Free 3D model · STL · GLB · AR
By Parth Parmar, mechanical design engineer · 207 pieces, 62 parts · Updated
A marine diesel engine burns fuel in a four-stroke cycle: it draws in air, squeezes it until it is hot enough to ignite fuel sprayed into it, lets the burning gas push the pistons down, then pushes the exhaust out. In an inline-six a cylinder fires every 120°, and sea water carries the heat away through a heat exchanger.
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Live 3D: drag to turn it, pinch to zoom, explode it, cut it open, X‑ray it and watch it run. Free, in your browser, no app. Open it full screen →
Single parts: scroll to the parts list. These are learning models, not a print kit: some parts touch or overlap and there are no fit tolerances.
Free for personal and educational use under CC BY-NC 4.0. Credit “Engine-X by Parth Parmar (engx3d.com)” when you share or remix it. Don’t sell the files or prints. For commercial use, get in touch. Every file carries the Engine-X mark and a hidden digital fingerprint that identifies it.
| Machine | Inline-6 · NT855 Big Cam style · 14 L · PT fuel system |
|---|---|
| Parts modeled | 207 named parts in 8 systems (62 different parts to download) |
| Model size | 1560 × 1384 × 760 mm (real scale) |
| Formats | GLB (glTF 2.0) 9.6 MB, STL 7.1 MB, USDZ for iPhone AR, ZIP of part STLs 1.2 MB |
| Live 3D | Engine‑X atlas: true motion, explode, section, X‑ray |
| License | CC BY-NC 4.0, free with credit |
| Crank train | 8 parts: Crankshaft, pistons, connecting rods, flywheel and damper. |
|---|---|
| Camshaft & valve train | 16 parts: Camshaft, followers, push tubes, rocker levers, crossheads, 24 valves and their springs. |
| PT fuel system | 7 parts: PT pump, filter, supply and drain lines, and six cam-driven unit injectors. |
| Turbo, air & exhaust | 7 parts: Turbocharger, aftercooler, intake and water-cooled exhaust manifold. |
| Marine cooling | 9 parts: Heat exchanger, sea water pump, coolant pump and thermostat: fresh water inside, sea water outside. |
| Lubrication | 5 parts: Oil pan, oil, oil cooler, filters and dipstick. |
| Block & heads | 6 parts: Cylinder block, wet liners, three cylinder heads, rocker housings, main caps and gear cover. |
| Flywheel housing & mounts | 4 parts: Flywheel housing, starter, flexible mounts and the base plate. |
Every part with a picture, what it does and its own STL file: crankshaft, crankshaft gear (30 teeth), vibration damper, flywheel, flywheel ring gear, piston, piston pin, connecting rod and more. Open any part in the live 3D atlas to see where it sits and how it moves. A part used several times (valves, bolts) is shown once with its count.
↓ Download all parts · ZIP · 1.2 MB
Crankshaft, pistons, connecting rods, flywheel and damper.
The crankshaft. Six throws turn the pistons' up-and-down motion into rotation. Throws 1 and 6, 2 and 5, 3 and 4 share a direction, 120° apart, so a cylinder fires every 120° of rotation.
Counterweights opposite each throw balance the rotating mass. An inline six is naturally in balance, so it needs no balance shafts.
Seven main journals: one between every pair of cylinders and one at each end.
The crankshaft gear, which drives the camshaft gear and through it the whole valve and injection timing.
The vibration damper on the front of the crankshaft. A long six-throw crankshaft twists back and forth slightly with each power stroke; the damper absorbs that torsional vibration before it can crack the crank.
The flywheel. Its mass smooths the speed between power strokes, and its rear face drives the marine gearbox or generator.
The flywheel ring gear, which the starter motor engages to crank the engine.
A piston. Diesel fuel sprays into the bowl in its crown, where the air is hottest. The rings seal the combustion gas above and scrape the oil below.
Bore 140 mm: at 1800 rpm the mean piston speed is about 9.1 m/s.
The piston pin (wrist pin). It links the piston to the connecting rod and lets the rod swing as the crank turns.
A connecting rod, about 292 mm between centres. It carries the combustion force from the piston to the crankpin, in compression on the power stroke and in tension at the top of the exhaust stroke.
