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I have a 2006 C4 with 49K miles and from a cold start, I began hearing this intermittent grinding noise on top of the regular engine hum during idle. This strange sound would go in and out just like how a locomotive would sound with intermittent whinning noise (which sounds very painful to me by the way). I took off the Air intake assembly to inspect the serpentine belt and the various pulleys, bearings and snubbers. They all seemed fine. I've attached a link to the video so you all can see.

thanks

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Does it do it with the "A/C off" button turned on? Maybe it's the compressor clutch or something? Really hard to tell from the video.

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Take the polyrib belt off and then run it for a few seconds. If the sound goes away it is highly likely one of the pulleys.

While you have it off spins each pulley by hand and see if any wobble or make noise.

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Replace belt with new. Not

a big investment.

Good luck with the pulleys.

Paul

Edited by PAULSPEED

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Painful sound during 0:32 - 0:35 in the video

I haven't tried it with the A/C on... I will do that.. thanks mxt_77

@Loren: Never tried turning the engine with the belt off...is that safe?

@Loren/Paulspeed: Brand new belt. I've physically taken off the belt and spun each pulley / bearing by hand....no wobble or resistance to rotation observed.

Thanks everyone!

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It is safe to run the end for a very short period without the belt. I suggest to keep it as short as possible since you will have no water pump or alternator for that period. All you are doing is verifying that the noise goes away without the pulleys etc.

You can test the pulleys for noise with the engine off. Just spin them with your hands.

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didn't get a chance to update you guys on this matter....didn't get back to it till last night but here are my observations:

- so i ran the engine for a few moments without the belt and the strange noise was not present which was great so it must be one of the accessories as all of you mentioned.

- next I spun each pulley / idler / accessory and nothing popped out of the ordinary in terms of resisting rotation or excessive play/wobbling.

- so i reconnected the belt and started the engine again to diagnose further. Took a really bright lamp and shown it on the fully exposed rotating belt pulley/idlers etc... as the engine was running. What i noticed is that there was a slight wobble (the kind only you would notice if you were to shine intense light on) on the water pump pulley and it synched with this aweful sound. So I went underneath placed my ear relatively near the pump housing which is visually accessible directly beneath the car. The noise definitely was coming from it because when i touched the housing (that's because I didnt have a stethoscope) I felt this vibrating sensation that again, synched up with the aweful noise. I also tried resting the tip of a long screwdriver and placing the back of the handle against my ear and confirmed this grinding vibration. Also tried this trick on the rest of the accessories (alternator, compressor, idler, tensioner..etc...) what I heard were slight and smooth vibrations - 10 folds less intense than with the water pump.

So I ordered a new pump arriving tomorrow morning and a video I found to perform the replacement...stay tuned..

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Glad to hear that it seems you found the culprit. Do you have any thoughts on why the noise seems to be intermittent? Does it maybe correspond to the thermostat opening/closing? The grind/squeal in your video seemed harsh and sudden, which is why I thought it might be related to something switch-activated (like the a/c & compressor clutch). Do you think there is a trigger that causes this grind, or is it purely random?

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This squealing sound was definitely random and "non-controlled" in nature. I am visualizing that the water pump impeller's bearings are somewhat halfway getting pulverized (sounds very painful) as fluid (coolant) continues to try to circulate. The grinding / squealing are probably caused by dis-membered ball bearings that are either stuck together as they try to rotate along the retainer and sleeve within the housing....very nasty!!!

Thanks again everyone for this brainstorming session. I'll keep you guys in the loop for any other developments.

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So sorry to bump this post, but did the water pump fix it? I figured the water pump spun faster than the crank pulley, so the periodicity of the grinding noise should be a lot faster at idle?

 

If anyone else can chime in, I have the exact same noise right now in my 996. It's driving me crazy, and I dare not drive the car almost.

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10 hours ago, Boxman90 said:

So sorry to bump this post, but did the water pump fix it? I figured the water pump spun faster than the crank pulley, so the periodicity of the grinding noise should be a lot faster at idle?

 

If anyone else can chime in, I have the exact same noise right now in my 996. It's driving me crazy, and I dare not drive the car almost.

A bad water pump can be very noisy. Remove the belt and turn the water pump by hand, it should be smooth and quiet. If not, it needs to be replaced. You can also run the motor while it is cold, for a short period of time, without the belt installed and listen for the noise (as suggested by Loren above).

