Page 100 - Car South Africa (February 2020)

tech
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SEATBELTS AND TURBOS
1. Disconnecting seatbelt
reminders
Many of us have partners who
don’t buckle their seatbelt
until we reach the end of the
street. Instead of listening to
the loud buzzer reminding
them to act more quickly, some
people choose to disconnect
the weight sensor to stop the
annoying sound. In the Renault
Duster, there are two connec-
tors per seat.The driver’s seat
is usually left untouched as
the steering wheel is too close
for the pre-tensioned seatbelt
to prevent contact in a crash.
The thinking is the passenger
side has more space and, thus,
the seatbelt is suf cient in case harm or even kill the person rather
the airbags don’t deploy as the
disconnected seat sensor may
disable the airbag deployment.
2. Boost pressure
I'm trying to work out a rough
guide for equivalent engine
sizes between a smaller, tur-
Splines to
transmission
shaft
TECH
101
Automotive
tech can be
puzzling. To
ease the
confusion,
each month
we explain
how a part of
your vehicle
works
98 CAR FEBRUARY 2020 CARmag.co.za
Let our team of technical experts
answer your motoring queries. If we
can’t, we know someone who can
bocharged engine and a larger, 2. Boost pressure of a turbo is gauge related part that could cause
naturally aspirated engine pressure, meaning above atmos- this issue, including the electri-
where all variables are xed pheric. The modern turbo controller cal system and carburettor, but
except the boost pressure which normally works to an absolute the problem persists. Any idea
increases incrementally. Howev- pressure threshold; for example, what they may have missed?
er, I need to clear up some con- two bar, so it would have to boost ELSIE DE JAGER
fusion. If atmospheric pressure more in Gauteng than at the coast Via email
at sea level is one bar, is a turbo to get to the boost setpoint. The only
pushing one bar of boost added limitation is turbo speed which may The idle condition is a tricky one
to the atmospheric pressure? be limited to, say, 200 000 r/min. as so little air and fuel is needed
BRIAN YOUNGBLOOD Therefore, it may not be able to to keep the engine running. Any
Fish Hoek achieve the absolute boost setpoint slight problem will affect idling. As
at high altitudes. Power is a function the engine is running ne, it points
1. It depends on the safety calibra- of air ow so, in general, two times to a small problem with the air
tion of the vehicle but, usually, an the air equals two times the power and fuel reaching the engine. We
airbag will not deploy if the seatbelt (as fuelling is adjusted accordingly). think your mechanic is on the right
is not worn. The reason is an airbag Obviously, this ignores limitations track but needs to consider doing
activates with such force that, if such as knock in a petrol engine, etc. the following:
the occupant’s body is not in the • Look for air leaks by following
desired, restrained position, it can the path from the air cleaner and
the carburettor through to the
than save their life. We maintain it’s MAZDA 323 IDLE PROBLEM engine intake. The slightest air
not worth the risk to disconnect the I need CAR’s help and wisdom leak will cause trouble, especially
seat’s mass-detection sensor for two regarding my 1990’s Mazda 323. between the carburettor and
reasons: the airbag may not deploy Last Friday, the vehicle cut out intake manifold.
during a crash; or the occupant fails when I stopped at a traf c light. • There should be an idle path
to buckle up as the “annoyance fac- It now won’t idle at all. My me- in the carburettor for air and
tor” of the seatbelt warning is gone. chanic checked every possible fuel; sometimes a separate idle
CLUTCH PLATE
Friction material
The clutch plate of a vehicle fitted with a manual
transmission sits between the flywheel of the engine
and the transmission. The flywheel, connected to the
engine’s crankshaft, transmits the engine torque through
the clutch plate to the transmission’s input shaft when
engaged. The clutch plate and pressure plate form a unit
that allows the engagement and disengagement of the
clutch. A bad driving habit is to “ride the clutch” when
stationary on a hill and not employ the handbrake. This
causes unnecessary wear of the friction material of the
clutch as it is continuously sliding across the mating
surface of the flywheel in this condition. The distinctive
clutch smell comes from the friction material as it
Springs function overheats and serves as a warning to the driver they are
as dampers to
lesson shudder and abusing the clutch and shortening its lifespan.
vibration