ORIGINAL FAN BLADES

(stolen from Dale Clinton's Model A board)
Here's the link
I've also added a copy of Bob Murphy's article on Late 31 fan blades that appeared in the September-October issue of MARC NEWS. Thanks Bob!

Vince has written some more on the issue, and granted me permission to use it. The page is regards to repop water pump shafts, with specific attention to the fan blade taper. You'll find it on the (repop vs orginal page). Thanks again to all the contributed....jm

We start with Vince Falters post:

"Here's the story on the (in)famous dreaded original two blade steel propeller fan, and the later improved Holley design fan. The original design used by Ford from 1928 to mid 1931 consisted of a two piece stamped steel construction as shown in the first pic. Each thin piece of stamped steel formed the front of one blade and the back of the opposite blade. The two halves were seam welded around the perimeter and had an odd ovelap condition where they came together at the front of the hub.

The fatigue cracking usually originates at the blade root where the overlap is visible in front view, though ultimately either blade can crack. In the first pic that point is visible at about the 5:00 position from the centerline. These early style fans crack there for a number of reasons. First, the pieces are thin steel stampings with the raw sheared edge located in cyclic tension at the point of highest stress at the blade root. Second, the two piece seam welded construction allows moisture and rust to form inside the blade halves, and this can both weaken the fan and cause mass imbalances which increase the stresses at the blade roots and hasten the crack initiation and failure.

The two pics below show the Holley design fan, which was used from mid 1931 until 1934. At a glance it looks like every other fan, but it is different and much improved and was Ford's fix to the fan cracking which was becoming apparent by that point in time. These fan blades are made from a single piece steel stamping. The stamping is about twice as thick as the early one, is made from a tempered high carbon steel, and is tough like a quality shovel head.

You can see in the pics how the improved one-piece stamping is wrapped over itself in the center 5 inches of the fan, and how the leading edges at the root consist of a radiused surface formed by the hemmed heavier gauge steel, and how there are no sheared edges or sharp corners anywhere in the critical center five inches of the fan to act as stress raisers and crack initiation sites. The third pic shows the back side of the late fan blade and how the doubled over metal is electric welded about 2-1/2 inches out from centerline. This is how the critical blade-root zone is designed for increased strength and protected against fatigue failure. I have seen many cracked early style fans, but have never seen or heard of a failure on this improved style. Additionally, since it is a one-piece blade construction, there is no place for the moisture to form rust and imbalances out on the blades where it would affect the fatigue life, though rust can form on the inside of the hub area in both the early and late styles. Now that I've shared all my secrets, I expect a run on all the late style fans at swap meets. I am not aware that the facts above have ever been published in Model A circles, though they are commonly known amongst the Model B and Early V8 era crowd." Vince Falter

AND HERE IS Marco Tahtaras's COMMENTS:

"My primary focus is on the potential weaknesses of the early fans.

1. The early style fans were double layered throughout as mentioned. The two layers were electrically roll welded around the perimeter. This seam is clearly visible in the first photo. It is apparent that the roll weld could not get all the way to the center hub. This left a small area at either side of the hub front where the two layers weren't joined. This allowed the layers to flex independently at the ends of the seam. All the stress is confined to these small areas as the weakest point. If you find one of these fans on it's way to breaking loose you will see a gap between the layers at this point from the two layers working against each other and stretching.

A fan that has not reached this point of self destruction can be substantially strengthened by simply TIG welding the seam closed from the end of the roll weld to the center of the hub. This not only strengthens the fan at the hub by eliminating the independence of the layers, but is not visible when installed if done well.

2. Also as mentioned the early fan is prone to corrosion between the layers. This generally becomes evident on the rear side 2-3" from the outer ends. Rust grows between the layers and bulges the rear side making the fan thicker in these areas. Again as mentioned this can, and generally will, cause a serious imbalance between the blades. I've seen attempted corrections to this but personally avoid ANY fan that has begun to expand from internal corrosion.

3. Many two blade propeller fans (including the later type) have been bent from "backyard mechanics" using the fan to turn over the engine by hand and too lazy or ignorant to use the hand crank. This makes the blades uneven and in some cases changes the pitch of one of the propeller blades. This will make the two blades pull against the air at different rates at higher speeds causing an imbalance.

