I'm got a very unique chirping noise coming from the rear of my engine bay -- I'm looking to get some insight on what you might think it is.

A little history:
Two nights ago I met up with a friend (I'm back home for break from College) and we went out just to cruise around town. We got on an open stretch of highway and he wanted to see how the car felt on the bottle. So I opened the bottle and sprayed it at about 3600rpms from a 60 roll. The car backfired and sputtered pretty hard so I let off pretty quickly. I purged and tried one more time and the same result. It was behaving similarly to when I was getting some spark blowout, so yesterday I decided to pull the plugs and see how they looked. This is basically what I found.




There was a little green on the top, which I know is from the nitrous. The white is what really concerned me. I haven't had the car dynoed on the spray , but I've always run the kit a little on the low side of nitrous pressure (~980ish) just to be safe with the wet kit, I know that NX jets their kits a little rich anyways. I did seafoam my car (all three steps) about two weeks ago, so that would probably explain the white on the plugs.

So I replace all the plugs and gap then at .033 and start the car back up. Pretty much right after it starts back up, I'm hearing a chirping. I popped the hood and looked and it sounded like it was coming from the rear of the engine bay. I know the acoustics inside a garage with the engine bay can trick you, but it definately seems to be coming from the back. I was hoping it'd be a quick easy fix and I sprayed a some silicone lubricant on the tensioner pulley, but to no avail its still making the noise. It seems to speed up with the rpms, but it isn't constant when the engine slows back down.

Here is a quick vid (apologies for low quality) of the chirping and a slight rev. Any one who has had this happen, or can explain it. I'd really appreciate it.



Some background info so you don't have to ask:
Its a '94 Z28 Automatic. I've got the LT4 Hot Cam kit with the basic supporting bolt-ons. The plugs are NGK TR6s gapped at .033. The serpentine belt has less than 5,000 miles on it. The car still drives, but with it sounding like its kind of coming from the passenger valve cover, I'm parking it until I can get it figured out.

 

Man, that almost sounds like a roller rocker is coming apart. Pull those valve covers, start it for a few seconds and see if that noise is any louder. Do one at a time and see what side it is coming from.

If anything, get out your timing light and put it on individual cylinders to see which one is making the noise.....just to narrow it down. kinda hard to do, but I have done it once or twice to find where an exhaust leak was coming from.

What about your opti? Is there any chance it might be making the noise?

Just throwing out ideas. I know how hard it is finding a grimlin.

Joe

 

Thanks for the response. Joe's stick together

I went ahead and pulled both valve covers. I pulled off all of the rockers and checked all of the pushrods (on a hunch it could be a bent pushrod). If any of the pushrods are in fact bent, it is extremely minimal. I'm going to put in a new set of OE rods tomorrow while I've got everything apart (still rocking the 78,000 mile stockers).

Once I've got the valve lash adjusted with the new pushrods, I'm going to start it up real quick with the covers off to see if the sound is still there. I've got a hunch that it is going to clear it up.

From the people I've talked to, they said it sounds like a bent pushrod, or the sputter/backfire might have tweaked the valve lash that was off a little bit, and now its off just enough to screw with things.

Before I took the valve covers off, it was running fine. At WOT it doesn't skip at beat, but at idle it does falter a little bit (more than usual with the cam). Worse comes to worse I'm going to do a compression test if it is still making the noise (worse case scenario).

If anyone else has any input I'd greatly appreciate it.

 

I got a chance to put the pushrods on the kitchen counter and roll them around, there were three of them that didn't roll constantly -- showing evidence of being slightly bent. Not hardly noticeable if you just hold it up and look at it though. I'm hoping that this was the culprit.

With the new pushrods and adjusting the valves -- the chirping is gone. However it is definately running rough, so I'm going to have to go back and readjust the rockers again. I followed ShBox's writeup, so I'm really not too sure what I did wrong.

Basically I put a breaker bar on the crank pulley and turned it clockwise while watching the rockers. When the pushrod went all the way down (assuming the valve is closed) I tightened the rocker nut while spinning the pushrod. As soon as the pushrod stopped spinning. I turned the nut another 1/2 turn and held it tight while I tightened the poly lock (fairly hard).

There is an intermittent tick (doesn't go at any sort of rhythm like the chirp did) that I personally feel is more related to the valves not being adjusted correctly than the previous problem.

I took vid of it right after I cranked it up -- input on whether you think it sounds too tight or too loose? I know that's hard to tell on a lower quality video, but any other input would be appreciated. Thanks again for the help thus far guys, I really appreciate it.

 

Did you check to make sure that all the rocker arms where getting oil before putting the valve covers back on? If not you should take the valve covers off and check to make sure they are all getting oil.

 

That I did not do. I did crank the engine a couple times with the coil wire unplugged to get some oil pressure before I started it. I'm going to take the valve covers back off tomorrow and re-adjust the valves. I think I realize what I did wrong the first time adjusted them, so this should fix it.

 

LT1, you do have a point, if one of the rocker arms were not getting oil, the rocker might be making the squeeeeeking sound.

Joe

 

Update (for those who care)

I put in 16 new pushrods (after finding three of the factory 80k mile pushrods were slightly warped). I readjusted the rockers with the correct pre-load, and insured that all of the rockers were getting oil. I assumed the chirping was being caused by the slightly bent pushrods, but when I cranked the car back up it was still making noise.

I tossed around the idea that it could be a possible blown header gasket. So I pulled off both headers and checked the gaskets, they look old(er), but definately not blown. If I end up having to tear into anything more hardcore, I'll probably end up replacing them.

