Stihl BR 550 Technical Guide - Page 6

Technical Information, Engine lubrication, Phase 1, Phase 2 - engine timing

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Page 6 Technical Information 08.2005 1.5.3 Engine lubrication The engine is lubricated in two phases during each revolution of the crankshaft. Phase 1 The piston rises to the top dead centre. Phase 2 The piston descends to the bottom dead centre. The increase in volume in the crankcase produces a vacuum. From the intake duct (1), the air-fuel-oil mixture is drawn through the bypass port (2), valve train (3) and timing gear (4) into the crankcase (5). The oil contained in this mixture lubricates the crankgear, timing gear, valve train and cylinder wall. Excess pressure builds up in the crankcase due to the decrease in volume. The mixture of air, fuel and oil in the crankcase is returned to the intake duct via the timing gear, valve train and bypass bore. This rewets the lubrication points. TI_08_2005_11_01_02.fm

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Page 6
Technical Information
08.2005
TI_08_2005_11_01_02.fm
1.5.3
Engine lubrication
The engine is lubricated in two phases during each
revolution of the crankshaft.
Phase 1
The piston rises to the top dead centre.
The increase in volume in the crankcase produces
a vacuum. From the intake duct (
1
), the air-fuel-oil
mixture is drawn through the bypass port (
2
), valve
train (
3
) and timing gear (
4
) into the crankcase (
5
).
The oil contained in this mixture lubricates the
crankgear, timing gear, valve train and cylinder wall.
Phase 2
The piston descends to the bottom dead centre.
Excess pressure builds up in the crankcase due to
the decrease in volume.
The mixture of air, fuel and oil in the crankcase is
returned to the intake duct via the timing gear, valve
train and bypass bore. This rewets the lubrication
points.