[Z Code 400]

Some folks on here are tuning the bi-metal spring on the thermal clutches so they apply later. I have a big, severe-duty clutch and 7 blade fan laying on the shelf that I took off my 1975 Formula. It pulls way too much air when it applies, enough to drop the engine 150 rpm @ 2500!!!!!

The 7 blade Lincoln flex fan works great and is super quiet. At 2500 rpm, I let the alternator adjustment flop all the way down until it threw the drive belt off the pulley and the fan stopped. I couldn't detect a noticeable increase in engine rpm on my tach/dwell meter.

Not very scientific, but much less noise and drag on the engine. The thing about the flex fan is it delivers constant airflow and keeps the temperatures very steady. With the clutch, the temperatures are always fluctuating up and down. My car would run 210°F at night (50°F outside) with a fan clutch!!!!!

The photos below show each fan and then the temperature guage on a +100°F day here in Central California. Even at 130 mph, the flex fan does its job better than the clutch.

Ben Arnold, who competed in the 1969 Daytona 500, recently told me those stock cars would run hot at 170+mph without a fan!!!!!!

[AdamIsAdam]

Old thread. Same questions. So, what is the P/N or other method of finding the right Lincoln 7 blade flex fan? How big is it diameter?

[AG]

I had a Hayden severe duty new clutch and factory 7 blade fan and temps would creep up to 210°F on a 90°+ day in traffic using a 160°F thermostat. Changed to a 7 balde Flex-a-lite flex fan and now my temps will not get to 180°F on a 90°+ day no matter what kind of driving.

[AdamIsAdam]

Originally Posted by AG

I had a Hayden severe duty new clutch and factory 7 blade fan and temps would creep up to 210°F on a 90°+ day in traffic using a 160°F thermostat. Changed to a 7 balde Flex-a-lite flex fan and now my temps will not get to 180°F on a 90°+ day no matter what kind of driving.

It's amazing how different people have different results with what seems like the same parts. I guess it's engine components and the actual car (ie, radiator size) that make the difference.

Anyway, I'm up for trying anything. What size flex fan did you use?

How about this one:
http://www.summitracing.com/parts/flx-1818/overview/

[AG]

That's the one, just measure and see if an 18" or 19" fits and make sure it's away from the radiator. I'll measure how far my fan is away from the radiator and its position relative to the shroud tonight. It's in a '72 LeMans vert with a 9:1 CR 455 with a stock radiator for a 350 2bbl. I had the same results in my '65 LeMans and a factory 5 blade flex was a big improvement on my brother's LeMans over a stock 4 blade fixed fan.

[AdamIsAdam]

ok, thanks. Pics would be helpful too!

[lust4speed]

Originally Posted by AG

I had a Hayden severe duty new clutch and factory 7 blade fan and temps would creep up to 210°F on a 90°+ day in traffic using a 160°F thermostat. Changed to a 7 balde Flex-a-lite flex fan and now my temps will not get to 180°F on a 90°+ day no matter what kind of driving.

That's because Hayden in its infinite wisdom, set the thermostatic switch to turn on at that temp. Let the car idle in your driveway with a stock 2797 fan, and you can hear the fan lock up when the coolant temp hits around 210°. Their website has changed over the years and initially said their fans turned on at 180 to 190 degrees air temp, and that figures out 210° coolant temperature with the heat absorbed and being drawn out of the radiator. They now state a lower number, and maybe they did change it, or maybe they just changed their advertising. Anyway, that's why we alter the spring to engage the fan at a little lower temperature.

Most newer cars and trucks were designed to run hotter, and that was the market Hayden was aiming for. A few years ago I sent a letter to Hayden explaining what we needed and requested they produce a fan specifically for our cars, and suggested that they could name it the 2797M, with the M designation for muscle cars. Not surprisingly, I never heard back from them.

By the way, on a 100+ day with my A/C on full, my car will stay at 165° thermostat temp cruising down the freeway. I also don't turn the air off stuck in bumper to bumper traffic, and it still stays under 190° after a half hour of making a half mile progress. That's with the altered SD clutch fan, 19.5 GM fan, and 6" water pump pulley. Only piece of heresy is the stamped steel impeller doing its thing. That got put on after three failures in a row with new Cardone pumps that had the cast impeller (this was about a dozen years ago, and I haven't heard of any failures since - just a bad production batch). Picked up a stamped steel one from NAPA, and found out that it ran as cool in all driving. That was running the cast one day and stamped steel the next, so pretty close to a back-to-back trial. My blue car from the Fremont plant came with the stamped impeller, and I would think that Pontiac would have insured that there was no loss in cooling before making the switch.

[AdamIsAdam]

Originally Posted by lust4speed

That's because Hayden in its infinite wisdom, set the thermostatic switch to turn on at that temp. Let the car idle in your driveway with a stock 2797 fan, and you can hear the fan lock up when the coolant temp hits around 210°. Their website has changed over the years and initially said their fans turned on at 180 to 190 degrees air temp, and that figures out 210° with the heat absorbed and being drawn out of the radiator. They now state a lower number, and maybe they did change it, or maybe they just changed their advertising. Anyway, that's why we alter the spring to engage the fan at a little lower temperature.

