[mgarblik]

Originally Posted by gto19

Mgarblik

Good info !

If I read your posts correctly you say to move the spring clockwise which would tighten the coil up but when I look at this picture provided in the chevelle link you can see they actually loosened the coil counterclockwise. So what’s the correct way to move it ?

Ha, now I don't know. I may have moved it the wrong way but it seemed to work better? I have to remove the fan, clutch and shroud tomorrow to send it out for powdercoat. I will play with the spring with a hair dryer on the bench and see what the heck I actually did. Sorry for the confusion.

[RocktimusPryme]

Originally Posted by gto19

Mgarblik

Good info !

If I read your posts correctly you say to move the spring clockwise which would tighten the coil up but when I look at this picture provided in the chevelle link you can see they actually loosened the coil counterclockwise. So what’s the correct way to move it ?

That was kinda my question too. The videos I posted both moved it to the left (CC) as well. But they may have been reverse spinning water pumps?

Im still slightly confused. I might take a picture later and draw on it just to clear up the confusion.

I think I might be afflicted by exactly what you guys are talking about. The fan coming fully on too late. My car sits dead on the 180 thermostat when moving, but climbs some when idling. So I would like to give this mod a shot, but Im still not sure where I should put the outter tang of the spring.

Im a visual person lol. Trying to visualize it in my head Im struggling with.

[RocktimusPryme]

Okay lets look at an illustration to try and clear this up.

So Mick this is how you are saying it should go right? Move the spring to tighten it? And let the outer tang just rest against the side like that.

[gto19]

Originally Posted by RocktimusPryme

Okay lets look at an illustration to try and clear this up.

So Mick this is how you are saying it should go right? Move the spring to tighten it? And let the outer tang just rest against the side like that.

No
Go the other way . You wanna loosen the spring . What he was saying is bend the outer tang clockwise and that will force the coil and center pin counterclockwise. On your fan clutch picture bending the tang really won’t do anything since you don’t have a slot that it rests in .

I provided a picture of my original fan clutch without the modification and a pic of a fan clutch with the modification

[gto19]

Actually looking at yours more close up you probably could bend the tang clockwise and leave it in the hole and it would force the coil counterclockwise

[RocktimusPryme]

Originally Posted by gto19

Actually looking at yours more close up you probably could bend the tang clockwise and leave it in the hole and it would force the coil counterclockwise

Is there room to bend the tang. It doesnt seem like there is much room for error with the 2797 pictured.

That said I think I understand now. Bend the tang to the right which would loosen the spring slightly. Bending the tang right is the same as moving it a slot left.

Could it just be moved out of the slot to the left and rest against the circular knob? Even maybe soldered to the side so it would stay put.

[gto19]

I’d have to actually have the 2797 in my hands to figure out what I’d do . I’d try bending the tang and see what happens. Or moving the tang completely out of the circle to left like you said .dont know if I’d sotter it . Would just have to see . Moving it completely out of the circle might be to much of a drastic change though . I think you kinda just have to play with it

[lust4speed]

Originally Posted by RocktimusPryme

Is there room to bend the tang. It doesn't seem like there is much room for error with the 2797 pictured.

That said I think I understand now. Bend the tang to the right which would loosen the spring slightly. Bending the tang right is the same as moving it a slot left.

Could it just be moved out of the slot to the left and rest against the circular knob? Even maybe soldered to the side so it would stay put.

That is correct. Removing the spring from its current position and moving it to the left (say 12:00 to 11:00) is what you want to do. Give that a try and if the fan stays on too much then take my riskier approach and bend the end of the tang. I've heard guys succeed with moving it out of the slot and leaving it loose, but never had an update whether the pin might migrate farther around since it is now free floating.

What can sometimes happen is you move the tang too far and it lets the fan stay on under 180° and your thermostat is a little lazy and keeps temps at 185° -- and the fan will always be on trying to fight the thermostat.

I really didn't want to post this ugly photo but it does show the bent tang that allows the center pin to be slightly more counter-clockwise. In this particular case the slots on the pin were originally in a 9:00/3:00 location and you can see a very slight pitch on the pin now.

I'm also wondering if a slot might not be cut with a Dremel tool about half way between the stock slot and the outside of the casting?

[68 Firebird]

Lust is correct doing this mod helped my cooling tremendously. I probably got a little overzealous with adjustment though. temps were stable at 185-190 and ran that way for 7 years. Also did other upgrades along the way 8" crank pulley, 6.5" waterpump pulley, WP clearance to minimum gap, all filler panels, air dam and AC plates helped as well. The new CC radiator also is no slouch and just wanted to see what result would be or if I needed to go back to a 2797. All I can say is the 2797 served me well and that is what I would use with slight spring mod. Good Luck Gerry

[RocktimusPryme]

Originally Posted by lust4speed

That is correct. Removing the spring from its current position and moving it to the left (say 12:00 to 11:00) is what you want to do. Give that a try and if the fan stays on too much then take my riskier approach and bend the end of the tang. I've heard guys succeed with moving it out of the slot and leaving it loose, but never had an update whether the pin might migrate farther around since it is now free floating.

What can sometimes happen is you move the tang too far and it lets the fan stay on under 180° and your thermostat is a little lazy and keeps temps at 185° -- and the fan will always be on trying to fight the thermostat.

I really didn't want to post this ugly photo but it does show the bent tang that allows the center pin to be slightly more counter-clockwise. In this particular case the slots on the pin were originally in a 9:00/3:00 location and you can see a very slight pitch on the pin now.

