Just swapped out my pulleys on my S4 to serpentine to run an FD alt. Pulleys went it fine without having to remove main pulley hub. Broke one bolt to that pulley but replaced it with another of the same size. Now I'm getting some noise and vibration at anything above 5500 rpm.

Was wondering if anyone has run across this before. The pulleys are off a 13B-RE and so is the alternator which is the same as an FD I've been told. Don't know if it could be a bad alt bearing binding up at high speed or if it could be that the replacement bolt threw the main pulley off balance. Seems to be vibration free at below 5k rpm.

I did disconnect the pulley to the airpump but left the pump itself on because I have yet to get the block-off plates for it. Any ideas?? I'm hoping it wont be necessary to take the whole thing apart to try to find out.

 

did you check belt tension??? Is it within specs?

If you overtightened the belt, you could have wasted the bearing in the alt or the water pump

 

Thanks for the response there Icemark.
Yep checked the belt tension, Seems to be OK. Did a test by elimination and found out that it only gets the vibration when I hooked the radiator fan back up otherwise there was no sign of the vibration without it. Just ran the h2o pump and alt. and it ran normal.

Really puzzling. Revs ok to about 5k then it starts to vibrate up to 6k then disappears after that. Fan clutch slipping? I'm really at a loss here. Strange that it only occurs at that particular range of rpm's too.

BTW, I didn't touch the eccentric shaft bolt during the pulley upgrade, Just the 4 bolts on the main pulley. Shouldn't have any worries about the torrington bearing right?

 

No, you don't have to worry about the torrington bearing. Are you sure the waterpump pulley is flush with the waterpump flange? If its not true the fan will be incredible out of balance

 

I agree with the above, it may be the fan is off balance somehow.

Does the waterpump pulley from an RE fit a TII then?, is it simple to convert to the serp belt using RE bits?

 

Had to remove the accesory pulley off the water pump pulley to fit but yes the RE pulleys went on without any trouble. It's just really unusual that the vibration only occurs at a certain rpm range. Wouldn't an imbalance cause it to vibrate at all rpm's? I'm stumped and it's driving me nuts trying to figure it out.

 

It really depends on the frequency. I'm assuming you're using the clutch fan (so a quick way to by pass it would be to switch over to an E-fan), but in case you don't the reason why you don't feel the vibrations is what deals with something called resonance frequency.

If you're propellor is off balance, at low rpm's you won't feel the vibrations because there's greater vibrations running at their own frequencies that have destructive interference (meaning they nullify or nearly nullify) the wave. but as rpm increases the imbalance is spinning at a higher frequency and the amplitude will suffer constructive interference (IE: it's matching the internal vibrations of the engine rotors, for example)). IF you rev it higher you might push the fan and motor out of it's natural frequency which would return you to little to no vibrations or destructive interference. However if it doesn't you've just increased the amplitude and the frequency which adds more stress to the vibrating piece.

For a Better Explination as well as this

 

Thanks for the info. What I cant quite understand is that prior to the conversion to serpentine there was no problem at all. Clutch fan seemed to work with no vibration.
Don't want to go e-fan just yet. I'll have to see if there's any other possible cause.

 

have you checked the new pulleys are central on the shafts, you may find that the W/P pulley is slightly off centre if that is possible.

 

Is this the stock mechanical fan or an aftermarket fan?

 

It's the factory fan. Really stumped here about the vibration. Tried to isolate the problem again by removing the fan and the vibe disappeared. But I still cant understand why it would do that when it never vibrated prior to the conversion.