Started to hear an intermittent grinding noise
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Northstar Engines and System Technical Discussion Discussion, Started to hear an intermittent grinding noise in Cadillac Engine Technical Discussion; from the front of the motor on my 1994 STS Seville. Yesterday I was having a problem with my alternator ...
  1. #1
    therodman is offline Cadillac Owners Fanatic
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    Started to hear an intermittent grinding noise

    from the front of the motor on my 1994 STS Seville. Yesterday I was having a problem with my alternator or so I thought, turned out it was the battery cable. I take my daughter to school this morning ( 2 miles ) and when I get home I hear a grinding noise coming from under the hood. I listen by the front of the motor, passenger side where the balancer is located, I'm calling that the front. The noise would be there for about 1 or 2 seconds and then go away for a few seconds. It sounds like a metal line is touching a pulley while the car is running, push the line into the pulley and pull it away, that's what it sounds like.

    I'm listening trying to figure where it's coming from, the tensioner pulley looks and feels okay, the idler pulley the same so I rev the engine. While the RPM's are increasing the grinding would stay constant, when the thrust is reversed and the RPM's are coming down the grinding would go away. Are there timing chains for the cams, are they gear drive, what could be in the front of the motor to cause this noise? It's not real loud but just noticeable with the hood closed.

    Now the good part, while I'm revving the engine I finally give it a few good blasts ( maybe 4-5k RPM's ) and the noise quit, gone! It almost sounde lke a small pebble may have been stuck next to one of the pulleys, maybe a nut, screw, who knows and when I revved it good, it spit it out. I have no idea how the cams are driven, I assume chains and would also assume there is a chain tensioner, maybe the chain tensioner was sticking if that's possible. That is what is really sounded like, a loose timing chain scraping the inside of the cover when the thrust is almost neutral.

    Someone may ask, if it's gone, why are you asking these questions?
    1. I've owned and worked on cars long enough to know that if you have a noise, or say a knock, a tick and it goes away, it's coming back. You can bet it's coming back sooner or later, probably sooner. So, that being the case, I want to be somewhat prepared when it does come back. The only way it doesn't is if it was an object of some sort that was "laying" up against either the power steering pulley or crankshaft balancer pulley and it was dislodged when I revved the engine real high.

    I know I can find an illustration of the inside of a 1994 Northstar engine but it won't tell me what others may have experienced or what an expert mecahanic believes the problem could be or have been!

    Any comments would be most appreciated!

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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Started to hear an intermittent grinding noise

    Can't help much on what or where the noise was, but the cams are chain driven. Open the oil fill cap and look in with a flashlight and you'll see one. There are nylon tensioners on them and they will last the life of the engine.

  4. #3
    therodman is offline Cadillac Owners Fanatic
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    Re: Started to hear an intermittent grinding noise

    Thanks Ranger, I'll look inside tomorrow and go from there. So far the noice hasn't returned so maybe it was a piece of trash that had gotten up against one of the pulleys.

    As far as the cam's being driven by chain with a nylon tensioner, I'll take your word that they will last the lifetime of the engine. I'm assuming lifetime is in the 200k range, at least I beleive my engine will go that far, easy. I have about 108 or 109k and it's like brand new, still pulls very hard and doesn't burn 1 speck of oil.

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    Ranger's Avatar
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    Re: Started to hear an intermittent grinding noise

    We have had people here with over 350K. There is a thread somewhere entitle "Who Can Beat Me".

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    32vmonte is offline Cadillac Owners Member
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    Re: Started to hear an intermittent grinding noise

    A/C compressor clutch? I have had this problem before but on a 98 monte carlo. When the defroster is on the A/C cycles on and off because it is used for removing moisture in the cabin. Well when it would turn off the clutch would make this horrible metal grinding noise.

    Like you said it stayed constant when you rev the engine. One day it went away and never came back.

  7. #6
    therodman is offline Cadillac Owners Fanatic
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    Re: Started to hear an intermittent grinding noise

    The grinding noise that I first mentioned has never come back. What I have now is a whining noise, same area, the front of the motor. I've checked everything that turns with the belt and am quite sure that the whining has nothing to do with any of those parts. It's coming from the front of the motor and is quite noticeable when the motor is cold. When it wamrs up the whining noise almost goes away.

