Viscous Fan Function

[redstag]

imported post



From the stag.net archives

Here's the engineering description from the July 1970 issue of
Automobile Engineer:

"A 13 blade, 16-1/2 in diameter nylon cooling fan is driven directly
from the nose of the crankshaft by means of a Holset viscous type
coupling that limits the torque transmitted to the fan to 46 lbf-in
and the maximum speed to 2,500 rev/min. It is retained axially by a
co-axial bolt: the hub of the coupling, in turn, secures on the
crankshaft a Holset inertia type torsional vibration damper, and two
sprockets for the timing chains; the drive is transmitted to each by
a Woodruff key."

There is no mention of a lockup function as used in many other vehicles
to increase the fan speed when the radiator discharge air exceeds a
certain temperature.

Pete

[DJT]

imported post

redstag wrote:

From the stag.net archives

Here's the engineering description from the July 1970 issue of
Automobile Engineer:

"A 13 blade, 16-1/2 in diameter nylon cooling fan is driven directly
from the nose of the crankshaft by means of a Holset viscous type
coupling that limits the torque transmitted to the fan to 46 lbf-in
and the maximum speed to 2,500 rev/min. It is retained axially by a
co-axial bolt: the hub of the coupling, in turn, secures on the
crankshaft a Holset inertia type torsional vibration damper, and two
sprockets for the timing chains; the drive is transmitted to each by
a Woodruff key."

There is no mention of a lockup function as used in many other vehicles
to increase the fan speed when the radiator discharge air exceeds a
certain temperature.


Pete

That's 'cos there isn't one. The Stag coupling is a viscous one (the clue is in the name ). There are othersthat are combined with athermostatic function as well and these can be identified by a bi-metallic spring device built into them, such as BMW, Range Rovers, et al.

Dave

[redstag]

imported post

That's 'cos there isn't one. The Stag coupling is a viscous one (the clue is in the name ). There are othersthat are combined with athermostatic function as well and these can be identified by a bi-metallic spring device built into them, such as BMW, Range Rovers, et al.

Dave

Absolutely. The Stag one is a simple piece of kit that slips at higher speeds.

No need to think of it as anything more complicated.



Pete

[MartinM]

imported post

MartinM wrote:

Anybody got a cheap'n'cheerful means of measuring them both at the same time?

I have

http://cgi.ebay.co.uk/Digital-Photo-Sensor-Tachometer-RPM-Speed-Tool-Case-/130444170367

...not that seller and I didn't get a case, but that model.

Press the button at the side to start measuring, release to stop - then press the memory button on the front and it scrolls through max, min and average for that measurement time.

Comes with three 10x200mm strips of reflective stick on stuff - put some on one fan blade, some on crankshaft nose and measured away.

Very rough measurements -
Engine Fan
1000 850
2000 1800
4000 2470

Looks like my VC is fine

(good piece of kit for setting up idle speed as well)

[martin]

imported post

Hiya Martin, I've just bought one off Ebay, Hong Kong, bit new to Ebay so a little worried, see what happens. Martin.

[GDPR]

imported post

That would be spot on....... due to the size and mass airflow capability of the fan the speed needs to be limited to 2500 or the fan will roar like mad and ultimately break up - simple answer was a fluid flywheel type coupling where the drag is limited to 2500rpm beyond which the fluid shears and drive is lost/finite.

[martin]

imported post

I gather from a few old hands, that some folk have locked up failed couplings, and when the fan gets fast enough, it bows forwards and trashes the rad. :shock: Martin.

[StagnJag]

imported post

Mine was like that when I bought it, the VC had been disabled using an interesting string of washers welded together, the welds broke on the way home and due to the resulting noise I had a real feeling in the pit of my stomach that I had made a big mistake. :?. I wouldn't part with it now, despite the amount it has cost me in the last three years!

Rgds

Dave