I'm trying to get a clear answer on this, but asking on the Facebook groups isn't a great place to get info. I've tried and was actually laughed at! I have a '28 Sport Coupe and it has a 2 blade fan. I'm seeing 4 blade and two blade online and I'm wanting to know....which one is correct for my car and which one is the dangerous one.
Proper Fan For '28
- Thread starter CatMan1
- Start date
A clear and simple question that deserves an appropriate answer...your car came with a 2 blade fan. I would strongly recommend that you purchase a cast aluminum 2 blade fan and not be tempted to use an original steel 2 blade unit due to potential structural failures/metal fatigue/cracking. 4 blade fans will work fine, but were never installed on Model A's as original equipment. They were original equipment on Model B engines used in trucks.
If your fan is two bladed and a magnet sticks to it then it is original steel one.. Then it is the dangerous one.
The Reproduction two blades are aluminum so magnet does not stick.
Do not rev or run engine when anybody's face is near the original fan blade.
When they come apart they can go right through the hood or radiator and keep right on going.
In 1962 my fan made a 3 or 4 inch hole in hood and went off into a Sugar Beet field.
The Reproduction two blades are aluminum so magnet does not stick.
Do not rev or run engine when anybody's face is near the original fan blade.
When they come apart they can go right through the hood or radiator and keep right on going.
In 1962 my fan made a 3 or 4 inch hole in hood and went off into a Sugar Beet field.
Last edited:
Joe K
Well-known member
The original 2 blade "two piece" (welded) fans were and are a problem with cracking. Ford, even during the Model A Era, tried to correct the issue by making the blade pressings to be 2/3 length and "overlapping" the blades at the pulley center. A concession to "centrifugal force" and capturing water between the blade pressings perhaps.
Four blade fans CAN be a solution for the safety minded. But even they have a tendency to crack between bolt/rivet holes and a blade fly off.
Some with a reluctant radiator might be tempted to use a 4 blade to "move more air," but in reality they don't, and the forward motion of the car actually moves more air through the radiator than ANY kind of fan at any speed other than sitting still.
Best is the original two blade "style" done in aluminum.
Early production of the aluminum fan suffered a bit in the "taper" where it attaches to the water pump shaft. People had various solutions to making the mechanical attachment - and making sure it was "fully seated." New available production (when you can find it) appears to have solved the taper issue.
Joe K
Four blade fans CAN be a solution for the safety minded. But even they have a tendency to crack between bolt/rivet holes and a blade fly off.
Some with a reluctant radiator might be tempted to use a 4 blade to "move more air," but in reality they don't, and the forward motion of the car actually moves more air through the radiator than ANY kind of fan at any speed other than sitting still.
Best is the original two blade "style" done in aluminum.
Early production of the aluminum fan suffered a bit in the "taper" where it attaches to the water pump shaft. People had various solutions to making the mechanical attachment - and making sure it was "fully seated." New available production (when you can find it) appears to have solved the taper issue.
Joe K
All good answers! Thanks! I need to stay off Facebook. I'll have to check mine to see if it's steel or aluminum. I think it's stock and it came with the car when I got it 4 years ago. I suppose I've gambled long enough! I'd better be ordering one before driving season comes! Here in Iowa it's supposed to be 57 on Sunday and I was considering getting it out.
johnbuckley
Well-known member
I think there are now back in stock with some of the vendors; try Snyders or Mike's Affordable
Canton_Model_A's
Senior Member
FWIW, here is the link to Snyders. They are back in stock, I am going to replace my 4-Blade (Unknown vendor, was on car when I purchased) to the as equipped 2-Blade.
https://www.snydersantiqueauto.com/product.htm?pid=979278&cat=41698
Last edited:
Joe K
Well-known member
The original Ford 4-blade fan had the blade pressings "riveted" to the center spool. A later 4-blade exists nearly identical which MAY or MAY NOT be Ford - but instead have small "bolts" (with lock washers) to attach the two blades pressings to the spool. This later bolted 4-blade was used by the major car makers until the 1960s. The Ford spool was "spun" or a turning while the later spool was "turned" from a solid casting and the bolts "screw into" the casting with no nuts.
A later "two blade" Model A fan was commonly available from the likes of JC Whitney and others (I expect Western Auto) and was a single blade pressing identical to the four blade pressing - but this fan only used the one pressing. The same four bolts. And the same failure mode of cracking between bolt-holes.
Again - aluminum cast blade is proven so far as "safest."
Joe K
A later "two blade" Model A fan was commonly available from the likes of JC Whitney and others (I expect Western Auto) and was a single blade pressing identical to the four blade pressing - but this fan only used the one pressing. The same four bolts. And the same failure mode of cracking between bolt-holes.
