Intermittent Noise from front of valve cover

[gmtofd]

At 185K miles, my wife '04 4.2 Trailblazer developed a intermittent tapping noise at driver's side front of valve cover, it can be felt when placing a hand in the area. No codes and it runs fine. Would like someone to confirm my assumptions that it's the timing set has to be replaced?

Thanks

 

[mrrsm]

This is what all the related hardware under the Timing Chain Cover looks like when everything is in order. But because the Intake Camshaft and Sprocket along with the upper Valve Train hardware can echo noises into that same area under the cover... listen and feel on the Intake Valve Cover side towards the front #1 Cylinder and see if you can feel or hear any tapping that might indicate a broken valve spring up in there as well. Normally... most of the racket in this arrangement happens on the "Slack Side" at the passenger area due to the Tensioner and movable chain guide being located in there:

http://s557.photobucket.com/user/60...ENGINEREPAIR/TIMINGCHAINDIAGRAM?sort=3&page=1

 

[Mooseman]

Condensed version, it could be your timing chain tensioner. If you can record a video of it, I can confirm. If it also goes away above idle, it's the tensioned.

 

[gmtofd]

Thanks for the replay fellas. I'll check for sound, I'm not that great at recording audio, perhaps I can get my wife or son to help.

 

[gmtofd]

IDK how to do and audio post, but upon listening again, I'll have to revised the symptom as the noise is coming from the passenger side. The random tapping is there regardless of rpms, seems it gets louder as it revved up.

 

[Tiggerr]

IDK how to do and audio post, but upon listening again, I'll have to revised the symptom as the noise is coming from the passenger side. The random tapping is there regardless of rpms, seems it gets louder as it revved up.

Exhaust leak maybe?

 

[gmtofd]

Plan on removing the valve cover, this weekend with the hope that its a loose upper guide plate. Thanks for the input about an exhaust leak, something is definite bouncing off the front of the valve cover.

 

[mrrsm]

If the Valve Cover Gaskets are flattened out and level (or even submerged in the grooves) after their very long OEM life... One of these new gasket kits is a handy thing to have for replacing all those old ones before it gets buttoned up back on top of the engine:

http://www.rockauto.com/en/catalog/...2l+l6,1424281,engine,valve+cover+gasket,10710

 

[Mooseman]

If you can feel something flopping in the front of the cover, it could very well be the chain tensioner. If the noise,flopping disappears when you increase RPM, I would be 90% certain.

 

[gmtofd]

Removing the valve cover shows nothing, no inside marks left from the chain hitting the cover which I was sure was going to be present. Up until now it seem the noise was coming from the timing set, but after looking at an engine at the junk yard that I was considering buying as it was supposed to have been driven into the yard, it had about the same chain slop as mine, the upper guide had more wear than mine.

My son who has a lot better hearing than me, says the noise is coming from the bottom end, up front. Is it a rod knock? draining the oil, cutting up the filter show nothing, no metal.

Again, this is a random clacking noise which frequency increases as the rpms are raised.

Compression test shows, #150 for cyl #1, #80 for #2, #230 for #3, #180 for #4, #230 for #5. Perhaps the bearings are gone for #2, the deck height is greater, which results in low cranking compression? What is perplexing is that the motor runs fine, steady idle. The only thing the wife notices is that the fuel mileage dropped, about 20mpg lately.

Anyone need a good rebuilt L60 trans, that has 80K as it's starting to look like this truck is going to get parted out?

 

[Mooseman]

I would imagine the bearing would have to be basically gone to affect compression. Maybe the piston broke a land and causing some noise with lowered compression. Either way, it has a mechanical issue to lose compression like that.

If you do part it out, you can certainly post in the for sale section.

 

[gmtofd]

After looking at another junkyard 4.2 that has rusted cams, (evidently these mtrs can't sit around too long) had the brainstorm of locating another TB on CL. At first, was looking for something being parted out had a running engine, then thought about finding something, that's turnkey and when the trans dies on whatever is brought, I'll swap the good trans out of the TB presently sitting in the driveway, (that's soon going be parted out).

 

[gmtofd]

Solved the TB engine noise problem by buying a '09 Saab 9-7x with a 5.3. After dropping a $500 deposit on it, then found out about the dreaded AFM (Active Fuel Management) and the associated oil consumption problem that AFM causes, oh well on to the next problem vehicle. At least the wife is happy.

 

[Mooseman]

You can have AFM disabled via a tune or alternatively this way:
How to disable AFM/DOD at no cost

The problem with collapsed lifters is when it tries to reactivate so if you keep AFM from deactivating the lifters in the first place, you can avoid the issue. Check out this FAQ on the 5.3 which has a whole section on the AFM.
FAQ: Vortec 5.3L V8

The fuel savings with AFM is not that great so you won't miss it much.

Enjoy the 9-7x. I know I love mine.

 

[Sparky]

I've got a 5.3 in my Silverado with AFM, I tuned it out, and it has been fine. 163k and counting.