Timbrooks720

Ok so I have developed a new clacking/knock sound while i was cruising at about 70 on the freeway. It started out very subtle and made what sounded to me like a bad lifter or bent pushrod and then got progressively LOUDER!

So now, when the car is cold, it's quiet (except the normal cold knock that it's had forever like every other LS powered vehicle) and doesn't make much noise through all RPMs.

When the engine is at running temperature, it is quiet under load and acceleration, quiet under deceleration, quiet at idle. It is NOISEY as HELL when im cruising at around 1500 to 2100 rpm. So if im in 1st gear in traffic at 1500-2100 rpm is LOUD as HELL. Same with 2nd, 3rd and so on. If i gun it though the gears its quiet. Torque converter bolts? Help before i blow money on an engine!

Yes it has oil.

lucky131969

If this is really your concern, stop driving the car until you find the source...

Can you reproduce the knock at the same RPM with the car stationary? Can you isolate the knock to a certain location on the car?

Timbrooks720

Yes I can make the sound occur while in park. Same deal with the RPM range. I used a stethoscope and poked around and found nothing. Only hint of sound I got was off the water pump housing which doesnt really make sense to me.

dgrant3830

So, its happening at a specific RPM range... not at idle and not under load...rattling? I'm not an engine expert by any means but I tend to worry that this sounds like a rod just starting to go bad. I could be way wrong too, so please someone with better engine knowledge chime in and suggest something less serious. In the mean time, I suggest you drain the oil and look for metal. Also, cut open the oil filter and check for metal particles.

lucky131969

Ok, so it sounds like you are half way there. If you can reproduce the noise in park, but can't isolate it to a location, how do you expect anyone to help you?

Timbrooks720

Wow.. Harsh. Well...

A I am not a mechanic.
B It just started happening.
C I don't have access to a lift or autoshop.
D I'm not expecting much since I'm not paying anyone here to diagnose my car. I'm just in a bind and would help you guys out if you had some kind of photoshop problem or couldn't get the head spacing right on your AR-15.

The noise is a one per revolution kind of sound.. It speeds up and slows down with the rpm.

Timbrooks720

I'm about to rip the serp belt off on my lunch break to see if it still does it. I'll update. The stethoscope was loudest on the water pump housing. Not on the valve cover, not on the exhaust, head, etc.

lucky131969

Harsh....ok, here we go....putting on kid gloves.

I understand your dilemma, but we need more info as to the origin of the knock. If the knock can be isolated to a part of the car i.e. rear end, center, engine compartment.....then we can take some educated guesses as to the origin. The fact that it can be reproduced with the car stationary at least counts out the wheels(and parts associated with their motion). Perhaps you can get the help of a local forum member if you disclose your location.

Timbrooks720

OK so took belt off, still the same. I noticed the balancer/pulley combo wobbles but is not loose. Has anyone seen one of these go bad? Would the AC pump make a similar sound when going south? Being engaged and not engaged yeilds same sound. I'm in Long Beach, Ca. Need to fill out my profile

lucky131969

There are dozens of threads on the balancer wobble. It really depends on how bad it is before it requires replacement. They all seem to have a little movement, but it should not be excessive. Could the A/C pump knock? Guess it now determines what you are calling a knock v/s a chatter, etc.

Anyone is the Long Beach area that can lend a second set of ears/eyes to help the OP out?

Timbrooks720

OMG what's OP? That mean i am Over Powered? I hope it's not Old Pedophile.

So the sound is like a ball peen hammer tapping an anvil.

lucky131969

OP= original poster i.e....you. I can't walk on eggshells here.....I'll leave this to our more sensitive forum members.

Good luck

Timbrooks720

lol I just asked what OP meant. Sorry, I'm not fluent in forum jargon.

Chevy-SS

LOL, "OP" means "original poster". I've been thinking about getting an AR-15, so I might have a question or two for ya at some point, but I digress.....

I think you have provided a good bit of info. The noise:
1) appears directly related to engine rpm
2) happens while vehicle is still
3) happens with belt off

Therefore, I am thinking it's something internal to the engine. My 'guess' would be a bad lifter that is allowing itself to bleed down when hot, but when cold it holds oil and thus there is no noise. A hydraulic lifter bore fitment is incredibly precise, so the tiniest bit of leakdown could cause a clacking lifter. The noise can get very loud.

Here's how I would check it (the do-it-yourself method - DIY). Warm the engine up thoroughly, then take off the valve covers. Make sure to prep adequately, so that the engine is still hot (and the noise is readily apparent) when the valve covers are removed. Then wiggle each rocker (all 16) with your fingers. If all appear tight, rotate the engine one full turn, then test again. You should find one that's loose if it's a bad/collapsed lifter.

If it was a bad rod bearing, it would be more of a deep banging or throbbing. The cold-start 'piston slap' you hear is caused by one (or more) of your pistons being slightly too loose in the bore. But the pistons expand as the engine warms, and thus the piston slap goes away. This piston slap is a typical problem in many performance engines.

Hope this helps.

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Timbrooks720

Yeah I thought about tearing the valve cover off and spinning a few rods this weekend as long as it stops raining! It hasn't lost any power, idles as smooth as Sophia Vergeras backside, and doesn't overheat. Also, the oil is clean (Mobil 1) with no sparkles or anything out of the ordinary.

Build an AR-15! If you can screw in a light bulb, you can make an AR-15. I'll post some pics of my beast.

Chevy-SS

If you can run the engine with valve covers off, then you should be able to find the bad one very quickly! I just take a rag and press down on each rocker, the noise will pretty much stop right then.

I am an old-school Chevy guy. Done lots of big-blocks and small-blocks, but never even had the valve covers off on a LSX engine, lol.......


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Timbrooks720

Sounds dangerous. Danger is my middle name. Well... after cecil. Don't tell anyone that. Oops i just did.

kvadnais

FYI... I'm located in Santa Ana (20min from Long Beach), and I'm currently dealing with a very similar noise on my '02 Z06. However it's a little more similar to trashed rod bearing. Somewhat of a RPM-based knocking sound, lower in the engine/bay (almost bell-housing region).

I'z getting on freeway when the noise started, immediately threw into neutral, coasted to next off-ramp, and towed the car home. The next day I started it again, same noise, but this time it was noticably louder. All the while, no fault/error codes were reported on the computer, and I had plenty of oil pressure (40psi+).

Did the basic troubleshooting steps:

1) Drained the oil, cut the filter in half. Nothing out of line. Very clean fresh looking oil, filter didn't have debris in it.

2) Pulled the valve covers, checked the springs, pushrods, etc. Couldn't find anything to substantiate the noise/sound.

3) Pulled the plugs, did a leak down test. All cylinders were well-within each others average.

4) Pulled the "rear/lower" oil pan, which was almost useless, but no visible evidence of something nasty taking place (metal shavings, etc). So unless it's simply a broken rod bolt, I can't understand why I'm not finding copper looking material so far (in the drained oil, filter, rear-pan, etc).

5) I'd love to take the entire oil pan off, except... (and this still baffles me) ...we can't take the pans off these cars without dropping the sub-frame/cradle, or pull the motor itself out. I have a lift at my house, so I'm doing all this with it 6ft in the air. If I remove the cradle, how do I support the engine while the cradle is removed?

At this rate, I'm suspecting pulling the motor is the path of least resistance.

Timbrooks720

I found this on youtube. Very similar sound....

http://www.youtube.com/watch?v=gRSrUQudaP0

Dragon Daddy

Try going here:

http://corvettemechanic.com/forum/

and asking the c4c5specialist.