Hyundai Atos engine teardown, Part 1

The engine comes from a 1999 Hyundai Atos.

Back in 2013 and with 120,000 kilometers on its back, the engine started making a light knocking sound. Soon after, the knocking became louder and louder and it was obvious that the engine had developed a bad crankshaft bearing. Repairing such an old engine would be expensive and the repair could be unreliable so we decided to swap the engine with a used one.

I had the old engine left at a corner in my garage (no, I didn’t do the swap myself) so I decided to dismantle it piece by piece and maybe I could pinpoint the exact failed part. All main parts of the engine are still in place. What’s missing is the accessories (AC pump, power steering pump, alternator), the pulleys, the throttle body and the exhaust manifold.  In this article I won’t tear down anything, I will simply demonstrate the engine and describe its main parts.

So stay tuned for some serious engine porn!


(Click on the photos for full size)


Engine front

This is the front of the engine, like watching it from the opened bonnet. The big protruding metallic part at the bottom is one of the engine mounts.

The black can right above the engine mount is the oil filter.

Further above, the four big holes are the cylinder exhaust ports. Normally this is where the exhaust manifold is bolted.

The four smaller holes between the big ones are where the spark plugs are screwed.

The long thin tube at the left is the oil dipstick holder.

Engine backside

This is the rear side of the engine, ie the side that faces the passenger compartment.

There’s nothing really interesting here. The big metallic thing with the tubes is the intake manifold, which provides cylinders with atmospheric air. Right below the manifold and at the left, that leftover piece of black hose was probably originally connected to the heater core.

At the bottom, the black part is the oil pan (oil sump) and the drain bolt.

The horizontal plastic black tube that stands between the main engine and the intake manifold is the fuel rail. This is a hollow tube filled with gasoline under pressure and via the injectors feeds the engine with fuel.


Engine left side


This is the left side.

The small cog (1) is attached to the crankshaft and via a belt (timing belt) it rotates the big cog (3) which is attached to the camshaft.

The weird hole (3) is where the coolant pump is normally attached. The brown color is due to rust.

The silver disk at (4) is the fuel pressure regulator and is attached to one end of the fuel rail.

The intake manifold is at (5), while (6) is the oil pan. The black plastic part at the top (7) is the air filter box (the top cover is missing).


water pump

This is the coolant pump.


left side with water pump

And this is how it is normally mounted on the engine. The crosspiece with the four holes is where the pulley that drives the pump is screwed.

On new car engines all accessories are driven by a single Poly-V belt (serpentine belt). But on older engines like this one, each accessory was driven by its own v-belt. The coolant pump usually shared the same v-belt with the alternator.

There’s indication of oil leaking from the cylinder head gasket and possibly from the crankshaft garter seal.



This is the right hand side.

The thin red line shows the point where the block and cylinder head are joined.

The small disk with the holes at (1) is basically the other end of the crankshaft. This is where the flywheel is normally bolted.

The brown ring around it is the garter seal, a special spring loaded seal that keeps oil from seeping out of the gap between the engine block and crankshaft. This seal is basically constantly rubbing against the rotating crankshaft. Eventually these wear out, start leaking and need to be replaced.  But after several hundreds of thousands kilometers, the crankshaft will eventually develop a small groove at the point of contact with the seal. Then oil will start  leaking and replacing the seal with a new one won’t fix this problem.

Replacing that seal requires quite some work. The gearbox, clutch plate, clutch disk and flywheel have all to be removed first to gain access to the seal, so usually this procedure is combined with a clutch kit replacement.

flywheel back

This is the flywheel as seen from the inner side, ie. the side that makes contact with the end of the crankshaft. The teeth on its perimeter are engaged by the starter motor when starting the car.


flywheel front

This is the outer side of the flywheel. There are some threaded holes and protruding pegs on the perimeter for centering and  mounting the pressure plate.

flywheel with clutch

The friction disk, resting on the flywheel.

Its center is splined and mates with the end of the gearbox input shaft. The dark rim is the friction material, similar in composition with brake pad material.

The splined center piece is not rigidly connected to the rim, but via the four springs visible near the center.

Notice how the center part of the friction disk is thicker on one side. The thicker side goes towards the pressure plate, away from the flywheel.


On this particular car it will be immediately apparent if the disk was mounted backwards, because then it will be impossible to bolt the pressure plate into place.

On other cars it can be mounted both ways, but if mounted backwards there will be poor contact between the friction surfaces and the whole clutch assembly will overheat and fail soon. This is unfortunately a rather common mistake that even professionals sometimes do.

flywheel with disk and plate

And here is the pressure plate on top of the friction disk and flywheel.

Here I have casually placed the parts together and it can be seen that the friction disk spline is slightly off-center. If now the pressure plate was screwed in place on the flywheel, the friction plate would be sandwitched between the flywheel and the pressure plate and unable to move. Since the spline now is off-center, it will be impossible to slide the gearbox shaft in.

So it is imperative that the disk is well centered before the pressure plate is screwed in place.

When the clutch pedal is not depressed, the pressure plate presses the disk against the flywheel and all three rotate at the same RPM (engine’s RPM).

When the pedal is depressed, the clutch bearing (not shown above) is pushing against the center of the pressure plate diaphragm (the comb like part where some discoloration is visible) and this causes the pressure plate to separate a little from the flywheel, thus releasing the grip on the friction disk.  Therefore, the flywheel and pressure plate keep on rotating at the same RPM as the engine, but the friction disk (and in effect the gearbox) is disengaged.

But back to the engine now: The black hole at (2) is the other end of the camshaft and normally the distributor is attached there. The camshaft rotates the rotor inside the distributor and this determines the spark plug firing order.

Numbers (3) and (4) are the so called core plugs or freeze plugs. Most car engines are made with the sand casting technique. That is, the molten metal is poured into a mold made of some special sand. When the casting process is over, the sand has to be removed and for that reason some holes are left open. These holes are then plugged with those press-fit metal caps, else the coolant would leak out. There are several similar plugs in other parts of the engine.

In theory, in case the coolant freezes inside the engine, these plugs will pop out, relieve the pressure and the engine block won’t crack. This is why they are sometimes (erroneously) called freeze plugs. In practice, these plugs aren’t designed for that. Although they might pop out after the coolant freezes, that was probably accidental and one should not depend on that for engine protection.

Number (6) is the other end of the fuel rail. The two fittings are where the fuel input and return hoses are connected.

Number (5) is the point where the thermostat is installed.

thermostat housing

This is the thermostat housing, (I couldn’t find the thermostat itself) that is bolted at the side of the engine at (5). The white connector at the left is probably the temperature sensor connector. The thermostat is a valve that is normally closed and obstructs coolant flow towards the radiator. It opens up only when the coolant temperature rises above a set point, usually in the range between 80 to 90 degrees C.

If there was no thermostat in place, the coolant would continually flow through the radiator. Depending on the ambient temperature, that could mean that the coolant would stay at a very low temperature. Contrary to common belief, we don’t want the engine to run too cool, ideally it should be at around 80C. Any lower than that and there’s too much tear and wear in the engine and fuel efficiency drops down.

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9 Responses

  1. Γιάννης says:

    Συγνωμη, και μηχανικος δηλαδη ; Πολυμηχανος Οδυσσέας !

  2. denmazz says:

    Nice article…good porn…ahah…where is part 2 ?

  3. Wendy says:

    this is an awesome share. thank you!

  4. ALI says:


  5. SAMUEL F. CABAYLO says:

    Helpful and thankful for this info.

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