olddragger

Before I start just let me say I have read every findable entry concerning LS7 engine noise that I could find. I don't like cluttering up the forum with the same questions asked repeatedly.
My car is stock--73000 miles , heads redone by AHP, they were milled 0.020 and I am using 7.75 push rods as advised. new set of oem springs and new oem lifters. The cam lobes looked ok when I did the heads. This all was done on December 2015. I have maybe 3K miles on them.
About 2 months ago the engine developed a ticking/clacking ONLY ON DECELERATON between the rpms of 2500---1500. It is clearly audible more so inside the car than outside. It is coming from the passenger side. I listen with a stethoscope and I really couldn't hear anything that was suspicious anywhere. I was surprised at the noise of the injectors though. Now my engine has the common sewing machine sound ---but it is not bad. I have carefully listened for any abnormal noise during cruising and acceleration ---but couldn't not hear anything abnormal.
This DECELERATION ticking /clacking is present cold/or hot, it does seem to lessen after a fairly hard running through a couple of gears gears.
Ok --I took the valve covers off, rockers look good. I removed the push rods---nothing is jumping at me. I look down to the lifters as well as you can and see nothing. I replace the push rods and test for any soft lifters---nope---nothing gave. I button it all back together. Hmm?
Ok --high mile engine--so I try a 20w/50 oil---just for the hell of it.
That did change the tone of the tapping/clacking somewhat- but it did not alleviate the noise. I ran it for about 100 miles and took it out and replaced with moble 1w 0/40 . I am running the mobile 1 oil filter. Oil
pressure is great---cold start=about 80, hot idle at 650rpms is 25-28.
I have been under the car and there is no exhaust leak. The water pump, tensioner, alternator all sound good with the stethoscope.
Again --willing to try anything--I put seafoam in the oil as recommended---DAMN--seemed to actually help a little! I drove very lightly ( rpms and load) for about 25 miles and changed oil again. Its better but it does remain. Strange to say some days are worst than others Did gunk get into a lifter after head install? I don't have a clue. if it did then why just on decal during that rpm span?

WHAT the heck is this noise? I don't want to chase my tail , but I like for everything to be solid as possible. I do not want to remove the heads unless I have too, hence my reaching out to the forum too those wiser and smarter than myself.
I repeat this is ONLY DURING DECELERATION BETWEEN RPMS OF 2500--1500. Once those rpms points are crossed it goes away.
Just to add, compression is good on all cylinders and no codes of any type.

Landru

Whatever it is it may be a warning. Now.
Your ears aren't lying so something's certainly amiss.

Given what these engines cost removing/inspecting heads ASAP may be the wisest next move. G/L

MTPZ06

I see you've inspected thoroughly, and I was going to suggest lifters...but heck; they're cheap enough maybe just replace them anyways?

olddragger

Maybe I got a bad lifter in the set then? There is only about 3K miles on this set.
Pulling heads in my garage is not fun and was hoping for some miracle knowledge by some zo6 shaman.
Why oh why do I have a feeling I am going to end up going through this motor because of this ticking?? That really will not be the Christmas present i was hoping for.
I think I may park it and start riding my bicycle again. Never mind that there is something pitiful about a gray haired 67 yr old man riding a bike to work.

C5 Hardtop

My '08 had the sewing machine noise at 400 mi. It blew at 35k mi. I hear the sewing machine noise is indicative of the valve train problem where the valve guides wear out. Yes, I know you have had the heads done and whatever. I'm just saying what my experience is.

outhouse

Use your scope and investigate the oring problem known to sometimes come from inside the sump.


Just an idea.

outhouse

Kohle states that is more of a metallic knock, more so then the regular everyday valve train noise.


My engine before I tore it down had a loud lifter noise over 2000k, but all lifters were in perfect shape and the cam.


Now with all new valavetrain and different cam I get idle to 1500 tapping sound and with dual springs that sewing machine is really alive lol


They are just noisy engines. as you know

C5 Hardtop

Back in the day, LS7's were blowing at a rate that the LS1's and LS6's were not. On or off track, it didn't matter. Driving at 30 MPH or on the freeway at cruising speed. It was abnormal and the forum was all over it. Nobody knew what the deal was.

In '12, my engine blew. It was under warranty and 1 month later for the repairs, I got the car back. The gm regional engineer gave me the low down which I posted here. That post opened a can of worms. Connected people here backed up the findings with their own investigation. Katech had egg all over their face. Within these findings was another GM engineer who coined the term sowing machine and associated it with the problematic valve train problem.

outhouse

These loud valve trains also give people trouble because when they do have a real problem, it is easy to blame the problem as a normal noise when its not.


Its a shame the heads all don't have the window ground in the heads so lifter can be removed without removing heads to investigate without a major tear down.

C5 Hardtop

Its a shame the valve train problem exists in the first place.

08mojo

This is a good place to start OP. From the symptoms you list, it certainly reminds me of the stories I read about the oring cracking in the dry sump. Do a search for those threads and see if the descriptions match what you are hearing.

As for the sewing machine noise, that is normal. My car made the sewing machine noise when I bought it and made the same noises when the I rebuilt the entire top end.

