5 Blade Fan Help Please ! - NCRS Discussion Boards

5 Blade Fan Help Please !

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  • Rick B.
    Frequent User
    • June 30, 1998
    • 75

    #16
    Re: 5 Blade Fan Help Please !

    Originally posted by Joe Lucia (12484)
    Rick------


    If you have the correct locking style motor mounts, the engine should not be able to rotate more than about 3/8".

    Joe, when I rebuilt the motor I did some internal changes to give it much more torque. Consequently it consistently delivers 575 lbs of torque and just shy of 500 hp all while maintaining stock intake, heads, exhaust manifold, etc.
    Because it is geared relatively low I chose not to go with the OEM style mounts.
    I spent a considerable amount of effort balancing everything so I put in the hard poly-mounts for fear of too much movement and tearing to the rubber mounts. As I am still breaking the motor in I had been doing some "hard pulls" when I let off the pedal just as the transmission shifted ( and possibly just when the stator locked up ) resulting in a hard jolt to the drivetrain. I believe this combination of events was enough to allow for the extra movement and the fan to then contact one of the bolt heads on the upper shroud bracket - which instantly deformed the blade and resulted in further damage on each subsequent revolution. A tough lesson to learn as I had always been leery of the minimal clearance at that junction but had seen no evidence ( until yesterday) of contact and believed all was good.
    I have since looked over everything and can see no evidence of anything else that could have contributed to this but am always open to suggestions as I want to avoid this from ever happening again.

    So Joe, if I were unable to find the correct 5 blade fan and went with the 7 blade #342715, is it correct to assume that GM engineers would have expected one to use a different fan clutch like the #343721 with it since it would likely have been designed differently given the additional contact with more air/surface area than what my original Schwitzer fan clutch would have handled on a non A/C car? Also, is it automatically a given that the 7 blade will be noticeably louder than the 5? What have others reported going to a & blade fan?

    Thx !!

    Comment

    • Joe L.
      Beyond Control Poster
      • January 31, 1988
      • 43195

      #17
      Re: 5 Blade Fan Help Please !

      Originally posted by Rick Bandura (30672)
      Joe, when I rebuilt the motor I did some internal changes to give it much more torque. Consequently it consistently delivers 575 lbs of torque and just shy of 500 hp all while maintaining stock intake, heads, exhaust manifold, etc.
      Because it is geared relatively low I chose not to go with the OEM style mounts.
      I spent a considerable amount of effort balancing everything so I put in the hard poly-mounts for fear of too much movement and tearing to the rubber mounts. As I am still breaking the motor in I had been doing some "hard pulls" when I let off the pedal just as the transmission shifted ( and possibly just when the stator locked up ) resulting in a hard jolt to the drivetrain. I believe this combination of events was enough to allow for the extra movement and the fan to then contact one of the bolt heads on the upper shroud bracket - which instantly deformed the blade and resulted in further damage on each subsequent revolution. A tough lesson to learn as I had always been leery of the minimal clearance at that junction but had seen no evidence ( until yesterday) of contact and believed all was good.
      I have since looked over everything and can see no evidence of anything else that could have contributed to this but am always open to suggestions as I want to avoid this from ever happening again.

      So Joe, if I were unable to find the correct 5 blade fan and went with the 7 blade #342715, is it correct to assume that GM engineers would have expected one to use a different fan clutch like the #343721 with it since it would likely have been designed differently given the additional contact with more air/surface area than what my original Schwitzer fan clutch would have handled on a non A/C car? Also, is it automatically a given that the 7 blade will be noticeably louder than the 5? What have others reported going to a & blade fan?

      Thx !!
      Rick------


      Using the polyurethane engine mounts, I'm surprised the engine would torque-rotate, at all. Personally, though, I don't recommend using poly mounts and would never use them myself.

      The GM #342715 was never used with your original fan clutch, assuming that what you have for a clutch is a GM #3991426. However, I think the 342715 could be used with an original fan clutch without any problems, whatsoever. In fact, for some pre-1971 Corvette applications, GM used a 7 blade fan to replace the original 5 blade fan for SERVICE with no change, at all, as far as the fan clutch goes. As far as noise is concerned, I don't think you'll notice any discernable difference. I once replaced the original 5 blade fan on my 1969 with the 7 blade GM fan and I don't recall any noise increase.