    It's not the power steering but sounds a lot like a bad power steering pump! What is in or near the front of the motor that could casue that whine. It's a 1994 STS that I'm talking about, around 110k miles.

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    Ranger's Avatar
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    Re: Started to hear an intermittent grinding noise

    The water pump is on the rear of the motor and is belt driven off of the left bank intake cam. Check the belt tensioner.

  9. #8
    therodman is offline Cadillac Owners Fanatic
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    Re: Started to hear an intermittent grinding noise

    Ranger, That seems like a reach but I'll certainly give it a try. The whining doesn't sound like a typical pulley bearing going out. Any bearing be it the alternator, belt tensioner, a/c comp, all create more of a grinding or squeeling noise, most of the time! It wouldn't surprise me that it's something I haven't experienced before. When you think you've seen or heard it all, a new noise will show up.

    This noise sounds more like a gear drive for a cam or a transmission with a clogged filter. There is a local transmission shop that said they would diagnose the problem for no charge and felt certain they could locate the problem. I believe it's a young mechanic that's a little over exhuberant and have my coubts about their ability to locate the problem without removing parts one at a time.

    In the morning I'll chekc that tensioner and would be tickled if that was making the whining noise.

    I'll check back and keep you updated.

  10. #9
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    Re: Started to hear an intermittent grinding noise

    rodman, I just posted an opinion in a similar thread next to this one - by restoman.

  11. #10
    therodman is offline Cadillac Owners Fanatic
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    Re: Started to hear an intermittent grinding noise

    Submariner, I read your post from the other thread and although that's not what I want to hear, I'm starting to believe that the problem is internal to the front of the motor and waht you've described with the timing chain slipper, that could very well be the problem. It's nearly time for an oil change so I'll get a good look at the oil and filter for plastic deposits. I guess if the plastic is worn away then the chain would be rubbing against a metal part thus making the whining sound that I'm hearing.

    I'm pretty sure without asking but I'll ask anyway, it's probably a big job getting at the slipper for replacement?

    Ranger, I did look at the water pump tnesioner and in fact, removed the belt, the whine was still present. I left that belt off and removed the serpentine belt and still the whine was present.

    I may try and post a little video clip with sound so ya'll can hear the noise even though I believe the problem has been narrowed down. It would be more for future reference and aslo to see if I can do it.

    Thanks, I will keep ya'll posted......

  12. #11
    Ranger's Avatar
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    Re: Started to hear an intermittent grinding noise

    Is there any chance this "whine" is a vacuum leak whistle from the manifold over pressurization valve?

  13. #12
    therodman is offline Cadillac Owners Fanatic
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    Re: Started to hear an intermittent grinding noise

    Ranger, I guess it could be that valve your talking about and what makes me think that is the whine went away a few minutes ago on the highway. When I got off the highway, the whine was gone. WHen I accelerated, it was not present until I pushed harder on the accelerator, about half way down with the pedal, it started again. I caould make it go away with light pressure on the accelerator and make it come back with more throttle.

    Where exactly is that valve on a 1994 STS? I stopped at a garage on the way home and the mechanic listened and pointed to where I hear the noise, the front of the back bank of cylinders next to the firewall. It would be where the camshaft sprocket would be if the cover wasn't there. He thought it was a camshaft tensioner which I was beginning to think myself.

    If it was a tensioner, how could it go away and then come back? Seems a mechanical problem would be constant where as a valve could be opening, sticking, staying closed, and therefore the noise would come and go.

    I have to run but I'll check back shortly.

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    Re: Started to hear an intermittent grinding noise

    The cam chains have hydraulic tensioners which ride on the engine oil pressure. It's possible that you could alter or alleviate the problem with an oil/filter change. If that doesn't do it, then you're possibly looking at going into the front of the engine timing cover (chaincase). Not fun.

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    Re: Started to hear an intermittent grinding noise

    The over pressure relief valve is exactly opposite the TB. It's tucked back in a hole behind the P/S pump. If you hear it at idle you can listen in there with a stethoscope or rubber hose or reach in with a stick or long screwdriver and press on the valve (flapper door) to add tension and see if that quiets it down.

  16. #15
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    Re: Started to hear an intermittent grinding noise

    What you describe really sounds like the a/c clutch to me. Try turning the a/c off and see if the sound becomes constant. If so, there's your culprit.

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