| How
the hell do Type 2's work ? Stop that bus, I
wanna get on..
Movin on up -
the gearbox
It's an explosive mixture - the carb and ignition.
It does it's thing
like this...
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Still with me ? There's some more
engine stuff coming now, so if
your feeling a bit lost why not go and get a cup of tea and re-read
the last couple of pages.
Attached to the crankshaft are the connecting rods, as their name suggests
these connect the crankshaft to the pistons. The pistons are busy popping up
and down inside the cylinders and are sealed as they go by the piston rings.
Ok so the pistons are doing their thing inside the cylinders, over the top of
the cylinders sits the cylinder head. As well as doing a good job of stopping
the pistons shooting off on some interplanetary quest, they also hold the
valves and valve train. There are two valves to each cylinder and they are
closed by valve springs (boing !), of the two valves, one is an intake valve the other is
an exhaust valve. They let in the fuel mixture to the cylinder and then let out the gases
after the cylinder has fried all that lovely mixture. All this stuff is held onto the
engine block by big long bolts called studs.Your
Type 2 bus engine is a four cycle engine, which means each cylinder
needs four cycles to produce any oomph. Lets talk about where that
fuel goes that you lovingly pour into the petrol tank every week. The petrol
is sucked into the fuel pump and then pushed into the carburettor by a
diaphragm (cut the sniggering, but yeah it's very similar), the diaphragm is
pushed up and down by the rod (I said, cut the sniggers)from the camshaft.
All that sucking and pushing action (now your just downright putting me off)
is made by valves in the pump. One valve opens to suck and closes to
push and the other opens to push and closes to suck. Anyhow the petrol
ends up in the carburettor bowl. Have you ever looked in the cistern on
your toilet, if not go and look. How was it ?..... you should have seen a
large float if you lift it up it lets more water in, drop it and it closes the valve.
There's a similar thing inside your carburettor bowl and it does exactly the
same thing.
From the carb. bowl the petrol flows down into the the
accelerator pump
which pumps the petrol into the carb. throat in a spray, this is operated by your foot on
that big bus accelerator pedal. The petrol's also flowing out to the jets. There are three
little jets, idling, middle speed and high speed. The jets are simply speaking holes which
hold petrol ready for it to be sucked into your Type 2 engine. There is also a
butterfly valve at either end of the carb. The one at the top is the choke and it limits
how much air gets in and so makes the fuel mixture richer. The one at the bottom is
attached to the accelerator pedal, it opens up the throat to the engine to control your
speed. Remember that accelerator pump I mentioned earlier ? that increases the amount of
petrol being used if you press hard on your accelerator. So that's how the petrol you pay
for at the petrol station gets used up. (N.B. you may not have a carb on your bay
bus, don't panic ! cus you've got electronic fuel injection, unfortunately I've only owned
early bay campers which never had it
so I can't comment on this. If anyone would like to add a paragraph on this
please drop me a line)
So we've got all that petrol swilling about and a method to increase or
decrease it depending on circumstance, there's one element missing
and that's fire. Whatever happens we are going to need to ignite that
fuel mixture and this is how it's done. Think about this, when you turn
your key in the bus cab, some current goes to the ignition system and
some to the solenoid on the starter. The solenoid is not in fact something
off the starship Enterprise like a tri-corder, but is actually an electro-magnet.
The solenoid engages the starter gear with the flywheel and also connects
a contact which draws power to turn the starter motor and hopefully starts
the engine.
As I've said some power goes to the ignition system namely
the ignition
coil. This is the cylinder attached to your fan housing with three wires
sticking out of one end (you can get attractive chrome sheaths for the
ignition coil, these are for the benefit of your ego not the engine). From the
coil the power goes to the distributor. This is the primary circuit which puts
12 volts into the ignition coil. The coil increases this charge massively to
about 10,000 volts which is discharged to the distributor. So there's this
huge bolt of electricity building itself up and needing thick cables to hold it,
why bother ?... well you need a big bolt of electricity to jump a gap and that's
exactly what we are asking it to do. The spark that's created travels along the
HT leads (thick cables from the distributor to the engine block) to the spark
plugs.
The distributor times when the sparks fly, opening and closing points as it
whizzes round and is driven by a gear from the crankshaft. When the points
are closed the 12 volt current grounds. A little thing called the condenser,
which is a small cylinder on the outside of the distributor, is part of the electricity
path while the points are open. The condenser stops the 12 volt current from
jumping the gap and going to ground.
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