johnC5

Engine Experts: What is this noise? The noise is coming from the engine, and can be heard a few feet from the car with the hood closed:
http://www.brightland.com/cf/video/Z06Noise.wmv (Large: 1.1MB) http://www.brightland.com/cf/video/Z06Noise_small.wmv (Small: 732KB)

nfshotrod

Get it to the dealer it is knocking.

torchedz

sounds like it might be a header leak, do you have headers. You better hope is is that and not a broke piston or valvespring, if it is stock take it back to the dealer. Good luck. It is not going to knock at idle unless the piston is broke.


[Modified by torchedz, 1:01 AM 2/19/2003]

TexasRedZ06

I'm no engine expert, but I do hear the noise. Doesn't sound all too different from my Z06 when its at cold idle. Might just be piston slap or normal valvetrain noise from the rollers. The piston slap is more noticeable when the engine is cold.

How long have you had the car??

Has the noise always been there??

Does it happen after the car has fully warmed up??

Any difference when the clutch is depressed??

Does it get louder or faster under acceleration??

Did you notice the noise after a recent race or did you redline the engine??


[Modified by TexasRedZ06, 7:11 PM 2/18/2003]

johnC5

No headers. Car is stock.

johnC5

1. How long have you had the car??

About 8 months.

2. Has the noise always been there??

The noise was there since day one (car had 34 miles, purchased new from dealer). Initially, the noise was only noticeable during startup/cold, and then only intermittant. Noise seemed to go away once warm. Multiple dealers called the noise normal.

3. Any difference when the clutch is depressed??

No. Not clutch related. Sound is coming from heads or block (hard to tell with hood open due to all the other noise).

4. Does it get louder or faster under acceleration??

Yes, it gets faster. Hard to tell if it gets louder as other noises drown it out. Initially, the sound went away when driving (only noticeable during idle). Now the sound is always there and noticeable during part-mid throttle. At WOT, all other noises drown it out.

5. Did you notice the noise after a recent race or did you redline the engine??

The car was at the dealer, and one of their tasks was to listen to the noise (which was minor). After the dealer put 23 miles on the car, the noise appeared to become permanent. The car was brought to the dealer spotless, and returned with the back of the car covered with black material. The transmission also appears to make more noise and seems to behave differently (I drive the car frequently and notice subtle differences). There was an issue with the dealer regarding who was driving this vehicle (their stories didn't match). It's possible they did something to the car when driving it. It could also be coincidence, and a small defect has become more pronounced.

Is this sound normal?


[Modified by johnC5, 6:33 PM 2/18/2003]

TexasRedZ06

Well the noisy valvetrain and the piston slap are "normal" for the Z06. The black stuff on the rear of the car doesn't sound good. Is it oily?? It could be just airborne dust from the service center. Clean it off and make some freeway runs to see if it comes back.

Obviously you aren't throwing any codes, right?? You've checked the DIC... haven't you? I can hear the slap and the rollers in my Z06 even after its warmed up and at cruising speed. Other Z06s I've heard have been a little quieter and a little louder, so again, it may just be "normal" engine sounds that you're hearing. The Z06 does make some weird noises. Your tapping noise sounds louder than mine, but mechanically no different.

I would be more concerned if you notice any performance degradation, DIC codes, oil consumption or a reoccurance of the black stuff on the rear end.

If it were me, I would post on the Pacific Region and get a recommendation for another dealer to take it to for a second opinion, especially if the noise is getting louder. Could be a bent pushrod or a defective bearing.

Hopefully others will chime in............

johnC5

I believe the black stuff on the rear may be oil. It looks like it just used a quart in about 1500 miles (initially it used about 1 quart in 3000 miles). I don't want to sidetrack this thead on oil use, though (I am familiar with the typical causes and fixes). I mentioned it as I can drive the car for over a week and not get the rear end as dirty as the dealer did in one day (like you said, could be shop dirt).

So far no apparent performance reduction, no codes.

The tapping sound appears to come from just one engine element (as opposed to many).