Camshaft, followers, push tubes, rocker levers, crossheads, 24 valves and their springs.
The camshaft. It turns at half crankshaft speed and has three lobes per cylinder: intake, injector and exhaust. "Big Cam" refers to its larger diameter; Big Cam engines from 1976 on moved from 2 in to 2.5 in cam journals so the injector lobe could build higher injection pressure.
The middle lobe of each set drives the unit injector, not a valve.
The camshaft gear. It has twice as many teeth as the crankshaft gear, so the camshaft turns once for every two crank turns, once per full four-stroke cycle.
A cam follower. It rides on its cam lobe and lifts the push tube whenever the lobe comes round.
A push tube. It carries the follower's lift up through the block to the rocker lever in the head.
A rocker lever. Its push-tube arm is shorter than its valve arm (59.666295470957664 : 90 mm), so 1 mm of cam lift becomes 1.5083892721948382 mm at the valves or injector.
A cam follower. It rides on its cam lobe and lifts the push tube whenever the lobe comes round.
A push tube. It carries the follower's lift up through the block to the rocker lever in the head.
A rocker lever. Its push-tube arm is shorter than its valve arm (59.666295470957664 : 90 mm), so 1 mm of cam lift becomes 1.5083892721948382 mm at the valves or injector.
A cam follower. It rides on its cam lobe and lifts the push tube whenever the lobe comes round.
A push tube. It carries the follower's lift up through the block to the rocker lever in the head.
A rocker lever. Its push-tube arm is shorter than its valve arm (59.666295470957664 : 90 mm), so 1 mm of cam lift becomes 1.5083892721948382 mm at the valves or injector.
A crosshead (valve bridge). One rocker pushes it, and it opens a pair of valves together.
An intake valve. During the intake stroke it lets compressed, cooled air from the turbo and aftercooler into the cylinder.
A valve spring. It closes the valve again and keeps the follower pressed on its cam lobe.
A crosshead (valve bridge). One rocker pushes it, and it opens a pair of valves together.
An exhaust valve. It opens near the end of the power stroke and lets the burnt gas out to the exhaust manifold and turbocharger.
Exhaust valves run much hotter than intake valves, so they are made of heat-resistant steel.
PT pump, filter, supply and drain lines, and six cam-driven unit injectors.
A PT unit injector, one per cylinder in the centre of the head. Fuel from the PT pump arrives at low pressure; the injector cam then drives the plunger down and forces the metered fuel through tiny holes into the cylinder at over 1,300 bar.
"PT" stands for pressure-time: the amount of fuel depends on the fuel pressure and the time the metering hole is open.
The injector plunger and link. The injector rocker pushes it down near the end of the compression stroke to inject; a spring lifts it back.
The PT fuel pump. A gear pump draws fuel from the tank; a governor and the throttle set the fuel pressure in the supply line, and that pressure decides how much fuel each injector meters.
On the PT system the pump only sets pressure. The injectors themselves build the high injection pressure.
The fuel filter. Clean fuel matters a great deal: unit injectors have very fine clearances.
Fuel line. Supply fuel runs to every injector, and the unused fuel returns to the tank, carrying heat away from the injectors.
Fuel line. Supply fuel runs to every injector, and the unused fuel returns to the tank, carrying heat away from the injectors.
Fuel line. Supply fuel runs to every injector, and the unused fuel returns to the tank, carrying heat away from the injectors.
Turbocharger, aftercooler, intake and water-cooled exhaust manifold.
The water-cooled exhaust manifold. On a marine engine it has a water jacket, so the hot surfaces in the engine room stay cool.
Classification rules limit hot surfaces in engine rooms, which is why marine manifolds and turbos are water-cooled or lagged.
The turbocharger. Exhaust gas spins the turbine, and on the same shaft the compressor pushes extra air into the engine, so more fuel can burn.
The turbo rotor: turbine wheel and compressor wheel on one shaft, spinning many times faster than the crankshaft.
The water-cooled exhaust elbow (riser) on the turbine outlet, leading to the boat's exhaust system.
The crossover pipe from the compressor outlet to the aftercooler.
The aftercooler and intake manifold. Compressing air heats it; the aftercooler cools it again so it is denser and the engine makes more power with lower temperatures. The "A" in NTA855 means aftercooled.
