Hoping someone has run into this problem before as it makes absolutely no sense to me.

Car is a 1989 S4 Automatic

The problem I am having is the idler pulleys below the crankshaft (2 Rollers on Pins) are making a harmonic hum noise like they have a bad bearing. The noise seems to be certainly coming from the bearings/belt in this area as I can put my stethoscope on it and it seems almost certainly coming from this part.

I should note the bearings feel fantastic and I even have a 2nd Brand New from Porsche Rollers and they are also making this same harmonic hum.

I have tried to set them so they have some play on the pins as well as with the tight so they can't slide side to side but nothing seems to improve the sound.

I have tried belt tension from 5.0 to 5.4 to see if maybe something odd was going on but again not helping.

Got any Ideas?

Thanks
-Fishey

 

Those two little idler bearings are there to help keep the belt on the drive gear should it decide to grow a little on engine speed change. Under normal circumstances they should not contact the belt. The two rollers have little sealed ball-bearings inside the roller shells. The little cast console slides onto pins in the block just below the gear. Little circlips (I think Jim Bailey called them "Jesus Clips") hold the little cast console onto the pins. The fit is quite loose there, so I packed the console holes with a very thick grease to keep vibration wear to a minimum.

Noise you hear by stethoscope there is likely to be block noise coming through the pins, rather than local harmonic noise generated by the bearings in those rollers turning. The mass is too small to make any significant noise that might transfer to the front of the block. At most it would be a very high-pitch whirr if the roller is actually spinning with the crank and belt.

 

You can do away with them if ya use PorKen's tensioner. Mine are on a shelf in the garage in a box.

 

the posts might be bent upward giving contact , which really shouldnt happen. they are not that critical ... maybe just shoot some W40 in there and it might quiet them down. (or some dirt to slow them down. )

 

Can, I get away with just removing them to diagnose if they are infact the source of the noise?

 

Yes. They are there to help maintain belt contact when you suddenly increase the engine speed, when the tensioner might not respond quickly to any slack from belt stretch, therefore allowing that slack immediately downstream [to the left] of the crank gear. If you are just going to let the engine idle while you listen, there should be no problem.

 

Probably not the idler(s). Hopefully not waterpump.

Betchu it's the airpump. Try removing its belt.

 

Random off topic:

I always heard them called "Jesus Christ Clips' because they need to be pushed very evenly to get them off, and once they get past the middle of the pin, they end up flying a long way. Then the tech says "Jesus Christ! Where did that go!?!"

 

It makes the noise with no belts on, and water pump is new and appears to be dead quiet along with every other roller that is also new.

We are going to use the single roller style to see if it changes anything.

 

So, can the crankshaft pulley be installed backwards? and or the orientation of the belt guide washers?

 

My 88 has been running for 1600 miles without them. I used the stock tensioner. I don't think they exist before 1987? Not sure, but it's fine without.

 

They are there for the 85 year for sure. Mine looked like they had never seen contact with the belt when I pulled them off this year. I actually forgot about the ball bearings until after everything was buttoned up. Hope they aren't critical.

 

The crank gear is symmetrical. The belt guides should be installed convex to the gear, meaning the washers should curve away from the gear. The harmonic balancer can be installed backwards but you obviously want it installed correctly, with the numbers readible from the front. The crank bolt washer can be installed backwards, but you want to install it with the lip over the crankshaf snout, not towards you.

 

So, I tore it all apart.

New Tensioner Pulley seems to be making noise and somehow being amplified off the lower idlers.

So, glad that new part was messed up out of the box. (feels smooth if you spin by hand) bastards!

 

Just read this thread.

I have this noise probably for the last 10k miles and it does seem to be coming from front low down on the engine, but I removed the two bottom rollers 20k miles ago when I fitted the PK tensioner, I have removed the accessorie belts one by one but that made no difference.

The noise is not audible at idle, most audible around 1500 and then seems to fade out as the revs rise.

I'm in the, let it develope stage at the moment.