Rotax 125 MAX - uranusoft.com

Rotax 125 MAX AdjustableVariableExhaust

Introduction:

This information is in addition to the valid repair manual.Safety requirement has to be taken from the valid repair manual.

This information is only for internal usage.Without commitment to advise modifications.

BRP-Powertrain

2010.04.09

Presentation Rotax exhaust valve – only for internal use 3Without commitment to advise modifications

Installationn 1.

Clean the cylinder with brake cleaner and check impulse bore for cleanliness. (visual)


Installationn 2.

Clean the Exhaust valve with brake cleaner and scotch brite and check the total length of the exhaust valve. ( 72 +/- 0,3)

ATTENTION: Stud screw has to be locked with LOCTITE 648


Installationn 3.

Insert the exhaust valve as shown on the picture and assure free movement of the exhaust valve.


Installationn 4.

not correct – gasket interferes contact between valve and cylinder

Apply the gasket on the cylinder and assure metallic contact between exhaust valve and cylinder.

correct – metallic contact between valve and cylinder


Installationn 5.

Apply the valve rod housing to the cylinder and check the exhaust valve for free movement.

In case the exhaust valve piston get caught, check the position of the valve rod housing.


Installationn 6.

Apply the o-ring to the stud screw.


Installationn 7.

Apply the bellow on the valve housing and check the sealing surface for proper sealing. The small hose spring at the bottom of the bellow has to be installed correctly to the groove of the bellow.


Installationn 8.

Hand tighten the exhaust valve piston to the stud screw and adjust a total length of 73,5 +/- 0,3 mm

Torque the exhaust valve with 10 Nm to the cylinder.

10 NM


Installationn 9.

Apply the hose spring with Rotax special tool 276070 to the bellow. Assure free movement of the exhaust valve and make a visual check for the correct installation of the hose spring to the groove.


Installationn 10.

Apply the compression spring to the Exhaust Valve and mount the Valve Cover by means of the spring clip to the housing.


TroubleshootingR.A.V.E (ROTAX ADJUSTABLE VARIABLE EXHAUST)


Engine concept Rotax engine 125 MAX

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125 Max 100cc

5-8% oil2% oil

n Rotax 125 MAX versus typical 100cc kart engines


Engine concept Rotax engine 125 MAX

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Exhaust valve closed till 7.500 rpm

Tuned exhaust pipe in combination with ignition timing

7.500 rpm – 12.500 rpm

Ignition timing

12.500 –14.000

rpm

n Performance characteristic of Rotax engine 125 MAX


1) Exhaust valve

At 7.500 rpm:

Exhaust valve opens through raising pressure in the exhaust system

Till 7.500 rpm:

Exhaust valve closes by compression spring (adjustable)

Low exhaust port timing = longer use of combustion energy

exhaust valve closed exhaust valve opened

High exhaust port timing = shorter use of combustion energy


1) Exhaust valve

The raising pressure in the exhaust system causing the exhaust valve to open.

n Pressure in the exhaust system (schematic diagram)

1 2 3 4 5 6 7 8 9 10 11 12

engine speed (rpm)

pres

sure

exhaust valve closed exhaust valve open


Leistungskurven mit geschlossenem und offenem Auslaßschieber performance graphs with closed and open exhaust valve

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Motordrehzahl [1/min.], speed [rpm]

Motorleistung [kW], performance of engine [kW]

Leistungskurve 2, performance graph 2

Leistungskurve 1, performance graph 1

1) Exhaust valve

Optimal opening timing 7.500 rpm Opening timing

too lateOpening timing too early

n Correct opening timing of the exhaust valve


1) Exhaust valve n Standard setting of the exhaust valve

5 mm = approx. 2 inch

n Adjustment of the exhaust valveè at the race trackè engine must have operation temperatureè accelerate from 5.000 rpm at full throttle

as soon as exhaust valve opens, noise is changing significantly.

è exhaust valve has to be adjusted to open at 7.500 rpm

n Adjustable rpm range for exhaust valve openingApproximately +/- 300 rpm


1) Exhaust valve Re-adjustment of the exhaust valve

… is just necessary if the è cylinder or the height of the cylinder (base gasket) has been

changedè condition of the isolating mat in exhaust muffler has changed

(worn).


1) Exhaust valve –Troubleshooting

n Problem: Missing performance till 7.500 rpm (“bottom end performance”)

n Possible reason: Exhaust valve does not completely close.

n Solution: Check assembly of exhaust valve. Exhaust valve has to touch the cylinder surface in closed position. Metallic noise at closing has to be noticeable.

Exhaust valve does not close completely

wrong

Short use of combustion energy = high exhaust port timing

correctExhaust valve completely closed

Long use of combustion energy = low exhaust port timing


1) Exhaust valve - Troubleshooting

n Problem: Delayed throttle response out of the curve.

n � To the curve: Engine revs 12.500 rpm, exhaust valve is open.

n � Middle of the curve: Engine revs drop to 9.000 rpm, carburettor slide is closed, exhaust pressure drops àexhaust valve closes.

n � Out of the curve: Engine revs 9.000 rpm, carburettor slide open – delayed response of the engine…

Track sector:

1

2 3


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Rotax 125 MAX - uranusoft.com