[lust4speed]

There was a nice 7 blade 19.5" flex fan offered but the new ones are a little smaller at 19". Maybe I just didn't look hard enough, but think that's the current situation. Both the 19.5" flex fan and the stock 19.5" A/C fan with the 2797 were dead equal in max cooling with my testing, but I found the constant noise of the flex fan a little too much.

While it is a little risky, I bend the end tang of the spring to alter the engagement of the 2797 clutch. I usually see temps higher than what Hayden claims and my new clutches are engaging between 210° and 215°. You go too far on bending the tang and the fan is on all the time, and you make too many adjustments to the tang and the fan will be a paperweight when the end breaks off. It would have saved some time and aggravation if I had been aware of the Chevy magazine article, but I re-invented the wheel on this. The current clutches I've seen have the tang end in an aluminum slot so the magazine way isn't available. I wrote a letter to Hayden years ago suggesting that they could make a fortune by offering a muscle car fan with an earlier engagement temperature, but didn't get any acknowledgement back from them. Here's a copy of my first writeup on PY:

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 goal 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 minute hand on a clock and move the tip of the tang from 12:00 to about 12:05. 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 175 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.