Can you use a universal flex fan with the stock fan clutch on a 67 SB?

Thanks

 

I will say no, since clutch fans use a larger bolt circle for attachment of the fan to the clutch (and then the clutch mounts to the water pump flange via separate bolts), and clutch fans are rigid by design.

Whereas flex fans I have used (both aftermarket and factory), use long bolts (via an extension) that bolt directly to the water pump flange.

The flex fans and extensions should be available at most larger parts stores, or on line at Summits or Jegs. You just need the water pump bolt circle diameter, the length of the extension, the dia. of the fan, and determine how many blades (how much airflow / noise you want / can stand).

Note that the better (and all OEM fans I have seen) flex fans use an odd number of blades to prevent drumming or other "odd" strong noise at certain RPM's.

Hope this answers your questions,
Plasticman

 

Thanks for the answer. Another question... I'm replacing the motor. I do have the cutch and old fan cleaned up, however I was thinking about just replacing both with a flex fan. The seem lighter and look a lot better. Is there any reason why I should stay with the orginal fan and clutch?

Thanks

 

Yes, Noise.

 

Flex fans are a favorite of mine for a variety of reasons. Both clutch fans and flex fans have advanages and disadvantages. I will try to remember them all (see below):

Flex fan:

Advantages:

1. As you noted, lighter (less wgt. on water pump bearing, but note that most water pump bearing side loading is from the driving belt).

2. Work at low RPM where most heat load overheating occurs (slow traffic, parades, etc.), and flatten out (less load) at higher RPM, where vehicle speed forces most air flow through the radiator anyway.

3. Less complicated and more reliable (debatable due to some crappy designs of both on the market, but should be fact).

Disadvantages:

1. Always "on" at low speed, even when temperatures do not need it.

2. More noise (but "odd" number of blades are quieter, and more blades are always better - for both airflow and noise control, but as air flow goes up, so does noise). In other words, a 6 blade with a steep pitch, may flow a lot of air, but a 7 blade with slightly less pitch can flow the same or more air, with less noise overall, and not drumming like an even blade fan can do.

3. Have been known to fling a blade (have also seen a clutch fan do this, as well as the little fan on a 10SI GM alternator, so "crap does happen!").

Clutch fan (only talking about OEM thermostatic controlled versions - the non thermo units are just cheapy replacements):

Advantages:

1. Only pass air when needed (when hot, fluid couples fan into motion).

2. Quieter!

Disadvantages:

1. Wear of internal bearing will cause vibration (which can be difficult to find!).

2. More costly to repair or rebuild.

3. Heavier.

Note that GM (as well as all the US auto makers) have used both types in the past. Have seen a "huge" flex fan that GM offered as part of a "fix" for 70 era big block Vettes that constantly overheated in slow traffic. I put that fan on my 70 Vette (SBC 350/350) that never overheated again, including daily tollway trips (long tollway booth lines) on hot Chicago days. Note that the original clutch fan was the cause of the original owner trading the Vette in (dealer could not find the cause of a significant vibration above 3K RPM - under warranty, after replacing just about every rotating part in the Vette!).

Don't know if I covered them all, but good luck.
Plasticman

 

And Safety ; flex fans are notorious for throwing blades. Also, the stock fan and clutch (with the correct shroud) will move a LOT more air than a flex fan, and will disengage over 3500 rpm. Trying to re-engineer the cooling system out of a Summit catalog generally results in failure.