Old style red fan (mechanical coupling) question

[Luis A.]

The older style red fan that worked with the mechanical 'clutch' coupling has two different part numbers and I'm trying to figure out the difference.

PN 11521252660 is described as 400 mm in diameter and according to the parts books, used up to 73. After '73, still with the mechanical coupling, PN 11521259664, also described as 400 mm in diameter and appearing as the same item on the diagrams, was available. Fan 664 appears for sale online, but in photographs look exactly the same to me.

Does anyone have a 664 fan to compare measurements and characteristics to the 660 that I have? Or know the differences? My fan has the number " 252 660" molded on the back.

Photo of a 664 fan below.

 

[Mot27cars]

The older style red fan that worked with the mechanical 'clutch' coupling has two different part numbers and I'm trying to figure out the difference.

PN 11521252660 is described as 400 mm in diameter and according to the parts books, used up to 73. After '73, still with the mechanical coupling, PN 11521259664, also described as 400 mm in diameter and appearing as the same item on the diagrams, was available. Fan 664 appears for sale online, but in photographs look exactly the same to me.

Does anyone have a 664 fan to compare measurements and characteristics to the 660 that I have? Or know the differences? My fan has the number " 252 660" molded on the back.

Photo of a 664 fan below.

View attachment 91113

I have mine from a 72 Bavaria in the shop. I can look at it tomorrow to confirm part number

 

[Luis A.]

It should be a 660 but if it happens to be a 664, see if you can take a measurement of one the blades and some pics. The diameter is awkward to measure since none of the blades are diametrically opposed to one another.

 

[HB Chris]

Luis, our 2800 had a red fan, 7 3/4” from center post to tip of each blade or about 39.5cm diameter. If it is like the 2002, they had a larger ‘tropical’ fan for improved cooling. I can’t find a number on our fan.

 

[Fredomatic]

Luis, I though I might have the 664 as I have two 5 blade reds but alas they’re both 660’s. Interestingly I found during my recent water pump and fan replacement that the two fan clutch housings are ever so slightly different. See photos. Can you see how one is slightly smaller than the other? This allowed one fan to spin when bolted and the other to seize. Both with 25mm bolts. All said and done, the clutch spins when cold and only engages with some force when hot. Frustrating. Good luck with your query.

 

[Fredomatic]

and now for the photos...

 

[Luis A.]

Thanks for the replies. Chris if yours doesn't have a molded PN on the back, I wonder if it is a 664 since my 660 has the molded number.

Maybe the 664 has a more aggressive pitch on the blades...?

The parts book calls them both out as 400 mm and specifically, the 664 for all 3.0 models. If you are well-versed in BMW parts book hieroglyphics, tell me if I am interpreting this correctly, that all Euro 3.0 models received 660 up to 73 and all 3.0 USA models up to 74 and after that, 664. Also the 1 groove pulley (356) goes to 1 groove (234) (which I don't get) but a 2 groove pulley (235) remains available.

Fred: I see the assemblies look different but the effective installed height remains the same since the bolt mounting points are at the same height. The clutch pack does appear to be a bit different in eight but the service book cautions that clutch carrier and the temperature expanding element are a matched set and to be replaced as a set. You write: "the clutch spins when cold and only engages with some force when hot ", but that is how it IS supposed to work... Maybe I'm not understating correctly; can you clarify?

I am looking at all this because I'm going back to the friction clutch. All 4 viscous clutches I have experienced on 2 different cars exhibit a high degree of coupling when the car is cold and not in need of cooling so the noise level is higher than it needs to be. The friction clutch worked excellently for me, it is simple and reliable, and the friction shoes suffered very little wear on my car. The fan truly freewheels on a ball bearing (replaceable by the way) turns on and off almost like an electric fan only working when you need it. In addition, I have the AC electric fan wired to the lower radiator sensor so it acts as a backup or supplemental cooling when needed, which I have never been even close to.

 

[Fredomatic]

Luis that’s good to hear your take on the old 5 blade fan as a lot of people disregard it. In my case I switched a fan that was locked up with 30mm bolts by the previous owner. It was super noisy and probably added stress to the water pump. I was under the impression that the clutch should nearly lock up with friction when the engine is hot. Maybe that’s incorrect? My fan engages moderately without significant force and can be stopped and reversed by hand. It’s quiet which is nice. It hasn’t overheated but I have seen the temp gauge jump up at a long stop light. I’ll shoot a video later to give you a visual.

