Inside Engine

Assembling a diesel engine

Sure you know there is an engine driving your car, giving rimpull to your wheels, powering your hydraulic pumps, etc…

This post will present pictures and explanations from the assembly of a diesel engine, very common on industrial machines, such as trucks, construction equipment, generating sets to name a very few.

In this post, you will not learn how to assemble an engine, but you will only be exposed to the primary components that allow the engine to spin thousands of revolutions per minute and how components fit the entire engine set.

The engine below is an old version of diesel engines, in which fuel injection occurs through a fuel pump coupled with the timing gears unlike modern diesel engines where fuel injection occurs electronically through unit injection pumps governed by engine control units.

The engine below follows the 4 stroke engine principles: intake, compression, power and exhaust. During intake, the combustion chamber is filled with clean air rich with O2. At compression, the chamber is closed and air is compressed with injected fuel to the point where power phase is reached, pushing the piston downwards. Exhaust is the last phase allowing the combustion chamber to reject the spent air during combustion.

Steps for Assembly

# 1- This is the cylinder block, the housing component of the engine.

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# 2- That is another shot of the cylinder block. In these half-circles shape, sits the crankshaft.

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# 3- The crankshaft, under the action of combustion, rotates and thus transmits power out of the engine, to transmissions, hydraulic pumps or generators for instance.

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# 4- When you hear about 4 or 6 cylinders engine, it means that there are 4 or 6 pistons respectively in the engine. The piston is attached through its connecting rod to the crankshaft. The top face of the piston will feel the explosions during combustion process, will be pushed down and as a result turn the crankshaft. Piston rings that can be seen on the upper part of the piston allow lubrication and primarily prevent combustion pressure from getting lost out of the combustion chamber. Pistons complete a vertical movement of up and down inside what is know as cylinder liner.

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# 5- The camshaft is a smaller design of the crankshaft, responsible for synchronising the valve mechanism; in other words, the appropriate intake of air, outtake of exhaust and closing of combustion chamber.

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# 6- Picture below shows the crankshaft being assembled on the cylinder block. It can also be seen that pistons are fitted on the crankshaft.

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# 7- Timing gears are the “brain” of the engine. If the gears are installed wrong, the engine will never start or, at least, will not work optimally. Timing gears allow the crankshaft to synchronise with both camshaft and fuel pump (in old diesel engine versions). In other words, depending on the position of the piston, air valves, exhaust valves and fuel injection should be governed accurately.

For instance, during intake phase, air valves are open to allow air inside chamber, exhaust valves are closed, and fuel injection does not occur.7 copy

# 8- Oil pump, part of the lubricating system can be seen. It is responsible for oil circulation inside the engine and thus lubrication of the engine component. Oil lubrication is of crucial importance in many industrial components such as engines.

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# 9- To avoid confusion, this picture shows the engine upside-down. The oil sump seen below cover the lubricating system and acts as an oil bath.

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# 10- Turning back the engine to its normal position, picture below shows the cylinder heads installed on top of the cylinder block. They cover the top face of the pistons previously installed. You can see the movement of the pistons under the cylinder head in the first video below.

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# 11- Having installed the cylinder head, valve mechanism is now fitted. It is composed of rocker arms, push rods and a shaft to dictate the movement of the camshaft over the air and exhaust valves. In the second video below, you can see how the valve mechanism work when the engine is on.

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# 12- The valve mechanism is now covered. The upper plug seen is the oil plug where engine oil is filled.

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# 13- Cooling system of the engine is installed. The water pump can be seen and a mechanical thermostat is fitted in the water pipes. Thermostat directs the water to the radiator to be cooled only when the water temperature exceeds the thermostat’s specification.

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# 14- The dynamo or alternator attached to the crankshaft’s pulley through a belt rotate to generate a voltage to charge the machine’s battery.

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# 15- The starter motor is fed with enough power from batteries to start the engine. A pinion is pushed out through magnetic coil towards the flywheel and rotate to ignite the engine.

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# 16- The fuel pump installed shows 6 outputs, each to supply one injector with fuel. The  oval shape below the fuel pump is the oil cooler that allows water to cool the engine oil.

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# 17- The turbocharger sits on the exhaust manifold, and is fed with exhaust air allowing the turbine to spin at very high speeds. The action of the turbine compresses the air inlet, increases the intake air charge density, thus boosting power to the engine.

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# 18- During turbocharging, the air compressed becomes heated. Below is the path that heated compressed air takes to reduce its temperature before going to the combustion chamber. This phase serves to  increase the efficiency of combustion.

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# 19- Picture below ends the assembly of the engine. Fuel filters can be seen fitted on the engine fuel lines. On the other side of the engine, oil filters are fitted. Engine is now ready for test-run. You can watch the last video below.

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Engine is action

The video below reveals the movements of the inline-six engine pistons underneath the cylinder head. As we said earlier, 4-stroke engine refers to four piston movements to complete a cycle. Focus on one piston, and notice the intake phase when the piston absorb air in its downward movement. Following movement is compression during which piston goes up, before going down in the power stroke. Last stoke is the exhaust during which the piston goes up again to reject spent air during combustion. It should be mentioned that the positions at which the pistons stops to change directions are called ‘Top Dead Center or TDC’ and ‘Bottom Dead Center or BDC’.

Having finished engine assembly, visit this link to visualise how the orchestration of the valve mechanism allows an appropriate intake of clean air and outtake of exhaust and thus an optimal combustion.

Finally, the link below presents a full running simulation of the engine in the workshop. You can see that external set of batteries ignite the engine through the starter motor and an external barrel of water allow a suitable circulation of water in and out of the engine. Diesel is fed from an external container.

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