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Discussion Starter #1
Hello everyone, I'm new to the forum here. Just did an introduction in the new members thread. I just picked up a 08 Trailblazer SS with a ticking/knocking sound so now I'm here for some advise. I know there's a lot of ticking threads already flying around but I am trying to see if mine is different. Basically want to figure out if it's a rod bearing or lifter that's causing it. The sound seems to be coming from driver side head kind of towards the center of the intake manifold. I went out and bought a mechanics stethoscope but feel like I really haven't figured out how to properly use it. I'll give it another try later today after work. I can also here the sound from the bottom of the engine bay pretty clear. It sounds a bit different then the videos I've seen of rod knock tho. What seems weird to me tho is that it doesn't make any noise on a cold start until about 2-3 minutes after it warms up a bit. Also when put in gear and hold the brake and give it some gas to about 1k rpm under load the sound is completely gone. If I give it more or as soon as I let go it comes back tho. Truck is stock with magnaflow cat back with about 110k miles. Everything else seems to be fine with it and seems to run pretty good. So I want to see if anyone that's had a bad lifter had theese symptoms as well. Glad to be a new tbss owner and new to the forum and Thanks for any help in advance.

https://m.youtube.com/watch?v=0doC1dqxg-A&feature=youtu.be
 

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Premium Member
2008 TrailblazerSS
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12,862 Posts
It is good you are glad you are a new TBSS owner, but sounds like you need a rebuilt short block like Jakey stated. Your pockets might not be so glad soon.

~Aerodynamics are for people who can't build engines~
 

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2008 Trailblazer SS
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2,764 Posts
If the inside of that motor looks anything like the outside, the previous owner might have not kept up with some of the maintenance...including keeping the oil full. What are your goals? Were you planning on keeping it stock? If not, now's a good time for an upgrade. Good luck with the fix.


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Discussion Starter #5
Thanks for the input, the sound in person actually isn't that loud. It seems like the camera amplified it. The engine doesn't seem that bad just a bit dusty from sitting for awhile. Goals with it are to just do a cam, headers, intake, and a tune. I still feel and hope like it might just be a lifter so I'll start pulling the head off. If that's not it then I'll just have someone rebuil the whole bottom.
 

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Discussion Starter #7
I see, maybe I'm just in denile and hoping. I guess since it stops at a certain rpm under load I thought maybe that meant that it wasn't a rod bearing but I'm new to this so I have no clue.
 

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Discussion Starter #8
I also read that the oil pressure suffers when a bearing goes out. Mine seems to be fine so far. Not sure if it takes a while for the pressure to dip or what. If I loosen the valve cover and run the engine and then slightly lift the cover while running should I be able to hear the tick louder through the gap in the cover or should it stay the same since the lifter is further down in the head?
 

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Discussion Starter #10
True, Is it normal for a rod bearing to be completely quiet at a certain rpm tho or should it be constant? I guess the same question could apply to the lifters. I guess maybe it's a sweet spot where it's not flapping all over the place.
 

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Midgets with hammers
'06 TBSS AWD
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Either stop running it and rebuild it, or continue running it and be prepared to put a rod thru the block. Which WILL cause a slight drop in oil pressure....
 

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2008 Trailblazer SS
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The dash gauge for oil pressure is far from accurate btw. Don't use it as any true indicator.


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TrailblazerSS
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Drain and check the oil and cut the filter open. Thats the easiest and cheapest place to start. If you see metal then its a bearing. If not it could be a cracked flexplate, bad lifter or something else.
 

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2008 Trailblazer SS
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If it gets louder once it warms up it's a rod bearing most likely. As the oil warms up and thins out the noise will get worse. If the noise was there at cold startup but went away once warmed up it would be either piston slap or maybe a lifter I suppose. But that's not the case here. Check the oil and filter for glitter if you want to know for sure.


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Discussion Starter #16
Thanks I'll be draining the oil in a bit to check for small metal shavings. If rod knock gets a bit worse once the engine warms up then that's most likely what I have then. At start up there is no knock at all for the first several minutes then it slightly starts coming in
 

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2008 TrailblazerSS
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Thanks I'll be draining the oil in a bit to check for small metal shavings. If rod knock gets a bit worse once the engine warms up then that's most likely what I have then. At start up there is no knock at all for the first several minutes then it slightly starts coming in
Yes, when the mechanical parts heat up, the flawed mechanical parts tolerances begin to change...for the good or the bad. I think most have drivin you in the right direction on what is more than likely the issue, even if it is not what you were hoping for. Most of us without an oiling mod or the modified oil pickup tube run 7 quarts of oil to help prevent the oil starvation upon heavy standing stop accelerations. Good luck with getting it fixed.

~Aerodynamics are for people who can't build engines~
 

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If you're going to drain the oil, take a sample and send it off to Blackstone Labs for an analysis. They'll be able to tell you what metals are more present and you can usually narrow it down to what parts are failing due to which metal different parts are made of. Just a thought... Hope it's not too bad!!

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Mine was even quieter and needs all forged pistons and .005 over hone since they scored the bores. I thought it was a rod but you just never know till its out and it sounds like you need to pull it for sure.

Blackstone said my oil was high in iron and they were correct since the cylinder sleeves were wearing.
 
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