Operators Manual

English - 55
Repair instructions
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 oil seal and gaskets when servicing the crankcase.
7.22 Dismantling crankshaft and crank-
case
Dismantling
Dismantle all components so that only the crank-
case and crankshaft remain.
See the respective sections for detailed information
if necessary.
Remove the key from the crank shaft using a tool.
Remove the crankshaft out of the crankcase.
Remove the bearings and oil seal(press fit).
Remove the gasket between crankcase halfs an
residue the base of the cylinder and crankcase.
Inspecting the crankshaft
The crankshaft cannot be reconditioned but must
be replaced if it is worn or damaged.
Inspect the large end of the connecting rod. If
seizure marks, discolouration on the sides or
damaged needle holders are found the crankshaft
must be replaced.