2007 Trailblazer LS engine noise (sounds like rattling then it makes a clang)!

[phogstenjr]

Hello,

I purchased a 2007 Trailblazer LS with the 4.2L I-6 with 124,000 miles that was being sold due to a engine noise (sounds like rattling then it makes a clang).

I removed the serpentine belt and started the vehicle and the noise did not change.

I replaced the Camshaft Position Actuator Solenoid (CPAS) with a Dorman part and this did not change the noise.

I removed the starter and the bolts in the flexplate to the torque converter are all tight. I can not see enough of the flexplate to verify that it is not cracked (so, I suppose if the flexplate is cracked it could cause this noise?).

I removed the valve cover and noticed a light wear mark (that pretty much just removed the yellow film) on the inside top of the valve cover (directly over the timing chain). The 2007 I4.2 does not have a top timing chain guide! I went to the dealer and verified this!

Do you think this (timing chain hitting the vale cover) is causing the noise the engine is making?

Due to the wear mark on the inside top of the valve cover, I believe I will have to install a new chain and possibly a phazor!

If you have any recommendations, please let me know what they are?

Thanks,

Paul

 

[Sparky]

Is there any slack in the chain?

It could be the source of the noise. Did you verify where the sound was coming from using a mechanic's stethoscope (or a long handle screwdriver on the cover to your ear)?

 

[phogstenjr]

I did not use a stethoscope or any other method to determine where the noise was coming from. I figured with the awful racket it is making, once I took the valve cover off, I would certainly be able to see something worn out or broke.

When I removed the valve cover, I could see a little slack in the chain between the Phazer & intake camshaft gear. After I manually turned the engine over with a ratchet & 15/16" socket to check if the bolts going through the flexplate into the torque convert were tight, the chain was tight on top.

I included 3 pictures of the Phaser, timing chain, & Intake sprocket at TDC. I do not have the timing chain cover off to see the crankshaft gear.

 

[limequat]

My car made a similar noise when the return spring on the cam sprocket broke. It also ran bad.

My 2006 also has no chain guide at the top. This appears to be a cost savings that GM implemented in 2006. My cover also had slight wear marks.

 

[phogstenjr]

limequate,

Are you referring to the camshaft Phaser?
"My car made a similar noise when the return spring on the cam sprocket broke. It also ran bad."

Thanks,

Paul

 

[Mooseman]

Does the noise only happen at idle? If so, then it's likely the chain tensioner. The ratchet mechanism in the tensioner doesn't hold however the oil pressure fed part of it still works at higher engine speed and oil pressure.

If it is that, get ready for the suck:
How to replace I6 timing chain and tensioner

For possible noises from the flexplate, @Capote has lots of experience with that.

 

[Capote]

For possible noises from the flexplate, @Capote has lots of experience with that.

You trying to give me PTSD? lol.
@phogstenjr If you could grab a video of the noise, that'd be great. I could probably help decipher if it could possibly be a cracked flexplate. Have you been under the truck while the truck is idling by any chance yet?

 

[phogstenjr]

Hello,

I never brought the RPMs up (I was afraid of whatever was making the noise, would let loose and cause even more damage).

Capote, Do you think I could use an inspection camera to look at the flexplate through the location where the starter goes to see if it is cracked?

Thanks,

Paul

 

[phogstenjr]

Capote, No I was never under the truck while it was running (the noise seemed to be coming from the front part of the valvle cover). I did not think of recording the noise.

 

[Capote]

Hello,

I never brought the RPMs up (I was afraid of whatever was making the noise, would let loose and cause even more damage).

Capote, Do you think I could use an inspection camera to look at the flexplate through the location where the starter goes to see if it is cracked?

Thanks,

Paul

You don't need to go through the starter location. Just remove the rubber boot that sits in the bottom of the bellhousing and rotate it with a big screwdriver whilst looking for any sort of fractures. If you just use an inspection camera, you might not catch a crack because it may be in a blind-spot or area where the inspection camera won't fit. It's very tight between the torque converter, flexplate, and end of the block. When my origional cracked, it sounded like it was coming from the top as well.
From what I've experienced, the noise a cracked flexplate will make while rotating will emanate into the block, making it appear to be coming from the head or something. It took me like a week to actually realize where the noise was coming from. I thought it was a spun-bearing at first. I wouldn't worry about RPM's, being that I drove the truck a over a week with a cracked one. So if you're sitting in the driveway just revving it up (not to the redline mind-you) i'm willing to bet you'll be all good.

Take a look at this post from my thread when I went about diagnosing the noise and my horrid and quite unbelievable discovery:
https://gmtnation.com/forums/thread...-end-troubleshooting.15534/page-3#post-515350
I recommend you look at the whole thread, might be able to help you out further my friend.

 

[phogstenjr]

OK, I will look under the Trailblazer to see if the flexplate is cracked. What had to be removed to change the flexplate (I have a 4 wheel drive)?

 

[Capote]

OK, I will look under the Trailblazer to see if the flexplate is cracked. What had to be removed to change the flexplate (I have a 4 wheel drive)?

You have to drop the transmission to change it out. I've removed & installed the transmission in these trucks more times than I care to count...

 

[limequat]

limequate,

Are you referring to the camshaft Phaser?
"My car made a similar noise when the return spring on the cam sprocket broke. It also ran bad."

Thanks,

Paul

Yes, the phaser has a spring that pushes it back to zero. Mine broke and made a clanging sound. In retrospect, you might be able to check by pulling the solenoid connector. There's a detent that is supposed to lock it in the zero position until there enough oil pressure to control it.

 

[16vcabman]

Show us a picture of the valve cover. It sounds like you found your problem. Replace all guides, chain, and sprockets. I would check phaser. If it moves easily replace. How many miles? Oh and replace tensioner.

 

[Mooseman]

Oh and replace tensioner.

This is not a trivial thing. It's a huge job.

 

[limequat]

I'm not sure the valve cover interference is abnormal. Both of mine (2006) showed signs of rubbing. Maybe it would be worth installing a 2002-2005 upper chain guide for peace of mind.

 

[Mooseman]

If there is room in there but it's a good idea.

 

[16vcabman]

It is a pita to change all the chain components. Can you reach down the side with a screwdriver and feel the slack in the chain?