The fan MUST pass the "string test" that proves the leading edges of the blades are on a perfect centerline with the shaft hole. Also, the fan must spin with both blades on the same plain. Running your car at idle will allow you to see if both blades follow in line or on the same plain.

The later type fans (introduced early 1931) are not only stronger, they eliminate the internal rust problem at the ends of the blades. They also reduce the weight at the ends of the blades which reduces stress somewhat. These were commonly sought after when I was a kid in the hobby in the early 70's, and continue to be to some extent.

There will be a few that will respond to these posts and say "They aren't safe!" and claim the metal fatigue is absolute. I don't really need to change anyone's opinion since I am in need of one more good early type fan and certainly don't need any more competition!" Marco Tahtaras

AND FURTHER COMMENTS BY Vince

"Actually, the leading edge of the blades are not in a true plane. They are obviously symetrical, but the outer tips are forward of the hub slightly, forming a very slight 'conical' shape when spinning."

Here's some photos of a fans that self destructed :

Here's Bob's Article...

"I am sure many of you, like me, have heard about the use of the late '31 fan blade on the driver cars to avoid the problem of the broken fan blade going through the radiator or hood, or maybe even both.

For those of you unfamiliar with the late '31 fan blade, it looks much like any other blade except that instead of being a sandwich of two pieces of metal from one end to the other, the layer on the side of the blade toward the engine is terminated about three-fourths of an inch on the outboard side of the pulley. It is very easy to spot, just look for the straight edge of metal that ends on the underside of the fan.

It is considered to be a superior fan to the earlier fans, so much so that the Judging Standards Committee has permit- ted the late '31 fan to be used with any year car. I have even seen these fans for sale for as much as $150 since they are so good!

On the way home from St. Louis last summer, I found that even with an "indestructible" item such as the late '31 fan blade, Murphy's Law can still come into play!

While running along about 50 mph, I heard a tinny clatter from under the hood that lasted only briefly, but enough to convince me that I had better stop and have a look. Sure enough, a piece of the fan blade was lying in the engine splash pan, and a hole in the radiator was leaking profusely. The photographs tell the story. The fan not only punctured the radiator, but also got tangled with the fan belt and the generator pully and got them too.

Mike Herring, one of the Sycamore "A" members on the trip, had a spare fan. I had a spare generator complete with pulley and by pinching the radiator tubes together to slow the leak, I was able to come on home with no further problems (I might mention that I, too, now have a spare fan in my car).

The moral of the story is, "keep a watch on your fan blade, even if it is a late '31 blade."

In my case, I permitted myself to be lulled into a false sense of security by the "indestructible" late '31 fan blade, and neglected the periodic blade check for cracks. Result - bad news.

I still feel however, that there is enough of an advantage with the use of the two-blade fan that it is worth the trouble. Not only is it a requirement to qualify for a blue ribbon car, it is also convenient when it is necessary to remove the water pump. With the four-blade fan, I have always found it necessary to remove the radiator first. Some folks feel that the four-blade fan is better for cooling, but I have always used the two-blade fan and solved my cooling problems by use of a good radiator. I have never been convinced that the extra air movement of the four-blade fan really did any good anyhow, especially since it actually presents an additional load, and thus generates more heat (there ain't no free lunch!).

Although this is the first time I, personally, have had a problem with a fan blade, and have driven many thousands of miles with a late '31 blade, I have begun a practice of including a close check of the fan in my usual driving checklist. This is a little more bother, and negates the advantage of the late '31 blade in my mind, since if I am going to have to bother to check it, I can just as easily check an earlier blade as I can a late '31 blade. In fact, I now have an earlier blade on my car, as I haven't yet repaired my late '31 fan.

With the fan blade check now a part of my driving inspection routine, I expect to drive many more thousands of miles without any "fan blade through the radiator or hood" problems." Bob Murphy

Thanks for letting me reproduce the 'definitive' work on original Model A fans.

Page designed by Jim Mason July, 2007