Another Original 2-Blade Fan Takes Its Toll

[Terry, NJ]

Originally Posted by Bill Goddard

OK. Time for my 2 cents - maybe 1 cent. What would the group think of a life limit on fan blades. Maybe 5000 miles. Helicopter rotors are limited by max no. of hours because of the alternating flex problem. I would think you could get 5000 miles on a NEWLY manufactured fan.
Also - if the new sheet metal fans are formed at the base with a shearing burr on the outside radius of the curve there is a real possibility of a crack developing along that edge. I would check a new blade for this burr and file and polish the edge real smooth if I found one.

Bill, I think you're trying to solve a perpetual problem by applying the most draconian answer. Actually, the mod A is the first car I have ever heard of exploding fans on. All my cars and trucks are run to well over 100K miles and I have never had a fan let go. Why are mod As the only cars affected? I should think that the four blade steel replacements should solve this problem, if not, why? My own theory is that Ford made the pitch angles too steep and this cause too much flexing at the higher speeds. This would cause the metal to crystalise and fail. I'm very new to this so maybe I'm talking thru my arse. Let's just convert to stamped steel 4 blade and move on.
Terry

[CT Jack]

What is the point of making a steel reproduction 2 bladed fan requiring welding the blade to the hub? As we all know welding is the primary cause for the original fan to fail. Fact; welding produces small cracks no matter how careful or controlled the process is. The blades on the 2 bladed fan in our engines encounter many millions of cycles of bending loads during normal operation. The most vulnerable place for a failure to occur on a component of this type operating in this mode is at a welded joint. Over time the small cracks (micro cracks) within the weld zone begin to grow as the number of operating cycles continue to increase. Once the cracks reach a certain size and number the welded connection significantly weakens or fatigues to the point where it completely fails causing the blade to break away.
A good quality cast Al 2 bladed fan made in the good old USA is probably the best way to go.
Jack

[Mike V. Florida]

Originally Posted by Terry, NJ

Let's just convert to stamped steel 4 blade and move on.
Terry

My stamped four blade fan let go a few months ago; dented hood, wiped out the radiator, and destroyed the water pump.

[29RPU]

Just a guess, but I'd bet one blade hung on or it was unbalanced and jacked the bushing/shaft.

[windy-au]

A big thankyou to all on this post , as I found 2 cracks in my 2 blade fan when I replaced the radiator today , I have replaced it with a 4 blade fan that I had .
Allan.

[Terry, NJ]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by Mike V. Florida

My stamped four blade fan let go a few months ago; dented hood, wiped out the radiator, and destroyed the water pump.

Why is this? I mean like this is Freakin mysterious! Why do I have cars and trucks that go well over the total mileage of a mod A and I have never had one let go yet. What's so special about a mod A that it is the only car/engine that manages to eat up fans? Why are mod As fan killers?
Terry

[Mike V. Florida]

Originally Posted by forever4

Just wondering how did the fan destroy the water pump?

It went at about 50 mph the fan was so out of balance that the casting shattered away bending the shaft.

[Bill Goddard]

I have never been interested in cars except the model A but I think the fan is more likely to fail because the pulley is not directly supported by a shaft but is cantilevered behind the forward bearing. There is alternate flexing as the fan pulley rotates. I don't know if ANY other cars have this condition. We need a whole new design and we need it now!

[Tom Wesenberg]

Originally Posted by Bill Goddard

I have never been interested in cars except the model A but I think the fan is more likely to fail because the pulley is not directly supported by a shaft but is cantilevered behind the forward bearing. There is alternate flexing as the fan pulley rotates. I don't know if ANY other cars have this condition. We need a whole new design and we need it now!

Don't run with the fan belt tight. I have about an inch and a half of flex between the generator and fan pulley's.

[Glen in Hillman MI]

Originally Posted by Bill Goddard

I have never been interested in cars except the model A but I think the fan is more likely to fail because the pulley is not directly supported by a shaft but is cantilevered behind the forward bearing. There is alternate flexing as the fan pulley rotates. I don't know if ANY other cars have this condition. We need a whole new design and we need it now!

Ford had fan blade trouble well into the 60's. I was in fleet service for over 25 years and replace many ford 4 blade fans.

[Terry, NJ]

Originally Posted by Glen in Hillman MI

Ford had fan blade trouble well into the 60's. I was in fleet service for over 25 years and replace many ford 4 blade fans.

