Parts of a Diesel Engine – Labeled Diagram with Names

All 18 parts on the diagram

Show the list

One cylinder, cut through 12

Cylinder block The cylinder is bored through it. The crankshaft turns in the bottom of it.
Cylinder head It closes the top of the cylinder and holds the valves. In this engine it also holds the injector, the glow plug and the precombustion chamber.
Piston On the way up it squeezes the air. The air gets hot enough to light the fuel. The burning fuel then pushes it down.
Connecting rod Turns the piston's up-and-down push into a turning push on the crankshaft.
Crankshaft Seen end on here, with the round journal it turns on. An arm goes out to the connecting rod, with a heavy counterweight on the other side.
Camshaft Here it sits over the valve under the top cover. Many diesels have it down in the block instead, with push rods up to the valves.
Exhaust valve Each cylinder also has an intake valve, which lets the air in. This cut passes through the exhaust valve only.
Oil pan The oil pump draws from it. In British English it is the sump.
Fuel injector A diesel has one for each cylinder and no spark plugs. The fuel lights by itself in the hot squeezed air.
Glow plug A pencil-shaped rod with a tip that glows hot. It warms the chamber before the engine is cranked.
Precombustion chamber The fuel is sprayed in here and starts to burn. It then bursts through a narrow throat into the cylinder. Many diesels have none and spray straight into the cylinder.
Exhaust manifold It bolts to the side of the head. It leads to the turbocharger or the exhaust pipe.

The engine from the side 6

Injection pump This kind has one small pump for each cylinder in a row. It times each squirt and measures how much fuel goes in.
Injection lines One for each cylinder. They are also called high-pressure fuel lines.
Fuel filter Fuel from the tank comes through it to the injection pump.
Intake manifold A diesel draws in air only. The fuel is added later by the injectors.
Turbocharger The exhaust gas spins a turbine. The turbine drives a compressor that pushes air into the intake manifold.
Flywheel Its weight keeps the engine turning smoothly between power strokes. Here you see its toothed edge.

How this list was compiled: Part names checked on 2026-09-30; a name is kept only when two independent sources use it. The two curriculum texts are one publisher and count as one source. (1) US Army TM 9-8000, Principles of Automotive Vehicles, 1985, chapters 2, 3 and 5 and the glossary, https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 (cylinder block, cylinder head, piston, connecting rod, crankshaft, camshaft, intake and exhaust valves, oil pan, flywheel, intake and exhaust manifolds, injector, multiple unit injection pump, fuel supply pump and fuel filter, high pressure lines, precombustion chamber, glow plug, turbocharger). (2) Mid-America Vocational Curriculum Consortium, Diesel Mechanics: Fundamentals, 1982, https://archive.org/details/ERIC_ED220629, and its later edition Diesel Technology: Engines, 2002, https://archive.org/details/micro_IA41153662_0473 (cylinder block, cylinder head, piston, connecting rod, crankshaft, camshaft, exhaust valve, oil pan, flywheel, intake and exhaust manifolds, fuel injection nozzle, fuel injection pump, fuel injection lines, fuel filter, glow plugs, turbocharger). (3) Wikipedia, Diesel engine, Glow plug, Indirect injection and Injection pump, text only (injectors, injection pump, high-pressure fuel lines, glow plug as a pencil-shaped heater, precombustion chamber in the cylinder head, turbocharger, crankshaft, piston, cylinder head). Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's engine, nothing traced. Licence: own work

How it works

The parts of a diesel engine are mostly those of any piston engine: block, head, piston, connecting rod, crankshaft, camshaft and valves. What sets it apart is the fuel system: injectors and an injection pump, and no spark plugs.

Read the full guide

One cylinder, cut through

The camshaft opens the valve in the cylinder head. The piston rises in the block and squeezes the air until it is very hot. Then the fuel injector sprays fuel in, here by way of a precombustion chamber, and the fuel lights by itself. The push goes down the connecting rod to the crankshaft. The glow plug only helps a cold start.

From the side

Fuel goes from the fuel filter to the injection pump, then up an injection line to each injector. Air comes in through the turbocharger and the intake manifold. The flywheel is on the back of the crankshaft.

No spark plugs and no carburetor: that is the quick way to tell a diesel.
A glow plug is a heater, not a spark plug. It is on only for starting.

Questions and answers

What are the main parts of a diesel engine?

A cylinder block and head, pistons, connecting rods, a crankshaft, a camshaft and valves, as in any piston engine, plus a diesel's own fuel system: a fuel filter, an injection pump, injection lines and an injector for each cylinder.

How is a diesel engine different from a gasoline engine?

It has no spark plugs. It squeezes air alone, much harder than a gasoline engine squeezes its mixture, and the heat of that squeeze lights the fuel as the injector sprays it in.

What does a glow plug do?

It is a small electric heater with a tip that glows hot. It warms the chamber so a cold diesel will start, and it is not needed once the engine is warm.

What does the injection pump do?

It sends fuel to each injector at high pressure, at the right moment and in the right amount. The amount depends on how far the accelerator is pressed and how fast the engine is turning.