Technical Cut down flathead gen mounted fan & how to balance it?

You beat me to it. We were both going the same RPMs but I had farther to go.

 

Pretty sure that would be 3000 rpm, too.

 

Which is heavier? A pound of feathers or a pound of lead?

 

Actually if a man is in a real hot rod all you see is tail lights so you would never know if it had an electric fan.

 

Speed an RPM are not at all the same. Cutting away the tip=shows down the speed of tip at any same RPM.

Two things about fan balance;;;; There is spin balance*,but that is not the same as air load balance* ( blade pitch )
Blade that is bent in any way other then how factory did it new=that with put it out of draw pitch//one blade trying to bit more/or less air then another= vibs an often a odd sound too. This shows up often in fans that have been in a crash and were only a tiny bit bent or bent back after.
A jig can be made to check pitch,by hub clamped in vise an jig clamped to vise also,turn one blade at a time to jig/every one should match jig angle{pitch}

One more thing::: Don't be lazy ,build a FAN SHROUD that fits 360* with a max of 1/2 in gap too blade. Remember ,most factory fan's turn at 1/2 the RPM of crankshaft.

 

Which ones spin at half?

 

The only engine fans that run at crankshaft rpm, are about 12 in. around an under. Factory spec. are some times hard to find. So just giving a rule of thumb.< there are exceptions to every thing.
If you check crank pulley size,to fan pulley size,,that can tell you. Remember;it's circumference to circumference///not diameter to diameter.
Some old engines,that did not turn many RPM,ran bigger fan,right on the end of crank .

 

All the Pontiacs from '73 up had water pump pulleys smaller then the crank pulley to overdrive the fans and pump. And earlier Pontiac's had smaller water pump pulleys on A/C cars the non-A/C cars to speed up the water pumps and fans. Never have I seen a water pump pulley twice the diameter of the crank pulley.

 

I'm of the mind reading this fan thread to having a few random thoughts came to mind.

First, I do recall trimming a fan that was missing a chunk of one tip. Can't recall why it was damaged, just that it was, I did, and I do recall painting all the tips red thinking Safety first!

Interesting. And most confusing. Because the distance being shorter and speed being relative to distance, I'd think that would equate to faster? Then again I think, sure glad there isn't going to be a test.

Remember, all random thoughts...but what if you did. Blow your mind right! And if I think much more about it I won't get anything done.

And would cutting down the fan matter at all? Turns out it does. But what if you push air out instead of pulling air in?

Probably not a problem by the sound of your approach to doing it. Then again, how fast is it going to spin?

 

If it helps, fellas. My plan worked and the fan has no more vibration than a stock one.

 

Actually the speed increases with diameter increase. At least on the tips of the fan blades. This is actually a bit of physics that some of us think about in engine theory. Some of us sometimes look for a small journal crank for an engine that is going to spin higher RPMs. Smaller journal = less bearing speed.

On a cooling fan if you shorten it up you are decreasing the speed on the tips of the fan blades. This on most of our engines actually makes little difference, we have a lot of wiggle room if the rest of the cooling system is up to par.

@dana barlow I have actually had a fan fall off the bench and tweak it enough to make it a little noisy. Not enough to see it but you can hear it and pick up the difference in *pitch/balance by laying your hand on the shroud.

*pitch in this instance is not angle of the blade. Sound instead of angle.

 

I can guarantee that Ford sold an electric fan that bolted on a 59A series engine. I sold this one to a guy up in Maine 4 years ago and I'm pretty sure he was putting it on a hot rod.

 

I run electric fans all the time. For me a hot rod is supposed to be fast and a mechanical fan costs torque to turn.

Now sitting still at a car show a mechanical fan looks cool as hell. But it is like I said, you cannot tell from my tail lights what kind of fan I am running.

 

Yeah then you would know, heavy side down, it aint rocket science.

 

I’m wondering if he meant speed. - 201 kph by my maths. or about 125 mph…..
My real question was why does an original fan hit the original radiator hoses and need cuttingdown thereby lessening air flow ?
Sounds like a quick fix instead of a proper one ?
With no pictures it is hard to say, but maybe wrong hoses.
When I bought my flathead, I had a similar problem, but just altered the hoses.
Although for the last 5 years I haven’t actually run a fan at all………
( I don’t run hood sides, so get a bit of air cooling and try to just keep moving forward and don’t back up much)

 

So I must have missed it or forgot, how did you mark where to take off, and what was used to remove the blade material?

 

First a made a template out of card stock of a full length blade so it included the curricular portion of the hub. I then shortened the template on the hub side.

I then laid the template on the blades and scribed out cut lines.

Using a fine toothed blade on a band saw, I then carefully cut the blades.

I then checked it with a gen hub idler bracket I had made previously. The blades stopped at random places indicating they were relatively in balance.