3. ENGINE BASED SYSTEMS
3.1 The internal combustion engine
The internal combustion engine is the main source of electrical
and mechanical power for most mobile equipment, and for a large
proportion of all construction plant. An understanding of how
engines work, and how to disable them, is therefore a key part
of good sabbing technique.
By and large engines are either run on diesel or petrol - other
fuels such as gas or methanol are available, but these tend to
be used rarely, and so you are unlikely to come across them in
3.2 Petrol engines
The engines shown on the following page are rather old (modern
car engines have rather moved on) but they more easily indicate
different functions in the auto engine. Today, many cars have
separate electrically powered fans. Also the distributor and coil
system, which controls the firing of the engine, is being slowly
replaced by computer controlled units.
At its simplest the engine works as follows:
- To start the engine, power from the battery turns over the
starter motor - this automatically engages with the flywheel.
When the engine starts, the motor disengages;
- Fuel from the fuel tank is pumped to the carburettor. Here
a nozzle produces a fine mist of petrol to allow it to mix thoroughly
with air drawn in through the air filter;
- Taking just one cylinder - as the cylinder moves down a valve
in the cylinder head opens and the air/fuel mixture is drawn in.
At the bottom of the stroke the valve closes;
- As the piston returns back up the cylinder the air/fuel mixture
is compressed. At the point of maximum compression when the piston
is at the top of its stroke the spark plug sparks and the air/fuel
mixture explodes. The pressure increase caused by the hot gases
forces the piston back down the cylinder;
- When the piston reaches the bottom of the cylinder, another
valve opens and the exhaust gases are forced out of the cylinder
when the piston travels back up the cylinder again - the cycle
is then repeated all over again;
- The four cylinders (or more - large earth movers can have
16-24 cylinders) and pistons are arrange so that they all fire
at regular intervals. The power produced is then transferred by
the camshaft to rotate the flywheel and drive the clutch/gearbox
and drive shaft;
- Electrical power is generated by the alternator, which is
turned by the rotation of the engine (it is directly coupled by
a drive belt to the crankshaft);
- The valves are controlled by a camshaft which activates the
valves at specific moments. The camshaft is kept in synchronisation
by 'timing chains' or teethed belts which are connected to the
- The engine is kept cool by water which is circulated around
channels within the engine/cylinder block. The water is forced
around the system by a pump connected directly to the crankshaft;
- The moving parts of the crankshaft/piston system are kept
cooled and lubricated by oil which is stored in the sump. The
oil is also pumped around the engine/cylinder block by a pump.
Typical auto-engine system (figure 3)
Internal view of the engine (fig. 4) and External view
of the engine (fig. 5)
3.3 Diesel engines
The main difference with diesel engine is that they have no sparking
system on diesel engines. Injectors force the fuel/air mixture
into the cylinder. The higher levels of compression used in cylinder
then force the mixture to explode - it is the use of higher compression
which makes the combustion process more efficient in diesel engines.
Apart from this there is little difference between the two engine
Another key difference is the use of fuel pumps on petrol engines,
and the suction of fuel by the injectors in diesels. This means
that if a diesel engine runs out of fuel, the fuel system must
be 'bled' to remove the air before it will properly function again
(this is not necessary on a petrol engine).
3.4 Gas engines
Gas engines are becoming increasingly popular as a more efficient
and less polluting alternative to the use of petrol and diesel.
They run on either butane/propane, or liquified petroleum gas
Gas engines are broadly similar to diesels in that they directly
inject fuel and air rather than mixing them in a carburettor -
but unlike diesel they still use spark ignition.
Gas engines are present the same general problems in terms of
sabbing, but the main thing to be aware of is that the fuel system
uses highly flammable gases under pressure - therefore it is not
a good idea to cut any fuel lines or damage the injection system
- unless you want to do this deliberately in order to torch the
machine. Any spark following a release of gas, especially if you
are still near the machine, could be fatal. Likewise, trying to
make holes in a gas or LPG tank can have fatal consequences too.
3.5 Basic sabotage of engine systems
When considering how best to damage an engine, most public libraries
provide you with ample help. The numerous range of DIY car maintenance
manuals, on everything from scooters to small vans, give you graphic
descriptions of what certain parts look like, and how to conduct
'maintenance' on them. I advice you to study this resource closely.
You might also find it useful to enrol on a car maintenance workshop/evening
class at your local technical college.
Coming back to our earlier principles, there are four basic features
of the engine to consider when deciding how best to disable it....
Fuel injection/ignition system
As noted earlier, cutting the fuel lines to a engine is quick
and easy, but can also be easily repaired. It is also a potential
source of pollution of the environment if the fuel contaminates
soil, or enters storm drains. It can also spill all over you.