 

[HB Chris]

Luis, You are correct, the fan changed at the start of US MY 74 production which is a Euro Modell 73. The later 74s received a viscous clutch at 4310304 and 4335367 with a different fan. The parts book shows retroactive interchangeability so it’s hard to tell where it applied except in the case by MY. Same changeover for e3 as well.

My 73 has a two row pulley which drives the Alt and PS. Some PS pumps were driven direct from the crank though.

 

[Luis A.]

I was under the impression that the clutch should nearly lock up with friction when the engine is hot. Maybe that’s incorrect? My fan engages moderately without significant force and can be stopped and reversed by hand.

I didn't understand this from your previous post. Yes, the fan locks up tight enough to spin the fan without slip and when cold it's a total freewheel; you can easily hold it still. I've not tried to overcome when engaged it to see how strong it is but it pulls air with force and in my hands, not mounted, when heated, locks up strongly enough that I can't turn it.

Since each expansion unit (the part with the little fan ) is matched to the clutch make sure you haven't mixed up. And also that the small cylinder (photo below) is in place. I believe that is the element that gets trimmed to each assembly to make sure the engagement takes place firmly at the prescribed temperature (55C/131F).

See below for the cylinder that should not be missing. Since you have two units, you can maybe confirm my hunch that the cylinder is of different length for each unit.

 

[HB Chris]

Mine is a 660 but that little pin is missing or it is retracted?

 

[Stevehose]

Locking the fan is actually recommended in the blue books in case of (frequent) failure of the friction clutch so it won’t do any harm. This friction clutch is probably the reason so many heads cracked back in the day. I wouldn’t trust my engine to this flawed device, but I respect your goal to make it original. The 5 blade fan also blows a turbulent air stream, it wreaked havoc on #1 carb of my triple webers, took me months to figure it out.

 

[Luis A.]

Chris the little cylinder is there or you would see an empty cavity. It’s just retracted. Heat it up from the other side and you’ll see it poke up.

Steve I’m actually not going after originality but improved functionality. There is no doubt the viscous clutch is lower maintenance (none!) than this one, especially for a daily driver in the 70s. But I don’t know that it was responsible for heads cracking more than the flawed cooling passages were. I ran the car (a lot) with that fan/clutch for three years without any cooling system maintenance and has zero issues.

With a well-maintained cooling system, and not being a daily driver plus, with the electric fan and sensor in place I feel pretty good about it.

 

[Fredomatic]

I didn't understand this from your previous post. Yes, the fan locks up tight enough to spin the fan without slip and when cold it's a total freewheel; you can easily hold it still. I've not tried to overcome when engaged it to see how strong it is but it pulls air with force and in my hands, not mounted, when heated, locks up strongly enough that I can't turn it.

Since each expansion unit (the part with the little fan ) is matched to the clutch make sure you haven't mixed up. And also that the small cylinder (photo below) is in place. I believe that is the element that gets trimmed to each assembly to make sure the engagement takes place firmly at the prescribed temperature (55C/131F).

See below for the cylinder that should not be missing. Since you have two units, you can maybe confirm my hunch that the cylinder is of different length for each unit.

View attachment 91138View attachment 91139

Yes the center cylinders are different heights on each fan. I thought this might be due to wear and without a good connection it might not be heating up enough to seize the clutch. Hmm? Anyhow I would like to move to the 9 blade system. Good luck with your question. I’m sure you will get to an answer soon.

 

[Luis A.]

Fred send me a PM if you’d like to sell those two clutches.

I’m gonna corner the market on that Flawed Device

 

[Fredomatic]

LOL. You got it! I’ll contact you once I have a working system. Yours worked correctly, so it’s probably not a flawed system. Mine is probably worn out or not set up properly.

 

[sfdon]

I thought I cornered it!
Let me know if you need something Luis

 

[Stevehose]

I always knew Don had a lot of flaws!

 

[sfdon]

Different shapes
3 different part numbers

 

[Luis A.]

Wow, that's interesting Don. The fan on the right is the one I have. The one on the left is what the one in the parts book diagram looks like.

Are the blades wider for the one on the left? Are they also 200mm from center to tip, or 400 mm in diameter? Is that a "99" date code? So some cars had still a 5 blade fan in the age of viscous couplings?