I'm also wondering if a slot might not be cut with a Dremel tool about half way between the stock slot and the outside of the casting?

See on that model is does look like you could cut another slot in it. On the one I pictured pulled from Summit it didn't look like there was room. Ill have to go out and look at mine personally and see.

I was thinking about buying the shorter version of the HD clutch (cant remember the number), because my fan is like 90% in the shroud all the way around.

[mgarblik]

I was able to do some bench testing with a hair dryer and can report some findings on the 2747 clutch at least. First, I am convinced after my testing that just laying the tang of the bi-metalic spring against the stop is a bad idea and either the clutch will be in a clutched-up condition almost all the time or at least be inconsistent. As the spring heats up the end of the tang moves counterclockwise and the valve is free to basically do whatever it wants. It can wiggle all the way from fully open to closed at will when hot with the spring not restrained. Bad idea, and the Chevy article is incorrect in saying that's a good idea. Sorry for assuming that information was reliable. I took 5 pictures which will describe how the spring and valve work and the little modification I tried. On the bench it makes sense that it will help. Actual temperatures I won't be able to verify for a few weeks as the shroud is out being powder coated.
picture 1 and 2 are for reference only. In pic 1 you can see the spring unhooked and the valve split line pointing to UC (unclutched). Pic 2 shows the spring heated and the tang has moved counterclockwise further than pic 1. I turned the valve to C, (clutched so you can see the total movement of the valve. It's only about 45 degrees total which makes this adjustment pretty touchy. Pic 3 shows the spring in a Hayden 2747 in the stock location at room temperature. Pic 4 shows the tang in the NEW slot I carefully cut in the clutch with a Dremel cutoff wheel. Go slow and careful. Pic 5 shows the spring in the new tang heated up and the valve split pointed toward C, (clutched) This little mod will open the valve at a lower temperature, just not sure how much yet. We want our old muscle cars with carburetors and this crap gas to run around 180 degrees on a hot day. A clutch that really doesn't fully engage until 200-210 water temp is too hot for best operation and function with a carburetor. I will report back in a few weeks.

[RocktimusPryme]

Thanks. The visuals do help a lot.

I don’t how much clamping force it takes the hold the spring there if you rested it against the side. Would solder work? Super glue? Etc.

Cutting a new slot definitely seems the way to go if there is room to do so

[mgarblik]

Got my shroud and other pieces back from powder coating this afternoon. I will install them and road test soon. Supposed to be back in the low/mid 90's first of the week with high humidity. Should be a good test.

[mgarblik]

Got my shroud and other pieces back from powder coating this afternoon. I will install them and road test soon. Supposed to be back in the low/mid 90's first of the week with high humidity. Should be a good test.

[mgarblik]

Did some real world, anecdotal testing today of my new set-up. Outside temperature 94 degrees. Heat index 99 degrees F. start-up and drive 20 miles to friends house. Mostly country roads, speeds 45-60 MPH. Temp goes right to 175 water temp and I can hear the fan clutch-up. Creeps to just under 180 and begins dropping back to just under 175. Arrive and let car idle in the heat for 1/2 hour. I can hear the fan clutch up but temp does creep to just under 180. Shut engine off. Heat soak takes it to 190. Leave after an hour and start engine, within 30 seconds it's at just under 180. Leave his driveway and within 2 minutes it's at 170 degrees. Stays stable for 20 mile drive to gas station. Heat soaks to 200 while getting gas. Once started, drops back to just under 180 in a few blocks. Let it idle in the heat another 25 minutes and put in garage, temp 185 degrees. Shut off and it heat soaked to 210 degrees F.
Conclusions: Overall, temps cruising are about 10 degrees cooler. Engine has maximum cooling efficiency at 2000-2300 RPM. At that cruising speed, maximum heat is removed quickly. With clutch fan after heat soak heat is removed much faster. At prolonged idle, temp does creep up slightly but does much better staying under 190 no matter what. With direct engine driven 4 blade, it would continue to climb idling and would not level off or drop without road speed. I would call the exercise a success.

[tempest1964]

Mike, this is a great tutorial, what with the visual aids and all. If I didn’t know any better, I’d say you were a teacher in a previous lifetime! Just kidding. Once a teacher, always a teacher. Thanks for the thread, it really cleared it up for me. I’ll add it to the other things I’ve bookmarked for my 421 when I finally get around to building it.

[jschaible]

Mike, thank you so much for this careful research. This is incredibly useful for my situation, and also caused me to join the forum. I feel like I found a gold mine.

I installed a Hayden 2747 clutch in my 69 Catalina 400 yesterday. But after reading your post last night, I took it back out this morning and cut a new slot for the spring tang, as you showed in those pictures. I do not have a temp gauge on this car, but I can confirm that the fan is clutching up at lower temperatures and consistently declutching when it should. It's running noticably cooler across the board (by sound). Today was 85F and sunny, AC on and car loaded with 800lb of passengers and cargo. Kept the heat under control at traffic creep and 75 mph cruise. Thank you again.

[mgarblik]

There are many very smart people on this forum. Carburetors, tuning, engine building, body and paint, you name it. I have over 40 years of experience and learn new things nearly every day on here. This is THE place for Pontiac people.

[grivera]

Thanks for contributing the research Mike! I did the mod on my 2747 Fan clutch yesterday and hope to test this weekend.

[grivera]

Originally Posted by mgarblik

The Hayden tech info recommends the severe duty clutch with fan blades of 2.5" pitch or more. That may be why some people are unhappy with this clutch if they are using a 2" pitch or less fan blade.

How does one measure fan pitch in inches?