Husqvarna 324HDA, Workshop Manual

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7
Piston, crankshaft and crankcase
504 90 90-01
502 50 18-01
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 cylinder block/crankcase on heavy-duty ball bearings. Over and above acting as a
journal for the crankshaft, the crankcase also works as an oil tray and ”oil pump”. By utilizing pressure variations in
the crankcase, oil/oil mist is forced via a non-return valve and a separate duct up to the valve mechanism. The
crankcase must be perfectly sealed so as not to affect this pump function. Leakage must not occur from either the
crankshaft or between the crankcase half and the cylinder block.
Consequently, always replace the sealing rings when carrying out a service.
Dismantling
Dismantle all components so that only
the crankcase and crankshaft remain.
Dismantle the crankcase half and
crankshaft/piston.
Dismantle the piston from the
connecting rod.
Dismantling
Dismantle all components so that only
the crankcase and crankshaft remain.
Dismantle the crankcase half and
crankshaft/piston.
See the respective sections for detailed
information if necessary.
Remove the piston from the connecting
rod with the help of a gudgeon pin
extractor.
Dismantle the sealing rings and the
bearing on the flywheel side.
The bearing (C) cannot be dismantled.
Clean and check all parts with regard
to wear and damage.
Remove the sealing rings (A).
Dismantle the bearing (B) on the
flywheel side with a bearing puller.
The bearing (C) cannot be dismantled.
The entire crankshaft must be replaced
if it is worn or damaged.
Component Standard Wear limit
Piston diameter 34.970 – 34.990 mm 34.900 mm
Cylinder diameter 35.000 – 35.015 mm 35.100 mm
Play piston/cylinder 0.010 – 0.045 mm 0.120 mm
Piston ring width 1) 0.970 – 0.990 mm 0.920 mm
Piston ring play 1) 0.015 – 0.056 mm 0.120 mm
Piston ring gap 1) 2) 0.100 – 0.250 mm 0.600 mm
Gudgeon pin diameter 7.990 – 8.000 mm 7.950 mm
Gudgeon pin hole in the piston 8.010 – 8.026 mm 8.060 mm
Play gudgeon pin/piston 0.010 – 0.032 mm 0.070 mm
Connecting rod’s gudgeon pin hole 7.978 – 7.989 mm 7.989 mm
1)
Applies to the two uppermost piston rings.
2)
Measure the piston ring gap when the ring is located in lower part of the cylinder.