What is interesting is that the sound has changed and gotten louder. I first noticed the change after getting the car back from the dealership. Perhaps coincidence. Just trying to figure this thing out. :cheers:


[Modified by johnC5, 7:52 PM 2/18/2003]

LingenfelterC5

Take it to the dealer

pdvale

Before I bought my 02 I test drove an 01. The 01 engine sounded like a bag of nails, I was a alittle concerned. My 02 only has a very slight chatter noise, nothing like your video. Definately take it to get looked at.. might be ok, but it doesn't sound too good.

good luck,
Paul.

johnC5

Here's an interesting TSB from C5-TECH. Sounds like it could be the problem:

TexasRedZ06

So the o-ring causes lower pressure that results in the lifter noise?? So then you would notice lower oil pressure at speed, right?? Checking that o-ring on the pump would require dropping the whole front steering assembly to get at the oil pan, wouldn't it?? Holy crap what a mess :smash:

Could be a valvestem seal(s). On a different engine, I had one of these pop off its seat, causing a ticking noise, a warped valve and higher oil consumption. However, checking these on the LS6 would require a lot of pull apart to get to the valve covers. But a stethoscope used by a tech could determine this one fairly easy.

Just trying to figure out how a tapping/ticking noise, higher oil consumption and oil residue could relate. Is it possible that you just have a snapped piston ring?? This would cause the above. Compression test would work for this.


[Modified by TexasRedZ06, 2:55 AM 2/19/2003]

rwd

Is there a reason you didn't video the car with the hood up, i.e., is the noise more noticeable somewhere else? Moving the cam around the engine compartment might be instructive. I realize it's difficult when you can't manually control the record volume.

I'm assuming it's related to engine speed and not road speed.
It sounds excessive for 'normal' to me. It does sound valve-train related.

You wouldn't need a stethoscope to do some preliminary investigation.

If you put something solid, like a wooden dowel or a long screwdriver, against the engine and the other against your ear, the noise will be transmitted directly to your ear without the extraneous sounds. By moving the rod around, you can locate the source. This also works with alternator bearings and anything else. It's an old trick for identifying bad lifters, etc.

Do you have any pics of the material that was on the rear of the car? Was it evenly distributed or was there more around the exhaust area? Is there some (or anything else unusual) on the inside of the pipes? It might be worth checking or sticking a finger in and/or comparing to other Z's (even ones on lots).

Do you have any info on what the dealer actually did or can you talk to the tech? I'd start looking for another dealer for a second opinion, and if you can't get any leads, look for one that sells a lot of vettes.

If it's an O-ring thing, the noise may move around, and I wouldn't count on the oil pressure reading being low. Good luck.

johnC5

Thanks for the tips and feedback. :cheers:

johnC5

Yes, I video-captured the car with the hood closed to make the sound easier to hear (the hood acts as a low-pass filter, cutting high frequencies). With the hood open and up close, it's much harder to hear the noise. I have fancier audio gear, where I can adjust the level, and can also filter and adjust the audio with SoundForge. But, I wanted to keep it quick and simple (I used a Canon G1 digital camera's video capture to make the video).

I just washed the car. I'll photograph the back, then again after driving for a while. Initially (first few thousand miles, the exhaust tips stayed very clean. They're now pretty black (at 7000+ miles)). The distribution of black material seemed pretty even. In the past, the back of the car was covered with brown/gray material that washed off easily. This last car wash was more difficult as some of the black particles stuck to the paint. Additionally, the black particles where much larger than the usual dirt/dust.

Thanks for the tips. :cheers:

johnC5

First, car does not seem to be using oil. Black material appears to be coming from the road.

Second, dealer heard the noise. I showed them the TSB. The service manager stated that he was aware of the TSB, and the GM rep stated that the O-ring change will not fix the problem.

Is it possible to get a GM engineer to view my video?

rwd

I figured that's what you were doing with the video.

I'm assuming what you're saying is the dealer's position is that the noise is normal, and that therefore the fix won't work? If the fact that it is normal is due to a lot of them having the same problem, the logic is irrelevant.

If there are still other dealers you can try, that'd be an option. Although the tsb is not limited to vettes, their experience baseline may be skewed. Maybe a tuner or performance shop might have some ideas.

Clearly, you need more info. If you haven't tried listening with a dowel or the like, I suggest trying that next. If it's related to only one cylinder and the others are quiet, that would seem to be something other than 'normal.'

Another alternative (which you may have done already) would be to listen to and/or video a number of other Z's or other affected cars/trucks for comparison. Similar video of a number of cars that were significantly quieter- or more precisely, uniformly noisy- might be useful. To me, the issue is not that there is noise, but that the noise is not uniform, i.e., from every lifter, for example. I suppose it's remotely possible it might be a valve lash adjustment.