Again - aluminum cast blade is proven so far as "safest."
Joe K
Clem Clement
Well-known member
I've asked before and ask again:
I wish someone smarter than me would sit down with a trusty slide rule and a tall glass of liquid courage (Gin) and calculate the number of flexes the metal goes thru in the fan's lifetime. The compare that with what the advertised strength of the fan is. I'm betting the fan passed the flex limit a bazillion+1 times ago (include the corrosion effects of the surface rust in-between the folded blades"
My view is to make an original fan part of the tool kit. A judge can inspect it and say "present"
Let's wait for the coming new balanced aluminum fan,
Clem Clement: In tears about the loss of the airmen and the passengers yesterday.
I wish someone smarter than me would sit down with a trusty slide rule and a tall glass of liquid courage (Gin) and calculate the number of flexes the metal goes thru in the fan's lifetime. The compare that with what the advertised strength of the fan is. I'm betting the fan passed the flex limit a bazillion+1 times ago (include the corrosion effects of the surface rust in-between the folded blades"
My view is to make an original fan part of the tool kit. A judge can inspect it and say "present"
Let's wait for the coming new balanced aluminum fan,
Clem Clement: In tears about the loss of the airmen and the passengers yesterday.
Y-Blockhead
Well-known member
FWIW, here is the link to Snyders. They are back in stock, I am going to replace my 4-Blade (Unknown vendor, was on car when I purchased) to the as equipped 2-Blade.
https://www.snydersantiqueauto.com/product.htm?pid=979278&cat=41698
Thanks for that info. There is a lady in our club that I work on her '29 PU. Every time I work on it I find myself ducking to one side, just in case... We are going to have a "chat" next time I see her.
Canton_Model_A's
Senior Member
Just as long as the chat isn't with a fan deciding to re-locate itself through the hood
Y-Blockhead
Well-known member
I just ordered her a new aluminum fan from Snyder's, she just doesn't know it yet.
Canton_Model_A's
Senior Member
I just ordered her a new aluminum fan from Snyder's, she just doesn't know it yet.
Groundhog day special.
Not sure where u are at Y, here in Canton, I will get my 'goodies' from Snyders tomorrow. (Fan, Spreader, Shackles, drill bit), I ordered them today -Edit-
I looked back, I see you are in Cali
Bob Bidonde
Well-known member
This is my analysis of how the original propeller fan cracks. Cracks occur where there is a tension stress field in the metal. Cracks initiate usually where there is a stress riser in the tension field such as change in the metals cross sectional shape or at inside corners and changes in metal thickness. With these thoughts in mind, here is a look at the Model A's original 2-blade propeller fan in action.
When the propeller spins, there are centrifugal forces on the blades acting outward which produces tension fields in the blades. Also, the propeller's shape of its blades tends to pull the car forward, but the car's mass is too much so the blades bend adding a lot to the tension fields in the metal. The tension field stresses concentrate at the hub of the fan where the fan's shape changes. The bending and centrifugal forces are recurring for hundreds of hours (millions of revolutions). A crack initiates first at the leading edge of the fan's blade with the highest stress concentration. The crack grows slowly at first, but it accelerates as the cross sectional metal of the fan becomes less and the stress at the crack tip increases substantially. When there is not enough metal left at the crack to react the forces acting on the cracked blade, the blade departs with a very high amount of kinetic energy like a bullet. The energy in the flying blade is 1/2 times its mass times its speed squared! It is enough energy to pierce the hood and the radiator. God forbid if the hood is open and a bystander is in the way. The impact of the blade may be lethal! I hope this analysis scares those who are still running original 2-blade fans.
When the propeller spins, there are centrifugal forces on the blades acting outward which produces tension fields in the blades. Also, the propeller's shape of its blades tends to pull the car forward, but the car's mass is too much so the blades bend adding a lot to the tension fields in the metal. The tension field stresses concentrate at the hub of the fan where the fan's shape changes. The bending and centrifugal forces are recurring for hundreds of hours (millions of revolutions). A crack initiates first at the leading edge of the fan's blade with the highest stress concentration. The crack grows slowly at first, but it accelerates as the cross sectional metal of the fan becomes less and the stress at the crack tip increases substantially. When there is not enough metal left at the crack to react the forces acting on the cracked blade, the blade departs with a very high amount of kinetic energy like a bullet. The energy in the flying blade is 1/2 times its mass times its speed squared! It is enough energy to pierce the hood and the radiator. God forbid if the hood is open and a bystander is in the way. The impact of the blade may be lethal! I hope this analysis scares those who are still running original 2-blade fans.