Heat exchanger, sea water pump, coolant pump and thermostat: fresh water inside, sea water outside.
The heat exchanger and expansion tank. Engine coolant (fresh water) flows around the tubes; sea water pumped through the tubes carries the heat overboard. Sea water never touches the engine's insides.
The heat exchanger tube bundle. Sea water flows inside these tubes. A zinc anode (not shown) protects them from corrosion.
The sea (raw) water pump. It draws sea water through the hull strainer and pushes it through the heat exchanger and aftercooler.
The flexible rubber impeller of the sea water pump. If the pump runs dry, this impeller burns up within seconds.
Changing this impeller is a routine marine maintenance job.
The fresh water (coolant) pump. It circulates coolant through the block, heads and heat exchanger in a closed circuit.
The thermostat housing. It holds coolant inside the engine until it is warm, then sends it to the heat exchanger.
Oil pan, oil, oil cooler, filters and dipstick.
The oil pan (sump). It holds the engine oil under the crankshaft.
The oil cooler. Engine coolant flows around it and keeps the oil temperature in check.
An oil filter. It catches wear particles and soot before the oil reaches the bearings.
An oil filter. It catches wear particles and soot before the oil reaches the bearings.
Cylinder block, wet liners, three cylinder heads, rocker housings, main caps and gear cover.
The cylinder block, one iron casting that carries all six cylinders, the crankshaft and the camshaft. It is 14.0 litres of displacement in a block about 1.1 m long.
Drawn see-through so the moving parts stay visible.
A wet cylinder liner. The piston runs inside this replaceable sleeve, and coolant flows directly around its outside. When a bore wears, a mechanic swaps the 140 mm liner instead of re-boring the block.
O-rings at the bottom seal the coolant from the crankcase. Leaking liner seals put coolant in the oil.
A cylinder head. Like the real engine, each head covers two cylinders, so a six has three heads. It carries four valves and one unit injector per cylinder, with coolant passages around them.
Three short heads are easier to lift and less prone to warping than one long head.
The rocker housing and cover over one head. It carries the rocker shaft for two cylinders and keeps oil in and dirt out.
A main bearing cap. It bolts to the block and clamps the crankshaft main bearing shells around a journal.
Flywheel housing, starter, flexible mounts and the base plate.
The flywheel housing. It closes the flywheel and is where the marine gearbox or generator bolts on.
The starter motor. Its pinion meshes with the ring gear to crank the engine.
A flexible engine mount. Rubber elements isolate the hull from engine vibration.
The base plate (engine bed) the engine mounts are bolted to, standing in for the boat's engine beds or a genset frame.
How does it work? Read the step-by-step guide, with key facts and common questions.
How a marine diesel engine works →Yes. The marine diesel engine 3D model is free for personal and educational use under CC BY-NC 4.0: credit "Engine-X by Parth Parmar (engx3d.com)". Selling the files or prints, or other commercial use, needs written permission.
GLB (glTF 2.0) with colours and named parts, STL in millimetres (Z-up) for CAD, slicers and 3D printing, USDZ for AR on iPhone, and a ZIP with all 62 parts as separate STL files.
207 named pieces in 8 systems (crank train, camshaft & valve train, pt fuel system, turbo, air & exhaust, marine cooling, lubrication, block & heads, flywheel housing & mounts). Repeated pieces such as bolts are folded together, which leaves 62 different parts, each one downloadable on its own.
Yes, download the STL (whole machine or single parts) and open it in your slicer. It is a learning model at real scale, not a print kit: some parts touch or overlap and there are no fit tolerances, so scale it and print parts one by one.
Tap "View in your room" on this page. Android opens Google Scene Viewer and iPhone opens AR Quick Look, both without an app, and you can place the model at real size on the floor or a table.
Yes. Tap "Play live 3D here" or open the Engine-X atlas (engx3d.com/atlas#m=diesel855): it runs in the browser with true motion, and you can explode it, cut it open and X-ray it.
Credit line: Marine diesel engine 3D model, Engine-X by Parth Parmar (engx3d.com)
Citation: Parmar, P. (2026). Marine diesel engine 3D model [3D model, CC BY-NC 4.0]. Engine-X. https://engx3d.com/3d-models/marine-diesel-engine
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