There are a few simple ways to disable the fuel system of an engine...
- Cut the fuel line at the tank (but this is easily fixed);
- Fill the tank with an foreign material to block the system
- soil or sand are the most usual substances to hand. Basically
you keep loading the stuff into the tank until it's full. This
is actually quite problematic because the tank must be removed
- Put substances into the tank to affect the performance of
the fuel - basically sugar or syrup cause an overload of carbon
which clogs the motor, and high energy hydrocarbon based liquids
such as acetone or hydrazine make the fuel burn so hot it damages
the engine. Both these options can be expensive to fix;
- Smash the fuel pump (petrol engines, and diesels with pumps
only) - relatively simple to fix in a day or too, and cost a little
more than just cutting the fuel line.
This option is less messy in terms of fuel spilling everywhere,
but holds the risk of starting a fires, especially if the engine
On a petrol engine, remove the air filter (if there is one) to
gain access to the carburettor. Then, using a cold chisel, hammer
the carburettor. Carburettors are normally made of cast aluminium,
and so it won't stand up to this treatment. To be on the safe
side, it is better if you cut the fuel line first, and douse the
whole engine/carburettor with water the prevent any sparks igniting
On diesels, again take your hammer and chisel, and break off the
injector, then stove in the ends of the injectors where they enter
the cylinder block. Injectors are expensive to replace, but stoving
in the thread makes things even harder.
The other option for petrol systems is to rip out the distributor
cap and leads. Also, after removing the cap, hammer the rotor
arm and contacts to create the maximum possible damage.
On newer petrol engines, where ignition and fuel injection is
computer controlled, trace the wires from the spark plugs back
to the box or unit containing the timing system. Then use the
standard approach for electrical appliances - hammer a blunt screwdriver
through the unit once or twice. This is an expensive thing to
Finally, on petrol systems and diesel systems (although its harder
on diesels because the injectors have to be replaced with a torque
wrench to the right tension), take out the spark plug or injector,
and drop one or two ball bearings into one cylinder only - the
engine won't fire properly if you put it in more than one cylinder.
Replace the plug/injector, and make everything as if no one had
ever been there. Then, when the engine is switched on, in just
a few minutes the piston and cylinder head are ruined - this is
expensive to cure.
The power train - that is the crankshaft, clutch, gear and differential
system which transfers power from the pistons to the wheels -
is vulnerable only in two respects.
Firstly, the engine sump, the gearbox and the differential (if
the vehicle has one) are all vulnerable to abrasives in their
lubricating oil. Further details on how abrasives can be used
are given in Volume I. There is little problem getting abrasives
into the sump - the oil filler provides a direct route. Getting
abrasives into the gearbox is tricky because of getting access
to the filler nozzle. You also have the same problem with the
differential (the differential is the bevel on the back axle of
most heavy lorries/construction plant which transfers the motion
of the drive shaft through 90o to turn the wheels).
The clutch has exactly the opposite problem - it should be kept
dry. If you can release the clutch housing, and spray in a mixture
of grease and sand, it does immense damage to the clutch plates.
The electrical system:
The electrical system essentially consists of the battery, the
alternator, the starter motor, the injector heaters (diesel only),
the distributor cap and sparking coil (petrol only). Some petrol
engines, especially older stationary engines, do not have alternators
- instead they have magnetos (like the dynamos on bicycles) which
are directly connected to the crankshaft.
When considering the electrical system you have three prime targets...
- The battery;
- The alternator;
- The starter motor;
- Cables and fuses.
The battery can be easily removed - that is a straightforward
task of removing each terminal connector and then loosening the
The alternator and the starter motor present different problems
- mainly how to damage a well constructed and enclosed electrical
device. If possible try and find an opening in the alternator/starter
motor housing. What you are looking for are bundles of copper
wire wound on metal formers. The simplest way to damage the wires
is to use a sharp chisel or screwdriver to hammer and cut/split
individual wires. If this is difficult, just try and drill your
way through the casing into the coils.
Another other option is to open up a hole in the casing, perhaps
with a drill, insert some sort of small funnel, and then pour
acid in to fill up the casing - the battery is a good source of
concentrated sulphuric acid, but ferric chloride will do just
Finally, for good measure, always cut or rip out any electrical
cables. This can be easily fixed, at much less cost than replacing
the alternator and starter motor, but it's good for annoyance
value. Also, if there is not time to sort out the electrics properly,
ripping out the wiring is very quick. Also keep an eye out for
any fuse boxes - a quick swipe with a hammer or the round end
of a crowbar will smash the fuses and more importantly the fuse