Old 07-16-2022, 04:23 PM
mgarblik mgarblik is offline
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I measured the pitch of my blade by laying it flat on a table and using a carpenter square to measure the distance from the table to the trailing edge of the blade. (greatest distance from table to blade)

Old 07-16-2022, 04:56 PM
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lust4speed lust4speed is offline
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I still think the tech was wrong. Pitch is a measurement that involves two planes. Your roof of your house might have a 4 in 12 pitch meaning the roof height changes 4" for every 12" of horizontal length. A 2-1/2" pitch mentioned by itself means nothing since there is no ratio, and I suspect the tech was probably just referring to the total drop of the blade regardless of the length. Really what matters on how well the fan clutch works is the combined resistance of all the factors of the fan blade -- diameter, depth, width of individual blades, and finally the shape of the blades with some being a simple flat surface and others having a considerable curve to them.

Many of us have proven the GM 19-1/2" stock AC fan blade works great with the severe duty fan clutch, and I'm thinking the last one of those I measured had 2-1/4" of total height from front to back. We are limited by the radiator to the front and the power steering pump towards the rear on how deep of fan we can run.

Mick Batson
1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress.
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Old 07-17-2022, 09:01 AM
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tempest1964 tempest1964 is offline
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I will just throw this out there because I have a Machinist background. Pitch is also used to measure threads. It is the linear distance from the peak of one thread to the next. Or the distance the thread travels in 1 revolution-same thing. Since the fan moves the same as a bolt would, rotary-wise, the distance the air would travel on the fan in one revolution would be the distance from the leading edge to the trailing edge. Maybe this is why the tech said what he did? Of course with fluid dynamics and greater speed the fluid (air) would increase its speed and linear distance traveled. But static distance in one revolution would give a common comparison measurement.

Old 07-18-2022, 08:38 PM
70GS455 70GS455 is offline
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Join Date: Oct 2002
Posts: 723

Pitch is the term obtained from a propeller, either boat or plane. It is the theoretical amount the prop will move the vehicle when it turns one full revolution. It is measured by measuring the thickness of the blades. So lay the fan on a table and measure the heigth of the blades

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Old 08-01-2022, 09:09 AM
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grivera grivera is offline
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Location: Just south of Baltimore
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Thanks all - I have a 19.5" fan with curved blades.

Will Rivera

'69 Firebird 400/461, 290+ E D-Ports, HR 230/236, 4l80E, 8.5 Rear, 3.55 gears
'64 LeMans 400/461, #16 Heads, HR 230/236, TKO600, 9inch Rear, 3.89 gears
'69 LeMans Vert, 350, #47 heads: Non-running project
Old 08-22-2022, 11:55 AM
michaelfind michaelfind is offline
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Join Date: Aug 2019
Location: Central Texas
Posts: 28

Originally Posted by RocktimusPryme View Post
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.
I realize this is an old question from an old thread and y'all already figured out that the adjustment needs to go counter clockwise. I have been experimenting with my clutch and I think I found what works best for my set up.

I tried moving the tang to the left of the circle but that resulted in the clutch not resetting when cool and basically staying engaged all the time.
I tried to bend a slight tip of the end to stay in the slot but there is not enough material there to make that work.
Also, Super glue did not hold.

I ultimately straightened the end of the spring so that it is held (barely but enough) in the bottom of the original slot but also pushes the coil spring CCW to give me a much cooler temp at idle. I hope this is helpful for others.
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