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Posted (edited)

Well I ran it without the belt today, and still had the noise. It's almost 1:1 what OP showed, so I think OP never replied back because he grenaded his car:

 

I listened and recorded the sound, measured the periodicity of the grind and determined it to have a 'frequency' of 316 RPM.

 

Now, nothing in the car syncs up with 316 RPM. Idling, my engine runs 780 rpm. Camshafts go 1/2 that, so 390 RPM. The IMS shaft goes 0.67x crank, so 523 RPM. Couldn't think of anything else spinning at this weird fraction, until it hit me; the balls in a bearing go 1/2 the speed of the races, while the balls also have a shorter distance to travel because they're on a lower radius (more towards the center, smaller circle than the outer race), so complete 1 revolution 'faster'.

 

Correcting for the lower circumference the balls have to travel compared to the outer race, which is a factor 1.24, I came out on the balls inside the IMS bearing rotating with a frequency of 523 (shaft RPM) divided by 2 (balls go twice as slow) times 1.24 (distance in travel between outer race and balls itself) = 324 RPM. Which is very close to the 316 I measured from the sound.

 

So I'm pretty sure my IMS bearing is very close to grenading. And I think OP's was too.

Edited by Boxman90

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Yeah I already did before, like a week ago. There were ferritic metallic shavings in there before the grinding noise started presenting itself (about 300 km ago). The mechanic that installed the replacement bearing 13000 km ago convinced me it was leftover debris from the previous bearing, which was in pretty bad shape. Guess not.

 

I'll check my filter tonight probably once more, but I expect there to be metal shavings yet again. Then it's on to find out why this bearing failed so quick, since it was a dual row FVD Brombacher replacement...

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2 hours ago, Boxman90 said:

Yeah I already did before, like a week ago. There were ferritic metallic shavings in there before the grinding noise started presenting itself (about 300 km ago). The mechanic that installed the replacement bearing 13000 km ago convinced me it was leftover debris from the previous bearing, which was in pretty bad shape. Guess not.

 

I'll check my filter tonight probably once more, but I expect there to be metal shavings yet again. Then it's on to find out why this bearing failed so quick, since it was a dual row FVD Brombacher replacement...

 

If the engine had a bad IMS bearing, and someone simply put a new bearing in it without totally cleaning out the entire engine first, they were asking for another failure.

 

As part of a pre-installation inspection, we pull apart the oil filter and remove the sump cover on every engine, if there are ANY signs of ferrous metallic grit, we will not install a new bearing.  The engine needs to come out and apart first as once there is grit inside the engine it is going to kill the new bearing.

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1 hour ago, JFP in PA said:

 

If the engine had a bad IMS bearing, and someone simply put a new bearing in it without totally cleaning out the entire engine first, they were asking for another failure.

 

As part of a pre-installation inspection, we pull apart the oil filter and remove the sump cover on every engine, if there are ANY signs of ferrous metallic grit, we will not install a new bearing.  The engine needs to come out and apart first as once there is grit inside the engine it is going to kill the new bearing.

 

If the bearing works as intended, I kinda don't see why. That is, if the original philosophy of a sealed bearing was adhered to.

 

It was not fitted with a ceramic retrofit - with those I can understand the argument, since it's engine-oil lubricated. With a sealed bearing, oil should not be coming in in the first place, let alone the contaminants.

 

Add the full-flow oil filter and the tiny grits should be mostly gone after an oil flush or two.

 

Aside of that, how much work/cost in terms of parts is it to pull the engine apart? How far apart does it need to come? The pressure-fed journal bearings receive clean oil at all times, so I guess those can be skipped?

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1 minute ago, Boxman90 said:

If the bearing works as intended, I kinda don't see why. That is, if the original philosophy of a sealed bearing was adhered to.

 

It was not fitted with a ceramic retrofit - with those I can understand the argument, since it's engine-oil lubricated. With a sealed bearing, oil should not be coming in in the first place, let alone the contaminants.

 

Add the full-flow oil filter and the tiny grits should be mostly gone after an oil flush or two.

 

Unfortunately. the sealed bearings do not stay that way, which is why the oil influx washes the grease away.  Add fine ferrous grit to that oil, and the bearing quickly starts machining itself to death.  As for using a full flow filter and oil flushes, they may help, but there are far too many little nooks and crannies in these engines where debris can hide for a long time before popping out to kill a rod bearing or two.  Even during a normal (non failure) rebuild, special cleaning systems are necessary to get all of the junk out of these cases.

