Engine knock?

Tiny
ONNIK1966
  • MEMBER
  • 2007 CHEVROLET TAHOE
  • 4.8L
  • V8
  • 2WD
  • AUTOMATIC
  • 154,156 MILES
Hello, I'm a mechanic at an independent shop and I recently took over someone else's job because they quit. The other mechanic had a rear main seal to replace and an oil pan gasket to replace and valve cover gaskets to replace. He also had exhaust gaskets to replace but did not notice that the exhaust stud was broken in the left cylinder head. So, my problem is, is that this broken exhaust stud on the driver's side in the back next to the firewall was not accessible with an angle drill. So, I removed the cylinder head and drilled out the stud and re-tapped it and proceeded by installing a new head gasket, exhaust gasket, and new intake manifold gaskets. After the repairs were done I started the vehicle and noticed a bad knocking noise coming from the back of the engine. I thought maybe I've done something wrong so I removed the valve cover to see if maybe the push rods were put in wrong, but they are all the same size and in perfect condition, reinstalled the components and started the vehicle again and noise is still there. So, I started thinking that maybe the other tech may have installed/or not installed something wrong to cause this problem. So, my question is, could putting on a new head gasket cause this problem because not the one side has better compression that the other side?
Wednesday, July 5th, 2023 AT 1:29 PM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,854 POSTS
The head gasket shouldn't affect the compression problem, it sounds like foreign metal such as a washer or small bolt is in the combustion chamber. I would remove the spark plugs for the engine and check for damage to one of them.

This guide may help:

https://www.2carpros.com/articles/understanding-and-repairing-engine-knocking-noise-an-in-depth-guide

Can you please shoot a quick video with your phone so I can hear the noise? That way I can tell for sure what's going on. You can upload it here with your response.
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Thursday, July 6th, 2023 AT 6:51 PM
Tiny
ONNIK1966
  • MEMBER
  • 2 POSTS
I just saw your response, I had taken the spark plugs out prior to asking the question and went in with a camera that I bought from the Snap-On tools couple of years back, and nothing was in the cylinder. One of the other mechanics stated that it might be a twisted lifter turned in the wrong position as if the roller was not sitting properly. So since I had already pretty much taken this thing apart I figured what the heck, let's take off the head again and inspect that. So, I did and didn't really see anything right away until I looked harder and then I noticed that the #7 piston had a small mark on it then I looked at the head and that it also had the same mark on it stating to me that the piston was slapping the head. But as I stated in my last text, the engine was running very smoothly with no miss fire or any codes for running rough. So, any input on that, because at the moment we talked to the customer and stated all the things that I have done and he advised us to replace the one piston, rings, rod, and the bearings and put it back together and he was going to take that chance at this time. So now we are waiting for parts. Do have any other input for me?
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Friday, July 7th, 2023 AT 8:24 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,854 POSTS
Can you upload an image of the mark, how bad is it? These engines have different length piston rods FYI. He might have the wrong one installed.
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Saturday, July 8th, 2023 AT 10:45 AM

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