montreal-1

Hello

After a recent 10 hour drive in my wife's 98 Sentra, we were treated to a new noise coming from the engine compartment, a high pitch sound that varied in frequency with the engine speed.

It took a while to trace it, but here is how I approached the problem.

First I removed the exterior power steering V-belt and that did not stop the sound. Then I removed the inner V-belt and the engine was very quite. Running the engine without an alternator belt doees not throw an OBD-II code, only the dashboard red light will come on.

That implied to me that the sound was coming from the alternator, the AC compressor, or the idler tensioner pulley. Each of these three items turned over easily by hand without any resistance or noise. But when the crankshaft is turning at 3000 rpms, these accessories turn at the same, if not higher rpms, and the ball bearings can make a noise at that speed.

The easiest item to remove was the tensioner pulley. I took it off and cleaned up the dirt and oil and put it back on and the noise was still there. Then it took this same pulley off, but this time along with the bracket that holds this tensioner pulley and the combination looked OK. But just as I was putting this combination back, I noticed that there was a small play in the bearing of this pulley which is visible when the pulley is firmly attached to its holder. If I put the holder in a vice, then I can wiggle the pulley ever so slightly on its axis. That left me assuming that there had been some wear in the inner groove that the balls in the bearing travel on.

So I went looking for a replacement bearing to the original NSK 6301DULX. It turns out to be an alternator type bearing.

I ended up visiting an industrial supplier of bearings and purchased a SKF 6301-2RS1.

To get the old bearing out, I used a socket from a wrench set and an old hand-wheel driven book press. Because of the smaller hole opening on the side of the pulley wheel that you must press against in order to extract the bearing, the largest socket I could use ended up pushing against the softer section of the bearing, where the plastic seal is located. Pushing the socket into this area destroys the seal, but my goal was to extract the bearing, not keep it intact for reuse.

Fortunately under the plastic seal are the 6 bearing balls which will receive the full force of the socket pressing down on it and these balls transmit the force to the outer ring of the bearing. The old bearing did not want to budge, so I sprayed some penetrating oil over all visible bearing surfaces and tried again. This time it came out with much effort.

There was a certain amount of rust that had formed between the pulley cup and the old bearing and I cleaned that up and put a layer of grease in the cup ready to receive the new bearing.

The next challenge was to press the new bearing into place making sure that the press would not damage the side of new bearing. I did not want to apply any force to the inner ring of the bearing, when it was only the outer ring that I wanted to apply force to.

My first error was to place a small block of hardwood over the new bearing while in the press. Somehow the wooden block shifted under the pressure and the new bearing started to go in skewed off axis. I removed the block and allowed the press to apply pressure directly to the new bearing and it started to go in correctly.

The press, with its one foot square platten, could only insert the bearing about 75% of the way because of the geometry of the pulley. Using the old bearing directly over the new one and then re-pressing, allowed for a complete insertion. The internal grease in the new bearing has more viscosity than the old one, so it spins not as easily as the old worn bearing, but there is less play between the parts.

Back on the car, the new bearing did not make the motor as silent as when there were no belts on the car, but my wife and I agree that the high pitched sound is much less noticeable.

I conclude that new or old, all the bearings in the belt driven accessories will make some kind of high frequency noise due to the fact that they spin at similar speeds to the crankshaft. The idler tensionner pulley having a much smaller diameter than the other pulleys, spins at the highest speed, so it is most likely the source of the highest pitched sound, be it load or soft.

Apparently, a number of auto parts stores don't bother to sell the tensioner bearing alone, so you often end up having to purchase the bearing already installed in a new pulley wheel. At least you don't have to search for an adequate press.

Hope this helps others.

 

montreal-1

UPDATE:

Now that my wife has had a chance to drive the car at regular speed within the city, our consensus is that the original noise is still there.

Which means that it is probably either the alternator or the AC compressor.

Within the alternator, it could be a bearing(s) or even a carbon brush.

I know the alternator comes apart pretty easily, but I have no idea if the bearings are press fitted tightly into a cup, or just held in place by a couple of bolts?

Powderfinger

This indicates to me that the problem isn't belt or pulley related. If the noise is unaffected while coasting in neutral with engine idling then I'd look for something in the driveline....Maybe brakes, wheels, axles, or even cv joints. Are the boots ripped? Does the noise go away or change pitch when you apply the brakes or negotiate turns?

montreal-1

While having my front seal replaced at the dealership today, I asked the mechanic for his opinion as to where the high pitched sound was coming from.

