Hot Rods Fan Noise On The 34 Driving Me Up The Wall

I started getting an inter-mitten sound on the 34 which sounds like the mechanical steel solid fan is hitting something. I hear a twing, the sound you make when you flick a fan blade, every once in a while but it seems to be more often recently. I took the belts off and ran it and there was no noise so I know it's the fan. I tried spinning the fan by hand but it didn't make any noise. I put the belts back on ran it and it made the noise again. I've look and listened and don't see anyplace where it could be hitting. There are no shiny marks on the fan blade edges that would indicate it grazing something. Anybody have any ideas? I can't figure it out and I'm no mechanic by any means.

 

I would pull the fan blade off and inspect it very closely. It might have a crack in a blade or a rivet coming loose. You wouldn't want it to come apart at speed, as it will likely do alot of damage to surrounding parts (rad, hood etc)

 

If your fan has aluminum blades it could very well be starting to come apart, I would agree with the previous post take it off and inspect it closely. HRP

 

Check your motor mounts also.

 

Could be maybe cracked in the center around the holes maybe. Take the waterpump pulley off and inspect the center of the pulley. It could be cracked in the center also and makes that kind of noise.

 

I know you said mechanical fan, is it a clutch fan or solid?

 

A bug, pebble or drop of coolant hitting a fan blade will also make a slight pinging sound, especially on a thin-bladed aluminum fan.

 

Thank you, all good suggestions. Solid fan.

 

Your finger hitting the blade makes a similar sound also.

 

If you pulled the belt off and it's stopped, then it's either the fan blade, or water pump.

 

Agreed. Remove the fan and pulley , check very carefully . A friend of mine had a solid fan come apart when he was revving his engine. Made a hell of a mess, thank goodness no one was injured or killed .

 

x2 on the motor mounts

 

Verify the pulley itself. Not just the bolt and pilot holes but inside the V belt groove.
Have experienced a 'ting' that became a 'knock'. Previous owner liked to tighten the begesus out of the fan belt. It actually caused the pulley to split in the valley of the V groove.

 

Twang sounds can come from a cracked Flywheel or Flexplate , common occurance on SBC

 

No loose wires flopping around?
There are some suggestions focused on aluminum fans..... but you haven't said. Steel or aluminum?
Switch a different fan in to test, if you can get your hands on one.
Get it pinned down and stay safe for the rest of the year and into the next one.

 

If this a SWP SBC check the water pump pulley center for cracks also they were so problematic that Chevrolet released a reinforcement for them.

 

Take the fan off and run with just the pulley. Noise goes away you know it's the fan.

 

Fluid drip from rad overflow dripping into fan ?


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The few cracked flex plates I’ve come across have made more of a knocking noise.
I would definitely remove the fan & w/p pulley & inspect closely as recommended as well as checking your motor mounts.


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On my last hot rod it was the one wire alternator. Noise would come and go. Dam china stuff!

 

No SBC, Industial 331 hemi.
I'll be pulling the grill and getting into and exposing the fan and pulleys. Thanks for all the suggestions. I did notice the water pump does have a minute bit of play in it as does one of the blades on the fan. Be a good time to install a new water pump anyway.

 

If one of the blades on the fan has some play you need to replace it immediately, if not sooner.

 

I had an old beater Dodge pickup that was my daily driver. One day I was under the hood, and something about the fan looked off to me. Closer inspection reveled one missing fan blade, gone completely! The area the blade broke off of had some few weeks old rust forming on the break. I was the only person that drove that truck, and I never heard anything, there was never any vibration, or any indication something was wrong. I have no idea when that blade came off, or how it missed everything under the hood when it left. It was a big block truck with a heavy duty radiator with a fan shroud the covered the entire edges of the radiator, trans cooler lines, and double Alt belts. No marks on anything. I figured I had a really lucky day in one of those previous few weeks, so I replaced the fan and went about my business. Gene

 

I used to drive a 64 corvette with a long fan spacer to get the clutch fan closer to the radiator. One day I was going through the gears in S.E. Portland when the water pump shaft snapped off. It fell forward and killed the radiator. I had just had the car painted so I was happy nothing came up through the hood.
My buddy, Tom had to put several chrome water pump pulleys on the small block in his 56 ford pickup. After cracking the 2nd one he went with painted pulleys.

 

Whatever you do, get it sorted. You do not want a fan to let go. On a 16" diameter fan at 3000 rpm, the blade tips are doing about 140 mph. It will turn to shit so fast that you will not see it happen, but you will certainly see (and feel) the effects................

 

And when you do find out what the problem is please post it , curious minds want to know.

 

I had a car do a similar noise. It turned out to be the alternator fan lightly touching the mounting bracket after an adjustment.

 

Is the blade close enough to hit if the frame has some flex? Mine did and I didn't find it till it went into the radiator.

 

Are the fan blades flexible? If so, they may be hitting something when flexed.

Can you try a new fan?

 

Check that the belt isn't starting to deteriorate