The material on the rear may be irrelevant and kicked up off the road. Oil flecks would typically be a whitish,bluish or grayish. Comparing the color inside the exhaust tips with that of other Z's might be useful; they should be dry and a light gray.

But if it's aeration, the noise and a slight loss of performance would be about the only noticeable symptoms- unless something went seriously wrong. It really does sound like a collapsed lifter, as the tsb suggests.

Clearly, air in the oil is not good. Any information you can get from GM regarding how they determine what is abnormal would be useful. Inspection may be the only solution.

johnC5

The dealer admits (at this point) the noise is not normal. They stated that they'd do the TSB "fix", but also stated that it would not work (apparently it requires taking apart the entire front end to get to the oil pan). They don't believe the problem is aeration of the oil. They said to document the problem (which I did) and if there is an even bigger problem later, it's covered by warranty.

A buddy has a 2003 Z06 (just a few months newer than mine). His makes all the "normal" Z06 noises, but not the ticking noise as shown in the video.

The exhuast tips are black. A few months ago, I noted how absolutely clean the tips were, and had a bet with a Toyota mechanic stating how clean the tips were. He wiped his finger around the inside tip and got no material on his finger. He then stuck his finger into the actual exhaust pipe and got a little black material on his finger (I won the bet about the exhaust tips being clean, though). I'll recheck the tips and see if they have changed.

As for having a Corvette Tuner listen: he's stated since day one that the noise is not normal. He was the first to point out that the noise has gotten louder. I'll stop by his shop and borrow a stethescope and see if I can find the source of the noise. He states that it sounds like a bad lifter or incorrect pushrod length.

If aeration of the oil is not good, then driving 7000+ miles with aerated oil would be very tough on all the bearings. Additionally, all thoses miles of hammering on the cam and lifters may have caused mushrooming/deformation (perhaps the cause of the latest noise?).

As you stated, it may require inspection to find out what is going on. It appears this would require pulling the head(s) to inspect the lifters/cam?

rwd

I'm glad to hear the dealer agreed there was an issue. It keeps your options open.

Hopefully, what you can learn with a stethoscope or rod (or screwdriver) will be revealing. If you can't find a steth, don't worry, you really don't need one. Any rigid rod will work, and non-conductive is preferred, of course. For that matter, a yardstick might even work. No need to get too close to your work, and the volume will be more than sufficient.

It's difficult to quantify loud, normal and black. Mine has no repetitive tapping sounds. Inside the exhaust (the exterior can be contaminated), mine has a fine coating of light gray soot, and that should be about right. I had to rub a second time to get some off; the first time, my finger was still clean. Black would concern me a bit.

I'm not expert, but my guess would be the lifters would be more at risk than anything else during normal operation. In extreme cases the bottom end might suffer, and bubbles might show up on a dipstick, but that'd be extreme. There's no reason to think that's the case, but you're right, it's not a good situation.

It's just as likely to be something simple. I suppose a short pushrod might do that (or perhaps the lash adjustment). It could also be a small piece of debris left over from the build that's plugged something, or just a bad lifter. It may not be an aeration issue.

There's no reason I'm aware of to expect any damage to the cam, pushrods or bottom end, and the increased noise might simply be the lifter further collapsing.

I haven't gotten the manuals yet, but I'd expect the lifter/cam area to be accessed by taking the intake manifold off. In any case, sorry you're having problems, and good luck.

johnC5

No only did they agree there was an issue, they offered to do the TSB. Unfortunately, they also said it would not fix the problem: just document and wait for a known fix or wait for a bigger issue to arise.

I borrwed a stethoscope with a metal probe: quite loud(!) when placed on various parts. I probed all around the valve covers: I could not locate any specific variance in sound.

What is really strange is the sound really is the loudest from underneath the car. Doesn't necessarily mean the sound is coming from there, it just appears to propagate there (I could hear clicking noise with the steth on the oil pan).

Here's another clue: after the car has been allowed to sit for a while (30+ minutes) after warming up to 200+ oil temp, the car can be started with no major ticking. If the car is then revved to about 3000 RPM for a few seconds, after returning to idle the ticking sound is quite loud, and it keeps on ticking.


[Modified by johnC5, 4:16 PM 2/21/2003]