MTPZ06

Certainly plausible. Here's the info on that o ring:

08-06-01-019: Rattle/Tapping Type Noise Heard Under Hood (Diagnose and Replace Engine Oil Tank Transfer Tube Seal (O-Ring)) - (Aug 13, 2008)


Subject: Rattle/Tapping Type Noise Heard Under Hood (Diagnose and Replace Engine Oil Tank Transfer Tube Seal (O-Ring))


Models: 2006-2009 Chevrolet Corvette Z06

2009 Chevrolet Corvette ZR1 with 6.2L or 7.0L Engine (VINs R, E -- RPOs LS9, LS7)

Condition

Some customers may comment on a rattle or tapping type noise that is heard under the hood at just above idle, usually 1200 to 2200 RPM. In some cases, this noise may also be heard on the inside of the vehicle and be more pronounced on the passenger side.

Cause

This noise may be caused by the internal transfer tube in the engine oil tank hitting the inside of the tank cover. The seal (o-ring) that secures the tube in place may split and slide down the tube allowing the tube to be loose.

Correction

Diagnose the noise by raising the vehicle on a hoist and holding the throttle at about 1500 RPM to duplicate the condition.
Use a stethoscope or chassis ears and place them on the side of the engine oil tank. If the noise is detected, perform the procedure outlined below. If the noise is not detected, continue following published diagnostics in SI.

Remove the engine oil tank from the vehicle. Refer to the Oil Tank Replacement procedure in SI.

Remove the eight bolts that secure the tank top.

Separate the tank. Check the seal (o-ring) for proper position and damage. Replace the seal (o-ring) if damaged with P/N 24576940.

Reinstall the tank top and secure with the eight bolts.
Install the engine oil tank into the vehicle.
Refer to the Oil Tank Replacement procedure in SI.

Parts Information
Part Number ---------------- Description ---------------- Qty

24576940 Seal (O-Ring), Engine Oil (Tank Transfer Tube) 1

olddragger

Thanks all, I thought about the oil tank o ring, but since this is only on deceleration I didn't think that would be it. Still it's an easy look at and sure better than pulling the heads.
I think I will give that a shot. Maybe karma will be kind.
But for now it's parked ..... Sad.
Hopefully will have time this weekend.
When I listened to the tank at idle it was quiet. Didn't have a helper at the time.

Dan_the_C5_Man

If you need help with the diagnosis, let me know.

olddragger

Thanks Dan
I was wishing for that sweet lift of yours as I was jacking mine up and placing stands this past weekend. Lol
Wouldn't you know, it hasn't rained in 35 or so days here in Atlanta , but the day I park my car and was going to ride my Prodeco e bike to work,
It rains.
What really throws me about this sound is that it is only there during deceleration. That characteristic is why I am thinking that it is not a lifter. Lifters have a constant load on them. It varies to the rpm...true, but aceleration/decel doesnt matter. If a lifter noise is present at a certain rpm , then it should be the same while you are acelerating during that rpm also?
It doesn't matter if I have the clutch in or out during the decel either, although it is much more audible if the clutch is in and the engine is decelerating at a faster rate.
By the way, the engine is very clean. When I drained the oil after the sea foam ..treatment..it was as clear as when I put it in.
One thing I have discovered.... It's louder with the fuel rail covers on. I think the covers help direct the sound toward the cabin.
This is turning into a quest.

meanjoe

Do you have a way to record this noise and post it on here? The other thing I would suggest, even though you sound like a die hard DIY'er, before you start tearing things apart would be too take it to a good LS shop in your area and have them take a listen.

olddragger

meanjoe---if a smart phone will capture it I certainly will try.
Yes I agree at times consultation is pertinent---but you did sum me up right! Strong desire to DIY things. Sometimes the journey is worth it. Sometimes it is not. In this case
if I don't find something soon, you are right-- it is time to go to plan B.

olddragger

Ok I piddled with this last evening for a few mins. Pulled the passenger side valve cover and a few rocker arms. I noticed something I didn't before? How can you tell if the rocker arm cup is worn out? Perhaps mine are worn to the point of replacement?
How much rocker arm side to side movement is ok? Bearings are intact.
Also noticed that the rocker arm sweep pattern is a little off center. It is nice and square but it is bigger than it was before the head work. Pattern on the valve tip looks good. So question concerning the sweep pattern being off center of the rocker arm... Does that really matter?
Stock cam and springs.
My heads were milled 0.020 and I was told to run 7.75 push rods. Getting good oil supply to the top end

I had a helper and I listened to the oil tank.with stethoscope ....no unusual noise. Just oil flow sounds. Nothing metallic.

08mojo

Can you post a picture? Might not be a bad idea to pull all the rocker arms and compare the cups--although I doubt this is your issue. I'd make sure none of the stock needle bearings are missing from the rockers. Other than that, I'm a bit baffled by what could be causing the noise.

MTPZ06

I still go back to this. The issue didn't appear until after your build, so it is plausible that after 3K miles a "bad" or suspect lifter is beginning to degrade. Swap them out...not a lot of money. Time consuming yes, but its worthy of your time IMO. Aside from this, I too am running out of ideas.