Basic car mechanics

Friday 17th July 2015

I've just finished the second part of a two-part car mechanics course at Truro College, and it's been one of the best courses I've ever attended. Before I started the first part (they also run a ladies-only class) I barely knew how to change a wheel, but at the end of the second course we just stripped down an engine and re-assembled it.

It's given me huge amounts of confidence to fix cars myself, and I can now have conversations with garage mechanics without feeling like an idiot.

The main thing I've learned about cars is how incredibly basic and old-fashioned they are. Engines have barely changed since Karl Benz invented the Benz Patent-Motorwagen in 1886, and even then it's the same basic principle as Thomas Newcomen's atmospheric engine from 1712. Hot gas makes a piston move out, which is used to power something.

Cars have got faster, more efficient and cleaner, but the underlying concept has hardly changed. Even electric cars aren't a new idea: Thomas Parker, who electrified the London Underground, built the first working electric car, with rechargeable batteries, in 1884. According to Wikipedia, in 1900 "40 percent of American automobiles were powered by steam, 38 percent by electricity, and 22 percent by gasoline."

So here's a slideshow of my final lesson, showing our engine strip down. If it goes too fast for you to read, roll your mouse over the image and it will pause the slideshow.




This is one of the student engines from the course, it's a 1.3L overhead valve petrol engine from a Ford Fiesta. The first thing we're going to do is remove the cover at the top that says Endura-E on it.
Now that cover's gone, you can see the top of the valves. This is a four cylinder engine that has two valves per cylinder, one to let in the fuel/air mixture and one to let out the exhaust gases. Each of the valves is opened by a rocker that sits above it. The one on the far left is missing, probably eaten by a student. Now we're going to remove all the rockers.
With the rocker shaft removed, you can see the valve springs more clearly, and behind them you can see where the pushrods come up through the engine block. Now we're going to remove the cylinder head and see inside the engine.
This is the top of the engine block, with the head gasket at the top of the picture. The gasket is a just piece of soft metal that sits between the engine block and the cylinder head to keep the gases, water and oil separated. In the block you can see the four pistons, the inner two are at the bottom of their range of travel and the outer two are at the top..
This is the other side of the cylinder head, which fits onto the engine block. You can see the pairs of valves - the smaller, light coloured ones are the exhaust valves. Just above the valves you can see the spark plugs, which ignite the fuel/air mixture. On the left side is the missing valve.
This is a close up of one of the valve pairs, they're pretty dirty and so don't close perfectly. This lets gas leak out and will affect how much power the engine can produce. On the right side you can see the tip of the spark plug again.
This is a valve that's been removed. You can see the spring on the right side which forces the valve closed, and on the left side is the head which sits inside the cylinder. It's shiny round the edge because it has to make a very tight seal.
Here's the top of the cylinder with that valve removed. The seat, where the valve sits, should be perfectly clean and shiny too, but this one's really dirty. Enough about valves, let's look at something else.
This is the clutch, on the side of the engine. It attaches the engine to the transmission (gearbox). When you put your foot on the clutch pedal, the spines pointing into the centre get compressed and separate the engine from the transmission, which stops the engine powering the wheels. Let's take the clutch off.
Behind the clutch, attached to the engine block, is the flywheel. This is a really heavy bit of metal that helps to keep the engine spinning smoothly, as it evens out the changes in speed as the cylinders fire.
On the other end of the engine to the clutch and flywheel is the timing chain. Most cars have a rubber timing belt, also called a cam belt, but this particular engine uses a chain instead. Chains last longer, but they're much more noisy than a belt. At the bottom of the photo is the crankshaft, which is the power output from the engine, which drives the camshaft on the left side.
The engine is now upside down. This is a particularly bad photo of the oil sump, a large box that covers the bottom of the engine into which the oil drains. The engine pumps oil all around itself to keep it lubricated and cool, and eventually the oil all collects at the bottom, in the sump.
We've removed the sump, and this is a view looking at the bottom of the engine. You can see the sump strainer, which looks like a tea strainer, and keeps any shards of metal or other objects from getting back into the oil. There are five bearing caps, which are held in place by the large bolts, which keep the crankshaft in place. Let's remove the bearing caps.
With the bearing caps removed, you can see the whole of the crankshaft running across the middle of the engine. We've also removed the caps from the connecting rods, which attach to the pistons, and we've removed the piston from the far right - you can see the floor through the hole.
This is the piston we removed. On the left side is the connecting rod, which attaches to the crankshaft. When the piston is forced down by the expanding gas, it pushes on the connecting rod which pushes the crankshaft down and round. On the right side is the piston itself. There are three metal rings on the side of the piston which stop the gases inside the engine blowing out past the piston.
Now we've removed the crankshaft completely, sadly the picture I took of the crankshaft was completely blurry so I can't show you what it looks like. You can clearly see through the cylinder to the floor on the right hand side, and you can see the bottom of the other three pistons in their cylinders. Let's take the other pistons out too.
Now you can see through all four cylinders. The only part left to remove is the camshaft, which I also don't have a decent picture of. The camshaft is at the bottom of the picture, and has metal lobes that open and close the valves at the top of the engine.
With the camshaft removed, you can see the tappets, the shiny pins that the camshaft pushes to open and close the valves.
Finally, this is the top of the engine block with the pistons removed. It's still pretty heavy, even after we've removed all the parts, because it's a big solid lump of metal.

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