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English - 51

The task of the crankshaft is to transform the reciprocating motion of the piston to rotation. This requires a

stable design withstanding immense pressure and rotational and bending strain, as well as high rotational

speed. In addition the connecting rod is exposed to large acceleration and retardation forces as it moves

between the top and bottom dead centres. This puts special demands on the bearings that must withstand

quick changes in load. Moreover, the bearing’s roller retainer must also cope with high temperatures and

friction. It is therefore extremely important when servicing to check the roller retainer for cracks, wear and

discolouration caused by overheating.

The crankshaft is journalled in the crankcase on heavy-duty ball bearings. In addition to the journalling

point for the crankshaft, the crankcase acts as a scavenging pump for the fuel/air mixture when this

is “sucked” from the carburettor and is forced into the cylinder’s combustion chamber. The crankcase

must be perfectly sealed so as not to affect this pump function. There cannot be any leakage from the

crankshaft, between the crankcase halves or between the crankcase and the cylinder.

Always replace the sealing rings and gaskets when servicing the crankcase.

7.21 Dismantling the crankcase and

crankshaft

Dismantle the following components to make the

crankcase and crankshaft accessible:

• The starter and air filter.

• The muffler with heat guard plate.

• The spark plug.

• The carburettor.

• The clutch cover and shaft.

• The cylinder and piston.

• The clutch, drive disc cup and flywheel.

Dismantle the 3 screws holding the crankcase

halves together. See figure 67.

Fig 67

Separate the crankcase halves (a special tool is

not required). See figure 68.

The crankshaft has a snug fit in the crankshaft

bearing.

Fig 68

Lift out the crankshaft out of the clutch side’s

crankcase half (a special tool is not required).

Remove the crankcase gasket. See figure 69.

Fig 69

Crankshaft and crankcase

Husqvarna 129RJ Workshop Manual

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