      Now, as far as FUNCTIONALITY is concerned, I would recommend replacing your current fan clutch with a GM #88961768, aka Delco 15-4950. You could do it with either the 3991420 fan blade assembly or, better yet, with the 342715. The predecessor of this clutch is the best performing fan clutch EVER installed on a Corvette and the 88961768 differs from its predecessor in only very minor ways. It does have a completely different configuration than your original fan clutch, though. However, this fan clutch will be LOTS noisier. LOTS. That's because it's moving LOTS more air, especially at idle or low vehicle speeds. Keep this in mind: when you increase the torque and power of an engine, you also increase heat rejection (cooling) needs. I've never known ANY Corvette to have too much cooling capacity. Many are marginal, even at completely stock engine configuration. Some fools or "economically challenged" individuals think they can solve the cooling problems with a thermostat change. Dream on!
      Last edited by Joe L.; October 29, 2017, 02:30 PM.
      In Appreciation of John Hinckley

      Comment

      • Rick B.
        Frequent User
        • June 30, 1998
        • 75

        #18
        Re: 5 Blade Fan Help Please !

        Correct , I have the 3991426 fan clutch currently and would have it inspected/overhauled if necessary to be safe.

        So, I am a little confused since you said there shouldnt be any discernible difference in noise between the 5 blade and 7 blade #342715.
        But you mentioned the better performing clutch (#88961768 or Delco 15-4950) would be significantly louder.
        I had no idea fan clutches generate "much" noise - I always attributed the noise to the fan ( # of blades, pitch, etc) ! Hmmmmm !
        What makes this clutch so noisy in your opinion?
        Thank you Joe

        Rick

        Comment

        • Joe L.
          Beyond Control Poster
          • January 31, 1988
          • 43195

          #19
          Re: 5 Blade Fan Help Please !

          Originally posted by Rick Bandura (30672)
          Correct , I have the 3991426 fan clutch currently and would have it inspected/overhauled if necessary to be safe.

          So, I am a little confused since you said there shouldnt be any discernible difference in noise between the 5 blade and 7 blade #342715.
          But you mentioned the better performing clutch (#88961768 or Delco 15-4950) would be significantly louder.
          I had no idea fan clutches generate "much" noise - I always attributed the noise to the fan ( # of blades, pitch, etc) ! Hmmmmm !
          What makes this clutch so noisy in your opinion?
          Thank you Joe

          Rick
          Rick------



          Yes, it's the fan blade assembly that actually makes the noise. The fan clutch, itself, makes no noise. However, as it keeps the fan blade assembly more "locked up", especially at lower vehicle speeds, it's a lot noisier. But, the bottom line is the noise is the result of the fan pulling more air. In a vacuum, a fan would not make any noise, no matter how many blades or blade configuration.
          In Appreciation of John Hinckley

          Comment

          • Rick B.
            Frequent User
            • June 30, 1998
            • 75

            #20
            Re: 5 Blade Fan Help Please !

            Thanks for clarifying Joe ! All good info and much appreciated.
            I will continue my search for a #3991420 tomorrow but failing that I will go with the #342715 and even try the 88961768 - if it makes too much noise I could go back to using my 3991426 fan clutch ( assuming it checks out okay ).

            Sincerely, Rick

            Comment

            • Patrick H.
              Beyond Control Poster
              • November 30, 1989
              • 11613

              #21
              Re: 5 Blade Fan Help Please !

              I have used the 88961768 on a couple of cars, and don't find the noise excessive. One of them drove into my place yesterday, and I noted how smooth and quiet the car was overall.
              Vice-Chairman (West), Michigan Chapter NCRS
              71 "deer modified" coupe
              72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
              2008 coupe
              Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

              Comment

              • Rick B.
                Frequent User
                • June 30, 1998
                • 75

                #22
                Re: 5 Blade Fan Help Please !

                Thank you Patrick, that is good news.
                Rick

                Comment

                • Jaime G.
                  Very Frequent User
                  • March 31, 1988
                  • 480

                  #23
                  Re: 5 Blade Fan Help Please !

                  Originally posted by Bob Winters (1653)
                  Rick, Call David Sokolowski (310)329-5334 I was told that he has a lot of parts for all years.He has a lot of ads in the Driveline.

                  Bob
                  Ditto, David should be able to help you.

                  Comment

                  • Rick B.
                    Frequent User
                    • June 30, 1998
                    • 75

                    #24
                    Re: 5 Blade Fan Help Please !

                    Thanks guys, I had left him a message and I am sure he will get back to me.

                    Rick

                    Comment

                    • Bob W.
                      Very Frequent User
                      • November 30, 1977
                      • 802

                      #25
                      Re: 5 Blade Fan Help Please !

                      Rick He will call you it may take a day or two but he will call.

                      Bob

                      Comment

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