Most newer cars and trucks were designed to run hotter, and that was the market Hayden was aiming for. A few years ago I sent a letter to Hayden explaining what we needed and requested they produce a fan specifically for our cars, and suggested that they could name it the 2797M, with the M designation for muscle cars. Not surprisingly, I never heard back from them.

Where is that mod on how to alter the spring? I can't seem to find it.

[tinindian68]

http://midamericachevelles.com/tech/...tch_adjust.pdf


Sent from my iPhone using Tapatalk

[lust4speed]

Only thing I don't like in the article is they are moving the coil spring way too far and it will be fully locked up all the time. Another discrepancy in the article is the valve can be rotated in either direction, so you can't rely on it being closed to figure out which way to adjust things. Here's a paragraph I posted a few years ago with a couple changes to clean it up a little:

My disclaimer is “results may vary, and try this at your own risk”. I took a new severe duty Hayden clutch fan and re-indexed the valve on the front of the clutch. This fan has the coil thermal spring permanently mounted to the center pin and the outside spring tip dropped into a cast slot where the spring can be lifted out.

The pin controls the fluid coupling. As the pin is rotated counter-clockwise, the fan engages more. Best way to verify this is to take a hair dryer and apply heat to the coil while the clutch is sitting on the workbench and observe the motion of the center pin as the heat is applied. The object is to have the clutch believe the spring is seeing more heat than it actually is, and the spring needs to be bent to slightly move the center pin in a counter-clockwise direction. Very little adjustment needs to be done and it is easy to over-do the bend. The danger is that the spring could snap off and the fan clutch would be scrap. The actual change needed is to bend the end tang about 5°. Another way to look at it is to make the bend thinking of the hour hand on a clock and move the tip of the tang from 12:00 to about 1:00. It doesn't take much bending, and it's best to start out with very small changes.

Moving the tip of the tang clockwise results in the main spring body moving counter-clockwise which is where it needs to be to engage earlier. While Hayden advertises that the fan engages at 185° air temperature, every fan I've seen waits until about 210° water temp to ramp up. When I got my A/C working the temps wanted to stay right at where the fan clicked in, so I cheated and made the fan come in sooner. My initial attempts were always too much, so try to just barely bend the tang.

I've modified four fan clutches now, and have been happy with the results. Also, I am still running the 8-bolt water pump on my engines. I find that with adding JB weld or Devcon to get the shape of the pump cavity back to new condition, that I haven't really found any cooling difference from the 11-bolt setup.

Think we've modified 9 fan clutches now and everyone seems happy with the results. The only difficult part is each time you make a change to the spring, everything has to be bolted back up and a test run has to be made. I ended up being about 5 degrees off from where I wanted to be, but didn't have the willpower to try another time. Moving the spring tip is not an exact science and its easy to end up on either side of your target zone.

[AG]

Adam,

Here is a pic of my fan in the '72 LeMans. The front of the fan is about 4" away from the radiator and the engine side of the fan is parallel with the shroud.

[AdamIsAdam]

Attachment 410308

Originally Posted by lust4speed

Only thing I don't like in the article is they are moving the coil spring way too far and it will be fully locked up all the time. Another discrepancy in the article is the valve can be rotated in either direction, so you can't rely on it being closed to figure out which way to adjust things. Here's a paragraph I posted a few years ago with a couple changes to clean it up a little:

"My disclaimer is “results may vary, and try this at your own risk”. I took a new severe duty Hayden clutch fan and re-indexed the valve on the front of the clutch. This fan has the coil thermal spring permanently mounted to the center pin and the outside spring tip dropped into a cast slot where the spring can be lifted out.

The pin controls the fluid coupling. As the pin is rotated counter-clockwise, the fan engages more. Best way to verify this is to take a hair dryer and apply heat to the coil while the clutch is sitting on the workbench and observe the motion of the center pin as the heat is applied. The object is to have the clutch believe the spring is seeing more heat than it actually is, and the spring needs to be bent to slightly move the center pin in a counter-clockwise direction. Very little adjustment needs to be done and it is easy to over-do the bend. The danger is that the spring could snap off and the fan clutch would be scrap. The actual change needed is to bend the end tang about 5°. Another way to look at it is to make the bend thinking of the hour hand on a clock and move the tip of the tang from 12:00 to about 1:00. It doesn't take much bending, and it's best to start out with very small changes.

Moving the tip of the tang clockwise results in the main spring body moving counter-clockwise which is where it needs to be to engage earlier. While Hayden advertises that the fan engages at 185° air temperature, every fan I've seen waits until about 210° water temp to ramp up. When I got my A/C working the temps wanted to stay right at where the fan clicked in, so I cheated and made the fan come in sooner. My initial attempts were always too much, so try to just barely bend the tang."

