4 blade fan

Pros & Cons, ...it used to be that 2-blade fans were dangerous before reproduction fans came on the market. 4-blade fans were introduced by Ford for AA applications where air was needed to cool the radiator at slow mph speeds. Tests have shown that a 4-blade will set up a wall of air in a passenger car that actually slows down the frontal flow of air when driving over about 30 mph. Use a 4-blade if you don't have a repro 2-blade fan, --or if you are only driving at slow speeds with a marginal radiator.
 
My recommendation, use a new two blade fan with engine side pans. If you have a good radiator and grease less water pump, your good to go. There is a reason Ford did things.
 
I have seen some repro two blade fans with as much as 7/32 run out in the blade tips. Before installing one check the run out and balance.
A four blade fan also causes much more work if the water pump needs to be removed.
 
Fans need to be inspected on a regular basis. If your fan has no sign of stress cracks and is tracking properly then if it is not asked to spin faster than Ford intended there should be no reason to worry.
 
About thirty years ago we had a fan blade break off at 45 mph. The damage it did would cover the cost of many new, high quality, correct reproduction blades. Prior to breaking, it showed no signs of having a problem. Like cracked tires, an 88 year old plus two blade fan is an accident waiting to happen. I treat our Model A like our daily drivers. Safety first or don't take it out.
 
I've been running a 4 blade for a long time. I installed it because I had it hanging around and noticed a crack in the original 2 blade. Purchased a new 2 blade a while back but haven't gotten around to install it yet. The 4 blade works just fine for me and as far as I know they don't have a history of breakage. Maybe this year it'll get changed, maybe.
 
The four blade fan was introduced in 1933 and carried part number 46-8600. It was continued into 1934. It was the dealers replacement fan for 1928-1934 four cylinder cars (see the Green Bible and/or http://www.fordgarage.com/pages/model46fans.htm) and that is the reason there are so many around. They too have been known to throw a blade. I think this was problem because people used the fan blades to turn the engine over when working on it. Once they were bent and straightened there would frequently be a stress riser and it would eventually grow until the fan blade failed. It is the fan that I always use but if starting from scratch I would buy one of the 2 blade, cast, aluminum fans. I would not buy one second hand (unless I knew the seller) since a lot of them had problems. I would buy from a company with a good reputation and if it had a problem return it.

Charlie Stephens
 
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The repro 2 blades are lightweight and nicely balanced though some may have better finishes than others.
 
An EXPERINCED mechanic knows how to turn an engine a FEW degrees, with the fan blade, without DAMAGING it! SOME just don't ADMIT IT--LOL
Bill Trick
 
My old worn 1961 engine [ that doesn't leak or burn anything] with 45# compression can be turned [ with sparklers removed] with just a tug on the belt.

I do have to admit that I certainly have turned engines by grabbing the fan. But as Bill points out, there is a way to do it and a few ways not to do it. [ smiley face]
 
I run Ford 4 blade fans on my cars.

I inspect them every so often.

DO NOT use a fan that has rust pits or has been damaged or straightened.

I WOULD NOT run a repo 4 Blade fan. Most are poorly designed and made and the blades will flex and fatigue.

The repo 2 blade fans seem to work well but some of our club members have had trouble with them becoming loose on the shaft. Either they were not tightened properly or the taper in the fan was not correctly machined.

As stated before, I would NOT buy a used aluminum fan. Some of the early ones were not machined correctly.

The original Ford 2 blade fans are for display only. They will rust between the 2 layers and crack and brake.

Again, JUST MY OPINION.

Chris W.
 
When a four blade becomes a three blade, bad things will occur. A friend had the errant blade go through the hood, Straight up, well almost. It got only one panel. I was lucky with my two blade when it flew apart, it just ate up the radiator core and grabbed the light wiring.Many of our members have horror stories with both two and four blade fans. The new two blade from the reputable dealers is the best. At road speeds they don't interfere with the air flow and at slow speeds they are adequate for the cars, perhaps not so much for a truck hauling grain out in the field, but not many doing that these days,
 
After my 4 blade fan's rivets let loose and took out my perfectly good radiator, I opted to go with a plastic fan.
 
I have been using a 4 blade fan since I bought the car about 13 years ago. I have not had any problems with it (yet). I have recently heard more and more stories about them losing blades similar to the original 2 blade fans. I don't want to take a chance with that, so I have bought a new repro 2 blade aluminum fan. I just need to install it.
 
The aftermarket 2 blade fans that I have HAD experience with were out of track at the tips, poorly balanced, powder coated inside the tapered hole, and would work loose in a short amount of time. Were they balanced? If so how with blades out of track, poor fit on the shaft, and gobs of powder coat that ran down the length of the blade before curing?
My experience with these has not been good and even though they may now be better, my past experience tells me to leave them on the parts shelf.
Things that spin need frequent and close inspection. I check the oil in my Model A at least once daily before I start the engine. While I'm at it I employ my 2 foot rule. Everything within 2 feet of the dip stick is given an inspection. Ask anyone who has had experience maintaining helicopters. Centrifugal force even on small automotive fans exerts a tremendous load on the blade especially at the root area. I have turned engines over with the fan for al least 55 years without an issue.
It is also hard for me to believe that a fan with absolutely no issues all of a sudden exploded.
Just my opinion backed with experience.
 
I had a late 31 design fan start to crack at the inner junction where the 2 layers come together to 1 layer. I replaced it with an aftermarket balanced cast aluminum and it ran true and gave no problems.
 
One need only see an 80+ year old fan go through the top or the side of a hood once to have a better understanding of metal fatigue. 80 dollars is pretty cheap these days for a cast aluminum 2 bladed fan.
 

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