Arctic Cat Sno Pro 120 2011, Руководство по обслуживанию

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1-4
Other more complicated methods exist such as engage-
ment notches and changing the position of the cam arm
center of gravity in relation to the roller. This is called
“tucking the weight” and can be used, but, like the
engagement notch, it can hurt belt life.
The driven clutch will also play a part in CVT tuning for
high altitude operation. A steeper helix (torque bracket)
angle in the driven clutch will mean a quicker up-shift. A
shallower angle will mean a slower up-shift. If the up-shift
is too quick, due to a very steep helix, RPM will be pulled
down under the peak operating RPM of the engine (where
the horsepower is) and performance will suffer. The
engine may even bog. If you have a helix that is too shal-
low, the engine may over-rev or have poor acceleration.
Usually, angles shallower than the sea level calibrations
work best. The driven spring will also affect driven clutch
tuning. Tighten the spring, and RPM will increase. Loosen
the spring, and RPM will decrease. The spring should be
used to fine-tune and complement the helix selection.
Carburetor calibration changes for high altitude operation will
have an effect on the CVT system and how it operates. Under-
standing the basics of CVT operation is important in order to
make the correct high altitude CVT calibration changes.
ENGINE
A normally aspirated engine will generate more horsepower
at sea level than it does at higher altitudes. Many reasons for
this are possible, but the biggest reason is that the higher
you go, less oxygen is available for the engine to use during
its combustion process. Less oxygen means it needs less
fuel to obtain the correct air/fuel ratio to operate properly.
This is why the fuel ratio has to be recalibrated. High alti-
tude engines operate as though they have a lower compres-
sion ratio. This, along with less oxygen and less fuel, means
that the engine generates less horsepower.
The carbureted models will also have lower pressure
applied to the float chamber because of pressure changes
in the atmosphere between high altitude and sea level.
All of these characteristics will become more evident the
higher the altitude.
It will be necessary to make changes to the fuel systems
(carbureted models) and drive systems that support
engine operation as altitude changes.
TURBOCHARGING
Turbocharging is one method of compensating for loss of
air density that works extremely well when applied to
four-cycle internal combustion engines.
Exhaust gasses are directed through the turbocharger tur-
bine wheel which is attached to the compressor through a
common shaft. As the exhaust gasses spin the turbine, the
compressor is spun at very high RPM. Inlet air is drawn into
the compressor, compressed, and routed to the intake mani-
fold of the engine. Intake pressure, therefore, is maintained
at the optimum level as altitude or temperature increases.
The turbocharger output must be regulated to maintain the
optimum manifold pressure throughout the designed operat-
ing range. This is accomplished by regulating the volume of
exhaust gasses passing through the turbine by controlling a
diverter valve (waste-gate) at the turbocharger turbine inlet.
At lower altitudes/temperatures, excessive exhaust gasses
are diverted past the turbine and into the exhaust down-
stream of the turbocharger thus limiting the compressor out-
put to maintain correct manifold pressure.
As altitude increases, the manifold pressure is held con-
stant by diverting less exhaust past the turbine, thus
increasing compressor speed. This will continue until the
waste-gate is completely closed at which time manifold
pressure will start to decrease much the same as a nor-
mally aspirated engine.
The waste-gate is controlled by a spring/diaphragm
mechanism that is connected to the intake manifold by an
air line. A mechanical linkage connects the diaphragm to
the waste-gate control arm.
Air is heated by friction and compression through the tur-
bocharger and air density is lost by heating the air; there-
fore, an after-cooler is installed between the turbocharger
compressor and the intake manifold. This is an air-to-air
after-cooler that uses outside air directed through a radia-
tor-type cooler to cool the compressed air prior to enter-
ing the intake manifold.
SUSPENSION
The different riding styles of the individual operator, the
varying snow conditions, and the type of terrain are all
factors that affect the suspension at high altitude. Trail
riding versus powder snow riding versus combination
riding will all require different suspension settings.
The normal setting for front ski suspension is as little
spring pre-load tension as possible for powder snow rid-
ing allowing the skis to float across the snow with the
least amount of resistance. Trail riding will require more
spring tension to carry the varying load more effectively.
Many different settings and spring tensions to consider
exist when adjusting for riding style and snow condi-
tions.
The rear suspension has a number of spring settings that
produce different riding characteristics.
The front arm spring and shock will also affect the ride
and handling when either on a trail or in powder snow. A
strong spring setting on this shock will cause the snow-
mobile to tend to “dig” more when riding in the powder
snow rather than climbing up on top of the snow. But, it
will work more effectively when riding on a trail. A
softer spring setting will allow the front of the rear sus-
pension to collapse much quicker and change the angle of
the track to the snow. A more gradual angle will tend to
raise the snowmobile up on the snow rather than digging
into it.
Many possible variables and adjustments to the rear sus-
pension exist depending on snow conditions, riding style,
and type of terrain. These adjustments can be made to
individualize the snowmobile to the riding style of the
operator.
Manual
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