2006 i6 Upper engine noise, now have the head open

bac217

Original poster
Member
Jul 26, 2021
8
Utah
Hello, new here... I was given a trailblazer to turn into an off-road rig and finally got it home to get it workin. Details:

2006 Trailblazer LS
i6 4200 Vortec
4WD
(not sure what else is helpful?)

It was parked in early 2020 due to engine noise and no power. My father in law suspects it is a plugged catalytic converter but I'm not sure on that.

Here is a video of it running before I opened up the head. What I was hearing seemed to be a bit more random than just with Engine RPM's. Definitely in the top of the engine, and I believe back in Cylinder 5/6 area of the head.



However, I've since gotten the valve cover off and my initial suspicion of issues with the valves/rollers/etc. seems to be fine. The rockers are tight on all of them except some wiggle ever so slightly. I suspect this is just due to cam position, agreed?

Now, my biggest question is "is this timing chain too loose"?


Or is that normal play in a timing chain?

The PCV tube sure barfed oil all over the top of the valve cover... I hear this can cause some uglyness with these Atlas engines

20210802_172224.jpg

I also suspect the VVT Solenoid may be having issues. I've previously seen one way to check the health of it quick is "is the electrical connector full of oil?" and no, mine is dry.

I plan to take the VVT solenoid off today if I can and test/clean it.
 

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rchalmers3

Member
Jul 11, 2020
207
Irmo, SC
Hiya bac217, welcome to the forum!

Before chasing and testing/replacing components, I suggest you perform an engine oil pressure test. These engines have some trouble with the rod bearings, and while I'm not suggesting that is the noise, I am urging you to confirm the health of the engine before going after other repairs. You will find some excellent threads on this forum for measuring the oil pressure utilizing an external mechanical gauge. The dash gauge is not an accurate devise. Some say it lies.

The timing chain looks acceptable. You are accessing the slack side of the chain while the oil pressure is at zero, so I'm not surprised to see a little play.

Let us know the results of the oil pressure test, then we can plot a course of actions that will lead you to success with this case.

Cheers,
Rick
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Does the knocking noise go away above idle? Can you feel it on the valve cover next to the oil filler or hear it from the oil filler? If so, it's the chain tensioner. Sure sounds like it to me. Been there, done that. Not a fun job to replace it. You can use it as-is as an off road rig as the tensioner's ratcheting mechanism has failed however the oil pressure portion of it will work to tighten the chain at higher pressure. At lower pressure, it's the ratcheting part that's supposed to hold the tension.

And if you're wondering about replacing the tensioner:

How to replace I6 timing chain and tensioner

Like I said, not fun.
 

bac217

Original poster
Member
Jul 26, 2021
8
Utah
It was super bogged down when revving. It threw a Code that I wish I could remember, I'll do some digging and let you know if I can find the actual Code but I am quite certain it was Cylinder 5 misfire.

If I tried to rev it, it got more pist off and wouldn't go above like ~1200 RPM. So its possible that the tensioner may be loose and as you said 'can use as is' but also has a more serious misfire in addition? I believe I recall it blinking the check engine light.

Before I took it apart I swapped Cylinder 5 and 6 coils and it didn't change anything from what I recall. Hard to say without bein able to go out and fire it up anymore :-X .

Thanks for the article, I've been lurkin for a while but haven't posted till I got it home to where I can actually work on it lol. I've read through the process of just about everything just to soak in what I can about the Atlas.

Does that video of the timing chain's play look excessive? Does that movement even say anything lol
 

c good

Member
Dec 8, 2011
526
How many miles? I would get a good automotive stethoscope. If you can isolate the sound to the front of the engine then probably a timing chain tensioner as others have mentioned. If it's towards the rear or middle of the engine....that could be a rod knock. There's definitely some piston slap going on but you can live with that.
 

bac217

Original poster
Member
Jul 26, 2021
8
Utah
~238k miles . Edit: I think? Sounds high now that I'm re-reading that but 138k sounds low. I remember 38k @ the end lol

So, should I re-assemble it up and put the valve cover / intake back on and try firing it back up?

I had a Rod Knock in my camaro back in the day, and I ended up blowin it up lol. But That had a very distinct slower sound @ Engine RPM. When I see youtube's of rod knock I immediately go "YEP that's the sound my camaro did!" , I'm not hear in that blatant telltale of a rod knock here. (knock on wood). It seemed more random like it went with RPM's, but then would rattle a bit. I'm now envisioning that I could totally see a loose chain slappin around cause what it sounded like to me.

I suspect its got a junk belt tensioner too, I couldn't get it to budge so took the 3 alternator bolts off with the belt on then that slipped it out :wowfaint:
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
I'd do a compression test on all the cylinders with the cover off so you can see and hear any noises. The misfire could be something as simple as a bad coil.

