This cool oil forces bypass valves, in the oil cooler and oil filter base, to open and allows an unrestricted oil flow through the engine.

As the temperature of the oil increases the viscosity and pressure of the oil decreases and the oil filter bypass valve closes. Now, only filtered oil is delivered to all of the engine parts. Oil temperature continues to increase and the oil cooler bypass valve closes. The oil then flows through the oil cooler, through the oil filter and to the engine parts.

A contaminated, restricted oil filter element will not prevent lubricating oil from being delivered to the engine parts. The oil filter bypass valve will open allowing the oil to bypass the element.

The oil manifold directs lubricant to the main bearing supply passages, timing gear bearings, to a passage leading through the cylinder head to the valve rocker arm shaft and the rocker arms and valves.

Oil spray orifices, in the engine block near crankshaft main bearings, spray oil on the underside of the pistons. This cools the pistons and provides lubricant for the piston pins, cylinder walls and piston rings.

The connecting rod bearings receive oil through drilled passages in the crankshaft between the main bearing journal and connecting rod journal.

The oil draining from the valve rocker arms lubricates the valves, push rods and lifters. The camshaft cams and the intermediate and rear camshaft bearings are splash lubricated.

All timing gear bearings, except the accessory drive gear bearing, are pressure lubricated. Oil is supplied to the bearings through passages in the cylinder block. Accessory drive gear bearing is lubricated by oil draining from the accessory drive shaft housing.

When the engine is warm and running at rated speed, the oil pressure gauge should register in the "operating range". A lower pressure reading is normal at idling speeds.

A small orifice in the gauge connection prevents rapid gauge fluctuation. Check this orifice for dirt, if the gauge becomes inoperative.

Cooling System

The engine has a pressurized cooling system with the coolant circulated by a centrifugal-type gear driven, water pump. A water temperature regulator restricts coolant flow through the radiator until the coolant reaches operating temperature.

The coolant is circulated to the engine cylinder block, around the liners, into the cylinder head and around the precombustion chambers. It also cools the engine lubricating oil.

The arrows show coolant flow through the engine. The components identified are: 1-Coolant outlet to the radiator. 2-Temperature regulator housing. 3-Lubricating oil cooler. 4-Cylinder head. 5-Air compressor. 6-Radiator bypass coolant tube. 7-Cylinder block. 8-Water pump. 9-Coolant inlet from the radiator.

Coolant flows from the pump through the engine oil cooler before entering the cylinder block. The coolant then flows around the cylinder liners and through the water directors into the cylinder head. All of the coolant in the cylinder head flows to the temperature regulator, located in a housing on the left front corner of the cylinder head.

The water cooled air compressor receives coolant through a tube connected to the elbow on top of the water pump. The coolant returns through a tube from the air compressor head to the diesel engine cylinder head.

Until the coolant reaches the temperature required to open the temperature regulator, the coolant bypasses the radiator and flows directly back to the water pump.

When the coolant reaches the temperature required to open the temperature regulator, the coolant is then directed through the radiator.

A pressure relief cap assembly is used to control the pressure in the cooling system, and prevents loss of coolant through the radiator overflow tube.

Pressurizing the cooling system serves two purposes. First, it permits safe operation at coolant temperatures higher than the normal boiling point, providing a margin of cooling for intermittent peak loads. Secondly, it prevents cavitation in the water pump, and reduces the possibility of air or steam pockets forming in the coolant passages. Proper operation of the pressure relief cap assembly is essential. A pressure relief cap allows pressure (and some water, if the cooling system is too full) to escape when the pressure in the cooling system exceeds the capacity of the pressure cap. Loss of pressure will cause steam to form when coolant temperature is above the normal boiling point.

Cooling System Components

Water Pump

The centrifugal-type water pump has two seals to prevent leakage of water and lubricant. A vent line, from the elbow on top of the pump to the cylinder head, bleeds air from the pump when filling a dry system.

An opening in the bottom of the pump housing allows any leakage at the water seal or the rear bearing oil seal to escape.


The fan is driven by two V-belts, from a pulley on the crankshaft. Belt tension is adjusted by moving the clamp assembly which includes the fan mounting and pulley.

Water Temperature Regulator

The temperature regulator restricts the flow of coolant through the radiator until the coolant reaches operating temperature; approximately 170° F. (80° C.)

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