Top-Gun

This ones got me stumped. I installed an RS fan hub (OEM Porsche) on my car and since then I've noticed a rattling sound that occurs only when the car is started from dead cold. The noise lasts a couple minutes until a little heat gets into it then goes away. It's only noticeable at idle, with any revs it stops.

At first I thought I had a loose heat shield but I've confirmed the noise is coming from the pulley/fan/alt assembly. I've ruled out the following thus far;

- Removed the A/C belt, no change
- Removed fan belt, noise goes away, thus it has to be something to do with the fan/alt/housing
- Inspected the fan blades for evidence of rubbing, nothing
- Swapped in a new OEM fan, no change
- Confirmed the mating faces of the hub, fan, and pulley are flat and clean
- Rebuilt the alternator including new front and rear bearings and a new voltage regulator/brushes, no change
- Removed and inspected fan housing for cracks or anything abnormal, nothing
- Checked inside the engine shrouding for anything loose that could rattle, nothing
- Swapped the pulley halves (front to back), no change
- Confirmed with Krikit that belt is tensioned properly
- Installed new OEM Porsche belts, no change
- Confirmed all fasteners are torqued to spec and that the fan housing was pushed towards front of car while tightening strap as per manual

I must have installed and removed the alternator/fan/housing 10 times at this point. I'm at the point where I feel this has to be a characteristic of the one piece fan hub?

Any insight is appreciated.

AOW162435

Removing the fan assembly once, let alone ten times, to chase an issue is no fun.

I’m not sure how the hub itself can be the source of the rattle - it’s a one-piece machined item that’s clamped between the spacer and the shaft nut, correct?



Andreas

Top-Gun

Correct, its dirt simple, adding to my frustration ha.

All I can hypothesize is that the fan now spins slower at idle, perhaps it's a resonance of the assembly or something. I cant explain how the thermal part factors in though.

I'll shoot a short video and post it too see if that helps generate any ideas.

Thanks.

Endoman

I had a similar noise with the RS pulley more of a click when it was cold. I replaced the assembly with a Clewett Serpentine kit and the noise went. When I removed the crank pulley one of the balance weights at the back of the pulley was ever so slightly loose.

Ivan J

Did you rule out the plastic fan-belt sensor pulley?

AOW162435

Yes, it does spin slower. I would think that a speed-dependent resonance would present regardless of component temperature (maybe not).

I installed the Clewett serpentine setup in my 993 four years ago and have since installed five more for other 993 owners. The Clewett setup spins the fan faster than the RS setup but slower than stock. I’ve yet to experience any unexplained noises using these.

Are you certain that the alternator body is completely seated within the fan housing, and that the rear cooling fan nut is snug?




Andreas

Churchill

By gumdrop, I also have this problem. Except I installed the RS hub 10+ years ago. The noise is a rattle but also a bell type sound, like something is ringing the alternator housing. I thought it was the alternator bearing going, so I rebuilt the alternator. Still there. No idea what's going on.

AOW162435

If you hold a steady 1000 rpm idle, does the sound persist?




Andreas

pp000830

Could the rattling be the chain in the timing chain housing as its slack snaps a little at a too slow idle. The ringing can be a fan blade dinging the fan housing.

P-daddy

I had the RS single belt set up several years ago, but experienced no odd noises.
You have the updated pulleys?

nine9six

Andy,
The pulley, which is a different diameter, is driven by the crank, which drives the cams via the cam chains. The engine idle should not change utilizing the RS pulley, only the rpm of the alternator/fan. The ringing could very well be a rubbing fan blade.

I'd like to put a dial indicator on that new RS pulley, in the y and z axis, since there were no noises or issues with the OEM pulley.

AOW162435

Whistling noise



Andreas

nine9six

Whatever...Lol

Magicscott

I have the same sound after installing a new alternator, RS Pulley, and painting the fan and housing about three years ago. Sounds like a ringing sound coming from the fan when the engine is cold. Ringing goes away after engine warms up. I couldn't figure it out after taking everything apart about 5-6 more times so I'm living with it until "next time"!

Magic

911PERVY

He wont have one......................................so yes