Operating instructions

DESCRIPTION
Engine
The engine is a four-cylinder carburettor unit with overhead valves. The pistons
are made of light-alloy and the upper compression rings on each piston are
chromed. The main bearing and big-end bearing shells are replaceable. The
crankshaft is statically and dynamically balanced.
Engine type B 20 A
has an output of 90 h.p. (SAE) and is equipped with a Zenith-
Stromberg horizontal carburettor.
Engine type B 20 B
has an output of 118 h.p. (SAE) and is equipped with twin
SU horizontal carburettors. (On certain markets twin Zenith-Stromberg hori-
zontal carburettors.)
Fuel system
Fuel is fed from the tank to the carburettor by a fuel pump which is driven by a
cam on the engine camshaft. There is a filter in the fuel pump which traps water
and other impurities in the fuel.
Exhaust emission control
The engine is fitted with exhaust emission control, that is, a system as a result
of better mixing and distributing of fuel and air provides a more complete
combustion and thereby cleaner exhaust gases. On the B 20 A engine, the exhaust
emission control is obtained through the carburettor which is specially design-
ed for this purpose. On the B 20 B engine the exhaust emission control is pro-
vided partly through carburettors specially designed for this purpose and partly
by the engine having a special induction manifold with throttles and preheating
chamber. When driving at low speeds the throttles are closed so that the fuel-air
mixture is forced to pass the preheating chamber.
When higher output is required, the throttles open so that the fuel-air mixture
flows directly to the cylinders.
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DESCRIPTION
Air preheating
Certain variations of the 120 models are provided with thermostatically con-
trolled air preheating.
With this arrangement the induced air is maintained at a constant, favourable
temperature. Air preheating counteracts ice formation in the carburettor and
also contributes to a shorter warming up period after starting from cold.
Lubricating system
The engine lubrication is taken care of by a gear pump which sucks up oil from
the sump on the bottom of the engine and forces it through the oil filter out to
the lubricating points in the engine. A relief valve is built into the oil filter which
prevents the oil pressure from reaching excessively high values.
Cooling system
The engine is water-cooled and the cooling system is of the pressure type.
Water is circulated by means of a pump fitted on the fan shaft. A wax-type
thermostat with an opening temperature of about 82°C (180°F) prevents the
cooling water from passing through the radiator before the engine has reached its
normal working temperature. On certain markets a fan with a slip-type coupling
is fitted.
Electrical system
The electrical system is of the 12-volt type and is fitted with a voltage-regulated
alternator. The starter motor is operated from the instrument panel by the igni-
tion key, which also switches on the rest of the electrical system. The cables
to the headlights, parking lights and internal lighting, however, are not taken
over the ignition switch but can be switched on and off without the ignition
key being in position.
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