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

I had at trim off some length from the blades of the gen mounted flathead fan in order to get it to clear the rad inlets. I made a templet and use it to trim each blade the same.

I'm sure it's now unbalanced (not sure if they ever were- LOL).

Looking for ideas on how to check the balance. The hub is too deep to use one of the lawn mower blade balancers. I've read before of using a nail.

I'd assume a machine shop could check for this as well or is that not necessary?

I just don't want it to come apart due to vibrations of being unbalanced.

Thanks,

 

Before you do any cutting, check the fan to see how balanced it already is.
Be sure to have it magnafluxed for microscopic cracks and flaws also.
How old is the fan?
Is it NOS?
Has it been consistently "in use" since it was made?
Is it rusty?

 

How old? I believe the hub size makes it a '36. Not NOS and yes it's rusty. I do have some NOS fans that I chose. not to cut down. Maybe I need to rethink that.

As far as usage, not sure. I've had it for at least 20 years.

 

Yes indeed! There is no doubt that its safer to cut down
a NOS fan as the metal has never been work hardned and developed cracks
due to flexing and rust. It's a good idea to rethink your strategy.

In 1972 I had an old metal fan of a 50 Ford truck fly apart without warning while
I was standing next to the front fender giving it gas to warm up the engine.
WHAM! , a blade went into the radiator and through the hood. That made me a believer.
Besides, what are you saving your NOS fans for? Will you ever use or sell them?
Don't take the chance. If it doesn't kill you, you will be scarred for life.

Can you figure out a way to adapt a FLEX FAN or a fiber glass fan? Or, mount the fan on the crankshaft? This has been discussed on Fordbarn.
https://www.google.com/search?q=fle...512j0i512l3.2761j0j4&sourceid=chrome&ie=UTF-8
https://www.google.com/search?q=fan...9i57j33i160.7593j0j4&sourceid=chrome&ie=UTF-8

 

Haha. Good point. Not sure. They just followed me home along the way.

 

Consider using an electric "puller" fan behind the radiator.

 

Can't do it. No electric fans on a hot rod

 

You could try hanging it on a nail on the wall like a lawnmower blade.

 

Use a simple cone type lawn mower blade balancer. https://www.amazon.com/Stens-750-04...wn+Mower+Blade+Balancer&qid=1644770368&sr=8-3

 

Cut the fan down on my 32. I cut it just a bit long and put it in a lathe and trimmed off the ends until all were the same length. Take very fine cuts on the lathe. No balance problems, over 75000 miles.

 

I have one and couldn't think of a may to mount it since the hub is too wide. I can make a metal circle with a hole dead center to mount on the balancer.

 

Why are you assuming it's unbalanced after trimming? Was there a riveted or welded-on weight on the end of one of the blades you removed? If not, and you trimmed exactly the same amount off each blade, it should still be balanced however good it was to start with.

I swapped the flex fan on my avatar for a clutch fan a three years ago (primarily to reduce noise, but it did improve cooling) and had to reduce the new fan overall diameter by 1.25" for clearance. I did the same thing you did; carefully removed the exact same amount off each blade. I've had zero balance/vibration issues.

 

I just made a fixture to mount to the hub of the fan that will allow me to mount it on a lawn mower blade balancer. Let see how this works out.

 

I would prop the brushes up off the armature, and then spin the whole assembly by hand. Make note of which blade hangs lowest a each stop. If it's always the same one, grind a hair off the end and try again. If it never stops in the same place, I would think it's pretty close to balanced.

 

Ah, I like that idea.

 

Late to the party, but what @alchemy said.

 

I'm digging this thread back up because I am having fan size issues which indicate I need to run a SMALL fan (like, <13") on my build. What did you end up doing to solve this? Did you figure out how to mount a universal fan to the ford hub by chance or did you cut a NOS one?

 

Here's what I did: I made a template of a fan blade and then using the same end shape, I chopped the template by 2".

I then laid out the template on each blade and cut them with a band saw nice and slow.

Using an idler pulley set up made from an old generator, I "balanced" the blades in vice. I made a mark on one blade and keep spinning it to see where the marked one would land. It never landed in the same spot, so I'm assuming it's good to go.

I've had it on the car for a few months and no issues so far.

I did use an NOS fan for this.

 

If the pieces you removed from the blades are identical, the balance is not likely to be any worse than it was before.

 

I had hell with a fan on my 32 5W. It was modified from a crank mount to a gen mount. It shook like hell. I made a test arbour to spin it. It was just some bearings on a shaft with a flange. I could spin it with a drill. It was so far out I switched to a late model fan. I made an adapter that would bolt to the gen and the fan and extension would bolt to that. The drawing is incomplete as it was just a sketch for machining. The stainless fan still shook a little. I put the plastic fan on and it ran smooth and really moved some air.

 

This is a blue law in your state? Or your club doesn't allow it or you are showing or racing in some class that requires a mechanical fan?

Sorry I just could not resist.

I would install it and run it. See how bad it vibrates. If its a real shaker you can balance it the same way you balance a motorcycle tire. Set it up so that spins freely and give it a spin. Mark the bottom blade. Now spin it again. The heavy blade will land on the bottom again, either add a little weight 180 opposite or remove a little weight from the blade on the bottom.

 

These little issues are only difficult if you make them difficult. Think before you cut and then be exact on each blade after the first one. Move on to next problem. I only get anal when working on Helicopter blades.

 

Some folks call it a Kaiser blade, uh huh.

 

This feels like words to live by.

 

Hahahaha....

 

You could number each blade and each cut off piece. Then using a food scale weigh each cut off to see if they are close to the same. Any light ones mean the same numbered fan blade would need some more removed to equal the others.

 

Hahaha. To your point, measuring twice, cutting once worked out perfectly.

 

You might consider having a machine shop build the adapter I showed. You end up with a balanced, lighter, brand new fan. It pulls more air and is quieter. You can pick the hub length.

 

I agree, real hotrods dont have elecric fans

 

If the fan was balanced to began with and you “ carefully / accurately “ remove the same from all the blades it should remain balanced very closely to OEM specs . Question “ if the blade is spinning at 3000 RPMs at the hub center , how many RPMs at the blade tip on a 14 in fan blade ? “ This May shock you !