I noticed the passenger side header had 4 of the 6 bolts extremely loose when I was taking it off to check the gasket, when I retorqued them down when I put it back together.

The chirp still remains

I didn't get a chance to get a compression tester, but I'm going to do that the day after christmas (hoping for a sale). I'll probably pick up an automotive stethescope as well.

At this point, I am sincerely stumped. I can't really think of what it can be now. Is there still a possibility it could be a lifter or broken/burnt valve? The car still idles and runs fine, it just chirps. I'm running it off of the battery (no serpentine belt, alternator removed) and the chirp still remains.



Thanks again for all of the input guys, I wish you all a very happy holiday

 

Have you checked the side to side movement of the rocker arms? I had a buddy adjust his wrong and it bent one of the pushrods. We just happened to have a new pushrod at the track and I put it in and he adjusted it while I went to make a pass. It still made a ticking noise so we took the valve cover back off and he didn't have it adjusted right. It was too loose and I could move it side to side. I tightened it correctly and it quit ticking.


Just tossing ideas out, could it be the timing chain?

 

The rocker arms are properly adjusted. When I replaced the pushrods (assuming that was the issue) I was sure (and double checked) the rocker adjustment at zero lash with the proper preload.

I scoped the car yesterday and found that the chirp is definately coming from the rear of the passenger valve cover.

With the compression test that I did today, I really didn't find anything too conclusive. The numbers seemed within normal tolerances throughout the cylinders.

Would you think this is leaning towards a possible lifter?

 

After the results of the compression test -- I'm leaning more towards a lifter being the issue and not a valve.

After doing some searching, a lot of people say that the Comp OE Replacement Lifters are more than apt to get the job done. I was considering forking the money over for some Morels, but with only the hot cam and springs I have a hard time justifying it.

Just to double check, the 850's are the Comp OE Replacements correct?
http://store.summitracing.com/partde...5&autoview=sku

Also -- I know I'll need an intake manifold gasket set. Is there anything else I need to know before tackling the install? Does anyone know of a writeup on it?

One last thing -- is this Comp Hydraulic Lifter Install Kit suggested as part of the install?
http://store.summitracing.com/partde...rt=CCA-08-1000

 

I am thinking a collapsed lifter(s) could be the culprit. The sound is very similar to other vehicles I have heard with that problem. In fact, a buddies 302 SBF was making the same sound as you describe and ended up with 13 collapsed lifters, bent rods, and a flattened cam. Pull the lifters out and see if any are collapsed. I would replace them one way or the other, never hurts.

Keep us up to date on your progress.

 

I had the same problem on my LT1 Z-28. It turned out that the rocker arm oil pivet sleave in the rocker arm stopped moving. if it stoppes moving its gonna squeek really bad. That could be the cuplret of running lean with nitrous. Those plugs are very lean. Trust me. I learned my lesson. If you run that lean cylinder temps can go up to 1000 degrees. Double check your O2's. If you have a 95 model then it is a generic year. It will not throw a code for O2 sensors going bad. If it did go bad then the squeeking is the lean condition your motor is making because it cannot read the exhaust gasses passing through that bank. Sorry to say but if thats the case ...... thats just your rings making all of that noise. Nitrous backfire through the exhause can and will very easly fry an O2.

 

When I pulled off all of the rockers and checked them by hand, they all looked fine. The pivot area rotated freely and they are definitely getting oil.

The new set of plugs (driving N/A for a day before I put the car up on jackstands) are definitely lean. I'm in desperate need of a new tune. Looks like my mailorder tune just isn't cutting it.

During the compression test, the car built pressure each compression stroke, it didn't bleed down at all, or stay stead during multiple compression strokes. All of the cylinders also were between 180 and 210 psi. This is what leads me to believe the chirp is more of a lifter issue than a ring or valve. I will check my O2s -- but before I put the car on stands it was running fine in closed loop.

 

Quick update on my progress.

The car has been sitting since I ordered the new GMPP Lifter Kit and Gaskets. I decided to be proactive and actually pass the time (sucks without having a car) by doing something somewhat useful until the parts got here.

So the lifters came in the mail today -- so I've got them soaking. I'm going to try to get everything installed and start buttoning it back up tonite.

I decided to join the 'Rattle-Can Brigade' and paint a little bit on my intake manifold. I also did my best to do a thorough cleaning of everything while I've got it apart.

Here is the motor as it sits now. I haven't pulled the lifters yet, I'm going to tackle that after dinner.



Here is the intake off the car and throttle body before:



And here is the intake and throttle body after:



A close up of my red hot painting skills:


And decided I might as well throw on the EGR blockoff plates while I've got the intake off completely:

 

Sounds like a spun connecting rod bearing. How high did you rev it?

 

I've never revved the car over 6200 rpms.

Spun bearing?

I was under the impression a spun bearing sounded more like marbles or a garbling sound in the intake. This is most definately a chirping sound.

 

So I got all of the lifters back in, all of the guides and guide retainer (spider) back on. The guideplates for the pushrods are back on as well. When I was putting the rockers back on -- I found something. I'm thinking this might be the culprit. Opinions?

 

I was having noise from the rear passenger side that I was intending on readjusting to zero lash. At this point, I think that it is possible.

So now, I did some googling on GM 1.6 Roller Rockers (because I've got the LT4 Hotcam Kit). There was a recall on the roller rockers on the '96 LT4 Vettes and they replaced them with GM Part # 12557779. Which is actually individually priced 1.6 Roller Rockers.

Does anyone see why this wouldn't work with mine?

 

I would think it would work with you car just fine
and if it was a spun bearing trust me you would know....

also how dose the car run on the N2O