Hi Brian, interested listers in the Cooling/Electric fan/metal fan thread
:
Picking up where we left off a few weeks ago, I finally got the Jensen
GT restoration Project going Saturday, and got the water pump, and
factory stock mounted viscous fan pulled.(a whole day-that's another story).
From our previous conversations, I was especially curious about the
viscous fan. You mentioned a Volvo Viscous fan option exploration, and I
mentioned the Jensen-Volvo connection, so who knows?
The Fan fitted to the GT (Lotus 907 Engine) is 17" diameter, has 13
blades, and is 1 1/2" 'thick'. The plastic blades and metal frame
center (circumference) are mounted with four bolts onto a cast 'round
hub'.The fan sub-unit weighs 1 1/4- 1 1/2#.
The cast metal hub is 5" across and weighs 2 1/4 +#. Inside the hub is
pressed a bearing-the inside diameter of the bearing race which is press
fitted onto the waterpump shaft is .93" (go figure).
The Viscous fan works by the air vanes and bearing 'slipping' as the
waterpump shaft spins faster than even the crankshaft, and this is an
engine with a 7000 RPM redline in non-race stock form.
As a side note, which may have some merit, aircraft propellors are
ineffective above 2800 RPM, at that speed they cause the air to cavitate
and therefore on turboprops ,propellor govenors limit blade/prop speed
to 2800 rpm. I wonder if the viscous fan limits itself to say @ 2500RPM
- the air resistance keeping the fan 'moving air'.
Assuming one could make an adaptor- and our objective is to reduce
crankshaft vibration, I have thoughts/questions about adding 3 1/2 - 4#
of weight on the front of the TR4 crankshaft. I would suspect that the
original metal fan and hub only weigh together @ 2#. Clearly the design
is more 'balanced' than the old TR4 metal fan.
I also saw two TR6 engines with the plastic fans. One was red and one
was yellow and they are certainly light and wouldn't create the weight
problem of the imbalance original TR4 metal fan, and certainly weigh
much less than this viscous fan.
I know the earlier Jensen-Healey Roadsters used fixed plastic fans,
maybe the same as the TR6, however, the GT viscous fan was larger in
diameter (17") as well as being viscous, and cooling (a problem on the
aluminum 907's) was improved. Later cars also came stock with oil coolers.
I'm more comfortable than ever with my decision to go electric with the
TR4, and in fact will do some research about eliminating the Viscous fan
on the GT and adding an electric to that car as well. I know the
electric fan in pusher mode is an option that has been chosen by many
J-H's, but usually in addition to the stock fan.
If you come up with any info on the Volvo fan- please share!
Sherman
Sherman D. Taffel
Columbia, MD
TR4 with metal fan imbalance >3800RPM
electric conversion in the 'wings'.
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