Think we've modified 9 fan clutches now and everyone seems happy with the results. The only difficult part is each time you make a change to the spring, everything has to be bolted back up and a test run has to be made. I ended up being about 5 degrees off from where I wanted to be, but didn't have the willpower to try another time. Moving the spring tip is not an exact science and its easy to end up on either side of your target zone.

Mick,
EDIT: I think I follow you now. So you are opening up the bend at the outside end of the spring from 90* to 95*. It is then put back into the "C" and we have just effectively loosened the spring, making the center turn counter-clockwise. Right?

As an FYI, this doc on their site backs up what you said, in that the clutch operates at about 30* lower than the gauge temps will show.



Here are two CRUDE sketches of what I was trying to write:

[lust4speed]

Your drawing indicates the end of the spring being bent the correct way. Hayden changes their fan specs without letting us know, and it might be worthwhile to install the fan clutch as purchased and just see where the running temp ends up. Plus I would bet that there might be a pretty wide production tolerance and you might end up with one right out of the box that is close to acceptable. The amount we bend the spring is probably around two or three thicknesses of the spring itself, or possibly not much more than .060". That's why I found the article strange that they were moving the tip of the spring 180° to the other side.

Since you don't want to be bending the spring any more than necessary, it's also not a bad idea to note the position of the center pin slot, and use that as a guide to see your actual changes.

[AdamIsAdam]

How do you actually work on the spring? Do you lift it out? What do you use to bend it?

Does the center valve free spin that I need to be careful of?

[lust4speed]

The spring is captured by its being crimped to the center pin, and the outside tang should move out of the aluminum cavity just far enough to be able to work on it. Basically you will just be using the play in the coils to gain enough height to get it clear and grab the end of the spring.

I use two long nose pliers and just tweak the end a little bit. The spring is softer than what I would have thought. The center pin will turn quite a distance either way, but I never moved it over maybe 15 or so degrees while bending the end. I was always afraid of screwing something up inside.

[AdamIsAdam]

Excellent. Just what I needed. I ordered the clutch. Just need to find the right fan now. I have a non AC car and non OEM radiator so I'm not sure if a 19" fan will work, I may need 18". Then the question is what pitch to buy. Open to suggestions.

[AdamIsAdam]

Am i relegated to this fan or can I make a 19" fan fit? Remember, I have a non-AC car, but have a non-OEM radiator with a 21x18" core. I'm actually not sure a 19" fan will clear my lower radiator hose.

[lust4speed]

There's another thread where we were talking about using the 19.5" fan with the short 15.5" stock radiator. Basically, the fan clears okay, and the big shroud works also after some hacking away at the bottom around the outlet. We center the fan up and mark the shroud where the outlet cut has to be raised up on the shroud. Only converted two so far, and both were successful. Luckily the chopped up bottom doesn't really show up from the top because its not pretty. The bottom edge of the shroud ended up at the bottom of the lower tank. There was a point on the first one where we were wondering whether we had just destroyed a brand new shroud. The motivation for both friends was they were starting fresh and were going to buy everything anyway - the fan, clutch, pulleys, and the shroud. Since supersizing things really didn't cost much more, it was an easy decision to make for them.

I didn't go that far on my blue HO car. I swapped over to the 2797 clutch and a smaller 6" pulley, but kept the original smaller diameter HO fan and its shroud. WAG is maybe 10-15% less cooling capacity. While the Cruiser will not go above the 165° (160 thermostat that's always opened five degrees higher) without the A/C on no matter what the terrain or driving conditions, the blue car will move from 160 to 180 on grades on a hot day. My next step would have been the large fan and shroud, but its passable the way it is.

[AdamIsAdam]

Hmm. So, given everything you know about my setup and my issues with cooling, do you think it's worth the effort of hacking up a big shroud?

I have to first see if the 19" fan clears my lower radiator hose though.

[lust4speed]

That's a tough call. The larger system should be overkill, but we do things that make overkill a good idea - larger engine displacement, lower gearing, and generally just driving harder than Pontiac intended back then.

I was looking on Ames, and while my original '67 H.O. fan measures 18", the fan they are selling now is 17.5" according to their catalog. This would again decrease airflow, and also allow more room between the fan and shroud. Get too much clearance and you just as well not have a shroud - sort of like the water pump clearance.

Pontiac didn't bother to include a shroud with the HO package which I always thought strange. I factory ordered the car and only had it a few weeks when I got stuck in traffic and watched the temp gauge climb past 215°. Scared the hell out of me and I stopped by the dealer and asked what was up, and they recommended I buy a shroud. The shroud was under $12 and they had to order it. Once installed, the car never got over 200°. Think the car came with a 190° thermostat, so a 10° increase while in traffic or climbing grades wasn't bad. The HO package also had a 7" bottom pulley and an 8" top pulley which was good for drag racing, but not for cooling. Right now those pulleys are on the shelf, and an 8" bottom and 6" top are on the engine.

If you have the smaller fan assembly, I'd run it and see how it works out. You can always throw more money at it later on.