For the engine to be rev limited like that, I would think it went into reduced power mode. The exact codes would help here. If the compression test is good, I'd put it all back together and try to get it to give the code again.
 

bac217

Original poster
Member
Jul 26, 2021
8
Utah
I went and pulled the VVT solenoid and cleaned it up. It is actuating nicely but it had a little bit of metal shavings on the screens of it :hopeless:

How should I go about doin compression with the valve cover / intake off. Just crank it as usual? I just ask because I've only ever done compression tests to intact engines before lol
 
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mrrsm

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Oct 22, 2015
7,641
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Welcome to GMT Nation...

A Few Observations...

(1) ASAP...Get a Can of "Kroil...The Oil That Creeps" and LIBERALLY Spray down your Camshaft Lobes and Roller Followers ... otherwise, during the first Damp or Rainy Day, all of those Camshaft Lobes will completely Rust Up.

(2) Based upon the lack of Heavy Black Carbon in the Top End and that "Fried Chicken Brown to Honey Golden" color on everything, THAT Engine seems to have been very well treated and It looks like Oil Starvation has NOT been the problem... so far.

(3) I'm hearing sounds that make me think they might be coming from the extreme ends of the Engine Block ...such as either the Water Pump Block Cavity ...or perhaps from having a Cracked Flywheel.

(4) If you decide Button Up the Motor... Take a Video that divides time between the Top, then BOTH sides of the Fender Wells and under the areas adjacent the Bell Housing to Block areas as the engine is Idling ....hovering with a Steady Camera at each station to help isolate the sounds and Post it back here.

(5) If the Timing Chain Guides and Tensioner were completely worn out or collapsed... you would be able to wobble the Cam Phaser Exhaust Camshaft Sprocket and Chain around a Whole LOT more.
 
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bac217

Original poster
Member
Jul 26, 2021
8
Utah
I was thinking that too @ rust on exposed parts, so for the time being I haven't torqued down the bolts but I did put the valve cover back on it. Hopefully that sufficient for now but yeah I should get oil too..

That's good @ oil coloring, I figured the inside of the oil cover would be a useful picture for forensics. Thanks for the input on that.

I've seen some cracked/warped flywheel stuff out there that seemed similar to this, have been crossing my fingers it's not that but it may be :Banghead:

Whenever applicable I'll make sure to get a better video around everywhere too.
 
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mrrsm

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You should be hoping that a Cracked Flywheel IS defintively the problem as it will bode well for the survival of that Plucky Atlas Engine; albeit, while making for an awful lot of additional labor to sort things out. One last thing to mention is checking the Harmonic Balancer and Crankshaft Bolt... Pull the Serpentine Belt and see if you can move around or fore and aft ...even a smidgen by hand....and then Start the Engine at idle as THAT will allow you the chance to eliminate the Water Pump as the cause of the noise from the equation. Don't let the motor run like this for more than a minute... ...and have your Camera "at the ready...".
 
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bac217

Original poster
Member
Jul 26, 2021
8
Utah
@rchalmers3 I'll check into oil pressure and read into all that.

My father in law has the compression gauges to check cylinder compression so I can hopefully do that shortly but I'll see what all I need to do the oil check. I'm decently set on the knowledge but limited on tools hah. I love that it's a 2006 as I went to college for the General Motors ASEP/BSEP program in 2006. I've rebuilt the 3.7 altlas based engine, 4L60E, 4T60, Allison, etc.

It's nice to see a laptop OBDII adaptor with full Tech 2 capabilities is managably priced these days haha
 
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bac217

Original poster
Member
Jul 26, 2021
8
Utah
Still workin on gettin the compression tester, I'ma just end up renting them. There was supposed to have been one I could use but it ended up getting packed in a move. I haven't had great luck with rental tools is why I haven't just done that yet either.

But I'll be cleaning the Injectors , compression testing, then re-assembling the engine here shortly.

I'll check out exhaust stuff, my father in law who gave me it initially thought it was a plugged Cat.
 
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rchalmers3

Member
Jul 11, 2020
207
Irmo, SC
Thanks for the report and let us know what you find.

As per my original post #2, I suggest you get a baseline reading on oil pressure.

Rick
 

bac217

Original poster
Member
Jul 26, 2021
8
Utah
This is going to be a slow "as I get the funds / as I get the time" kinda project... But I agree I gotta check out oil pressure. Not sure how to go about doing that but I'll get researching what is needed and what to hook up.

Currently the battery is charging to do the compression test engine turn-over.

I made an adaptor to pressurize up a section of 1/2" tubing with a can of carb cleaner and then 12v on a button to pulse the fuel injector to blast em all clean and confirm the solenoid does its thing nicely.
 

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mrrsm

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