Bn7 fan

[Jim_Newman]

In its former life (twenty years ago), she was engaged in vintage racing. The cooling fan was reduced to just two blades by employing just one of the standard blade assemblies. Now that she has been domesticated, and especially since she spends so much time in Florida, I'm thinking of reverting to the proper 4 blade set-up. This, as you know, is comprised of two blade assemblies; a front and a rear. They have different part numbers and the mounting hole pattern is different. Several blades are available on eBay but they all seem to have the same hole pattern - the same as the one currently on the car. Hence they are all either front or rear blades. How the heck can I tell the difference? Does anyone in bcfland have a pattern for the holes for the two blade assemblies?

Or maybe I should just ditch the current blade and install something more modern?......or maybe I should just leave it alone?

She does not overheat except in stalled traffic. I'm thinking that the proper fan might be helpful in that situation. (I may go ahead and put in an electric fan). Mainly, however, it's just that it doesn't look right in a road car.

As always, any suggestions or advice, greatly appreciated.

Cheers

 

[Jim_Newman]

Ok. I got it. The 4 hole patterns are simply 45deg out of phase with each other. Kinda weird eh? Why would they not have had the four blades equally spaced about the hub like a right angled cross? Persumably one could use two of the same blade assemblies instead of having two different ones??
Cheers

 

[Bob_Spidell]

It's common for fans to not have symmetrically and regularly spaced blades. 'Texas Cooler-' type fans as well as stainless flex fans have the blades spaced unevenly. There's a reason for it--something about preventing resonance from the blades, maybe to reduce noise or vibration--but I don't know the exact theory. Fans often have an odd-numbered number of blades for some reason as well. It may be that airflow is improved if the blades don't all have to move through the turbulence of the blade before it.

Here's one explanation: https://tinyurl.com/bypfbgc

 

[Keith_M]

I replaced my standard 4-bladed fan with a 5-bladed fan from Denis Welch. The blades are not spaced evenly, which makes it look really weird. Like Bob, I don't completely understand the theory, but the irregular spacing somehow prevents it from making a whirring noise.

It moves A LOT more air than my original fan, and my problems with overheating and stumbling on acceleration after sitting at stoplights on hot days went away after I installed it. Unless you're looking to keep things original, I would recommend using a fan like this instead of trying to find an original 4-blader.

Keith

 

[Jim_Newman]

It's common for fans to not have symmetrically and regularly spaced blades. 'Texas Cooler-' type fans as well as stainless flex fans have the blades spaced unevenly. There's a reason for it--something about preventing resonance from the blades, maybe to reduce noise or vibration--but I don't know the exact theory. Fans often have an odd-numbered number of blades for some reason as well. It may be that airflow is improved if the blades don't all have to move through the turbulence of the blade before it.

Here's one explanation: https://tinyurl.com/bypfbgc

Good article. Thanks.

 

[Leo_Speichinger]

I have a pair of the blades that fit your model (are they all the same?) and if so you are weloce to one or both if you need them.

Leo

 

[Jim_Newman]

Thanks Leo. That's nice of you to offer but I yesterday ordered a Texas Kooler and will go that route instead.
Jim