425 nailhead fan

[ljp602]

So, I am new to the group and just got my 64 riv. It had a slow radiator leak so I thought I best change out the radiator. I am into the job now and find something odd. The fan on the engine is not symmetrical. There are 5 blades on the fan but they are not  close to evenly spaced. Anyone notice this before and anyone know why this is. I guess it is possible that it is balance around the center axis but likely not. Unfortunately I did not see what the orientation was when I took it off. Does it make a difference? Any input would be appreciated.

[jrbartlett]

It is balanced. Most likely the blade spacing is meant to reduce noise. Perhaps someone more in the know will weigh in.

[RivNut]

Air conditioned cars have the non-symetrical 5 blade fans.  No need to be concerned about orientation.   The fan should be mounted on a thermal clutch which, when not engaged, will freewheel.  Make sure that your thermal clutch is operating properly.  You should be able to turn the fan blade without turning the engine. When the temperature in the radiator reaches a certain temperature,  the thermal clutch will engage and the fan will no longer freewheel.

[Seafoam65]

                 As jrbartlett surmised, the purpose of the unevenly spaced blades is to cut down on fan noise. It has to

do with cancelling out sound waves that are created by even phasing of the blades.

[RIVNIK]

hey ED!   How can you tell if the clutch is engaging properly?

[RivNut]

When the weather is hot enough to engage the fan, you'll hear a distinct "roar" come from it.  That's the only way I know to tell.  I have no knowledge of a bench test for it.

[KongaMan]

Run the engine until it's good and hot (i.e. drive it around).  Shut off the engine, then see if you can spin the fan by hand.  If you can, your clutch is shot.

 

Or drape a towel across the grill.  Gun the engine and see if the towel gets sucked into the grill.  If it does, the clutch is engaged.

[RivNut]

The fan when not engaged is still turning and creating some draft.  You'll most likely never hear the clutch engage unless you have some other problems in your cooling system - bad thermostat, corroded passages, clogged radiator, bad water pump, bent fins on the radiator AND/OR a/c condenser, or a missing shroud. When I was using my 63 as my daily driver, I would only hear the fan clutch engage in July and August when I was running the a/c and stuck in traffic on the highway.  

 

[ljp602]

Thanks all for the input. It is great to have all this knowledge on hand. I am wondering if this idea of the unequal spacing of the fan blades was common with other manufacturers in the day.  I don't remember seeing this before my riv.