Viscous

Viscous Fan Coupling

Front Back

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Bimetallic strip in cold closed position Open hot position (blow lamp assistance;-)

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Front covering removed

The liquid inside the unit was totally clear silicone (thanks Lars-Ove for this info) has the viscosity
of treacle. There cannot be any wear on the components, I think that the oil has seeped out of the seals.

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Back view of valve plate behind front cover.

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"Friction" plate behind valve plate. Back cover with "friction" plate removed"

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The bimetallic strip on outside of cover springs outwards as it heats up and
allows the brass pin to move with it out of the cover. This in turn releases the
pressure on the spring valve within the unit and exposes a hole which allows
oil through it from the centre cavity. The unit resembles a clutch assy with
friction disc and plates either side. I suppose the loss of oil from within the
inner cavity where the "friction" disc is, must create the friction which increases
the turning resistance. I'll bring the unit with me to Billing, however as Ian F said
it is a loss of oil which stops the unit from working. Replacement of the oil and
seals is impossible as the unit has to be virtually destroyed in disassembly.

IMHO.............;-)

Coupling Removal

The coupling can be removed and replaced without removing the radiator or cowling.
Use a std 8mm a/f allen key spanner and extend its length using 1/4" drive socket tools.
I taped mine so that I did'nt have to struggle picking them up if they dropped off.

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The other tool is a large spanner for holding the water pump shaft in place. This can be made
from various materials laying around your workshop ;-) It is cranked which will allow the
radiator cowl to push back to give access to the coupling. Alternatively you could buy a std 32mm a/f spanner.

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Position the water pump spanner.The end is long enough to rest on the battery tray so that you don't have to hold it.

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Position the cowl back far enough to give access to the coupling allen bolt.

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Remember the bolt is left hand thread !!

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At this point I must stress that I have not actaully undone the bolt or taken off the coupling, I'll be doing this very
shortly when I get the new coupling.