He said it was the idler tension pulley, the same pulley for which I changed the 8 year old original NSK 6301-DULX bearing for a SKF 6301-2RS1, last week.

So I have written off to SKF to ask why their new bearing sounds just like the old NSK bearing.

Nissan does not sell the bearing, only the pulley/bearing combination for 7 times what I paid for the SKF bearing.

It may be that it was time for the NSK bearing to be changed due to the sudden introduction of the noise last month, but if the noise in the new SKF bearing is normal, then I may just leave it as is. My only real concern was that I wanted to make sure that all bearing due for replacement were indeed replaced. That that is what has taken place.

TAZTECH

if it does it when it is idling, then use a stethoscope(similar to a doctor's) and chace down the noise. If the car has to be in motion you can use chasis ears. If you throw parts at it, you may never fix it and waste a lot of money.

montreal-1

The mechanic at our dealership who changed the front crank seal today said he placed a screwdriver between his ear and the idler pulley, as well as the alternator and AC and he said the loudest noise was coming from the idler pulley.

I am upset because I went to a lot of effort to carefully press out the old bearing in this pulley last week and now I am being told (and I believe him) that the new bearing sounds just like the old one.

Could it be that many 6301 type bearing can be compatible, but manufactured in a way that some are noisier than others. Clearly, the original 8 year old bearing was quiet up until last month, following a 20 hour non-stop trip. For the noise to suddenly appear after all this time means to me that the original bearing may have degraded during the trip, so changing it was a wise move on my part.

But for the new bearing to make that same noise may not be a sign that it is also defective or worn. It may just be the way the SKF version of this bearing sounds.

I am waiting for SKF's answer and I will post any news.

funkpacket

I was curious if there has been any developments since your last post montreal. I have a similar noise coming from the crank side of my ga, and im interested to see how this plays out

montreal-1

After no answer to my e-mail to I sent to SKF, I telephoned them and their CSR engineer stated that a bearing can be damaged in at least two ways - by acquiring one or more flat spots on one or more balls (or rollers), or by having the bearing partially of fully seize up.

When the idler pulley bearing FULLY seizes up, then the bearing may possibly spin on the shaft that supports the bearing - metal on metal and this can create a high pitched sound. If this was happening, given that the idler pulley spins counter-clockwise (opposite to crank pulley), the nut that normally secures the idler pulley to its shaft would probably fly off (or at least have to remain loose) and the squealing noise would cease as soon as the idler pulley drifted off its shaft and fell on the road.

But if that nut remains tight and holds the bearing's inner race securely to the shaft with no relative movement, then this bearing could not be FULLY seized up because some other part of the bearing would still have to be sliding (with difficulty).

So if the idler pulley bearing is FULLY seized and the nut is still tight preventing the inner race from spinning freely on its shaft, then this pulley would end up completely locked and the belt would break.

What if the idler pulley bearing is PARTIALLY seized, that is, the balls don't roll properly in the grooves? In this situation, there could be metal on metal scraping and thus making a high pitched sound. But if this is your case, then if you take your belts off and then you turn over your idler pulley by hand, you should be able to feel some resistance caused by the ball mechanism which is partially seized.

As for the situation where through age or poor installation , there is a flat on one or more balls, the SKF engineer said that this could cause a vibration (noise) but the frequency of the ball(s) vibrating would not be that high due to the grease damping out some of the vibration.

In my case, my old and new bearings turned over by hand easily so it is not likely that my old bearing was partially seized at the time when I replaced it 2 weeks ago. And after looking at the installation instructions from SKF, I believe I applied the pressure correctly to the outer race so I do not think I added any flats to the new SKF bearing during insertion in the pulley.

I am left to conclude that my Nissan mechanic who examined my car (for another problem) may have errored when he said he detected the high pitch squeal noise to be coming from my newly installed SKF bearing. He used a long screwdirver between his ear and pulley, and I do not doubt that he heard the loudest noise coming from the idler puller compared to the alternator or AC, but I have to wonder if the high pitch noise in question was coming from the alternator.

I have the choice of getting an old second-hand idler pulley from a junk yard that spins freely and trying it out just to confirm my theory, or I can open up my alternator looking for a worn out, but still functioning, bearing which might be the source of the high pitched noise.

Looking back, perhaps I should have tracked down a genuine NSK 6301-DULX bearing instead of a SKF substitute, just to eliminate any doubt about their compatability.