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So, after IMS failure with grit, an engine is pretty much written off then? A full rebuild costs a ton of money, which I don't have to spend unfortunately. I could live with periodic changes of the IMS bearing, as an interval maintenance part and something I could do myself. Using the standard bearing (not too expensive then), this should be a viable option for those who don't have the cash to take the entire thing apart?

 

I agree cleaning it is the absolute best course of engine. But I refuse to believe an engine cannot be kept in reasonably well state with periodic parts replacement and premium maintenance.

 

If I understand what you say correctly, any engine that had IMS failure - even if caught before total failure - will never work 'properly' if it's not fully taken apart which is basically a rebuild, and no IMS solutions are available that will not fail?

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3 minutes ago, Boxman90 said:

So, after IMS failure with grit, an engine is pretty much written off then? A full rebuild costs a ton of money, which I don't have to spend unfortunately. I could live with periodic changes of the IMS bearing, as an interval maintenance part and something I could do myself. Using the standard bearing (not too expensive then), this should be a viable option for those who don't have the cash to take the entire thing apart?

 

I agree cleaning it is the absolute best course of engine. But I refuse to believe an engine cannot be kept in reasonably well state with periodic parts replacement and premium maintenance.

 

If I understand what you say correctly, any engine that had IMS failure - even if caught before total failure - will never work 'properly' if it's not fully taken apart which is basically a rebuild, and no IMS solutions are available that will not fail?

 

Once the grit from an IMS failure enters the oil system, it is no longer a viable candidate for a retrofit.  At that stage, the engine is not a write off as most of the internal components are still in good shape to be reused, but a rebuild is necessary to prevent any further damage from the debris circulating inside the engine.  We have refused to retrofit engine's due to grit, and while the customer's took the cars elsewhere to have it done, some didn't make it 75 miles after the new IMS was installed.  Others made it further, but succumbed to rod/main bearing failures, cam shaft and lifter damage, etc., all the result of circulating grit.  Ferrous grit running around inside machined surfaces under load is not a good thing, it needs to be completely removed, and the only proven way to do that is pull the engine apart and run it through special cleaning procedure's.  Nothing else works.

 

If you are interested in learning more about this, LN Engineering has extensive information on their website.

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Posted (edited)

I know of LN Engineering and boy, have I read extensively these past 3 weeks. I suppose you work there and/or with them? They're not an option for me since I don't live in the US.


I'm not talking about the LN Engineering Retrofit - I know my engine would never for the life of it qualify for one since it's an open bearing. I have read the selection criteria. I would install a closed bearing, for which there are several options still.

 

So, again, just to be clear; IMS failure of any kind = engine totaled, by your standards? Since, put in the most simplest of terms, you can't use it without taking it completely apart, so the motor is beyond repair?

 

I chose those words carefully. You know as well as I do, an engine rebuild costs upwards of 7000 bucks. Even if components can be re-used. I don't consider that a 'repair', but rather 'building a new engine while re-using the main parts of an old one'.

Edited by Boxman90

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Frankly, you might consider taking some time to shop for a salvage engine with some known history and works, or even a wreck for cheap but again with a engine that can be demonstrated to work, then swap them. Make it a project. I've read about people keeping their eyes glued to the adverts and coming up with good finds. Might even be able to come up with something for the price of a Retrofit installation.

 

Then if you want to tackle a tear-down rebuild you'd be learning a crapload, as the college kids say.

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I have run an independant shop for many years, and while we do use LN Engineering products based upon their quaility and perfromance, we are not connected in any way.

 

Once we find ferrous metallic grit in the filter and/or sump, we will not move foward with that engine, it either needs to come apart or be replaced (which many people choose as it is often cheaper).  Too many people have tried too many times to recover a grit filled engine without doing so and ultimately failed.  Based upon those facts, putting new parts into an enigne that most likely is not going to make it very far is simply bad economics, both the labor and the parts are going to end up being wasted.

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Well, sure sounds to me like I've got a totaled engine sitting in my car then. I have the time and knowledge, but don't have the resources to rebuild or buy a working 996 engine. Engines I've worked on in the past survived a lot worse and were 9/10 times fixable. Seems like I bought myself a glass box, such a shame it didn't present symptoms when I bought it 3 weeks ago.

 

I know when to take the loss and walk away, I'll probably sell 'as-is with broken engine' and have learned an expensive lesson 🙂.

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