Glenn, With all due respect, I was never a fleet manager and I'm sure you saw more cars a month than I saw in a couple of years. However, that being said, I have been on the road since 1961 (49 years) and I have never heard of this problem with Ford or anyone else. My parents owned all Fords. My father in law owned a small moving company and it was mainly Whites and Internationals. His personal car was a 36 Ford that he used till 1955. My car history began with a 1949 Tudor that I bought for $20, since that "bomb" I had 1 '50- and 3 '51s Then a 54 with a 57 T-bird 312, a 59 Edsel, a 64 Galaxy a 47 merc, and a whole bunch of other stuff.
I spent quite a bit of time around cars in general and I have never heard that anyones's, fans were failing. Not GMs, or Chrysler, nor Ford, or Studebaker, or Packard, or Kaiser, or Nash - Rambler, Crosley, Willys nor International either on it's trucks or tractors, ditto for John Deere, ferguson, Case. This is something you just don't hear about. Since I got into Mod A s, I've heard about it a lot. What is the diference between a 235, 283 chevy, or a 239, 272, 292, 312, 260, and a mod A? Well those engines can rev a lot higher and I never had one let go, maybe some of the cars you were in charge of , the fans let go, but I never even heard of it. Beyond that? It would seem to be in the Mod A's favor, but it isn't. Someone suggested high speed photography to see just what is going on here. Maybe that's the next step. It will take some serious investigation to figure this out. Theories are just unproven opinions.
Terry

[Bill Goddard]

Could it be done with a timing light. Put a dot in a special place and see if it wonders from flexing. Maybe a dot at tip of each blade to start.

[PetesPonies]

It's been explained well in this thread . . but the facts are right before you or the fan. Why are most fan blades riveted? Now if you want to increase the manufacturing process . . proper heat treating could be made to a welded fan . . but for production part that isn't considered viable.

[james.heider]

If someone is going to make a new steel fan, Count me in as purchasing one.
Put me down on the order list.

Thanks Brent

[james.heider]

Brent,

You can put me down for 1 new fan if they go into production.

Jim Heider
Auburndale, Florida

[joncrane]

I have always heard that the two blade fan was stressed when someone attempted to turn the motor a "little bit" when timing with the pin. It was always so convenient to do this, but it stressed the two piece fan. So long as the mechanic used the crank to time the engine, the fan blade lasted.
Just what I heard. Never experienced a failed fan...knock on wood.

[ericr]

I would buy one, that is an item that is long-overdue for quality reproduction, right up there with headlight sockets and lighting switches.

[RonC]

Does anyone know what the status is with the reproduction steel fan?

[Logan]

i know a guy who was listening to a model a motor run under the hood. He took his head out from the engine compartment, then bam.... The two blade fan blade broke off. If he had stayed under the hood for 3 seconds longer, he probably wouldnt be alive.

[Earle]

I would be very interested - up to the $150 - $175 range.

BUT...I'm also aware of some of the technical issues behind the failure history of the original fan design. In simple terms, it's due to high centrifugal forces causing a stress concentration at the juncture of the blade with the hub. From there on fatigue takes its toll as the blades are flexed (however minutely) during operation.

Of course, Henry went for the hollow design (probably to try to keep blade weight down and avoid the fabrication costs of machining, forging or casting the complex "airplane propeller" airfoil shape). But then he had to resort to welding (bad for a dynamic, highly-stressed part) as well as the risk of corrosion developing inside the blade where it could not be seen - and that has happened in nearly every failed fan I've inspected. In many cases the corrosion has eaten through to the outside surface of the blade.

Designing for fatigue loading wasn't a well-understood branch of engineering back then so the best choices were not made as to materials, geometry, load prediction, stress analysis, and thorough testing.

What concerns me about the proposed new fan design is whether all of these factors will be fully taken into account. If the new design is to be a dimensionally-accurate replica of the original, and if it is to have solid steel blades instead of Henry's hollow design, then the centrifugal loading at the hub juncture be increased significantly!

Of course a more fatigue-tolerant steel can be selected but that might not be enough. Altering the geometry to increase the fillet radii at the hub juncture (a common way of reducing stress concentration) would ruin geometric accuracy.

If I and many others are going to spend considerable bucks for the new fan we have a reason to be cautious about exactly how the designers have addressed the real cause of the original failures. It is a real safety and car-damage issue. I've had two original fans fail (after having been magnafluxed as "crack-free".). Thankfully, because I inspected before every drive, I caught them before the crack worked its way completely across the blade.

I appreciate the effort that the new designers are making to FINALLY bring us an accurate and RELIABLE fan reproduction that will pass visual high-point judging. I just hope that they will understand the legitimate concern that many of us have and will provide us the necessary technical details and assurance that the design, fabrication and TESTING are being approached properly.

This is truly a SAFETY issue! Can anyone think of any other part on a Model A whereby you can be killed just by standing alongside the stationary car while the motor's running and everything's operating normally?!