Knocking noise when first starts up

Paytondemarco7

Paytondemarco7

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Joined
Mar 11, 2021
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5
Location
West Virginia
I have a 2000 Jeep TJ 4.0 and the engine likes to knock when I first start it up. After a while this will go away once the engine is warm (I am aware that metal it expands, and these possible gaps get filled with oil). My question is could it possibly be rocker arms needing an adjustment? Before I decide to rebuild engine for some damn lifters. Has anyone had this said problem and adjusting the rocker arms fixed it? Thanks.
 
Really need a video to properly diagnose. The 4.0 loves to make valvetrain noise at startup that should not necessitate a rebuild.
 
Lifter rattle
Exhaust leak on manifold

Are two things that can make a noise at a cold start and taper off as the engine warms.

If your bottom end was bad it will knock pretty much all the time and it is an unmistakable sound. Like a pinball in your oil pan.

Think about what I'm saying. A pinball is heavy and envision it being in your oil pan flying around.

I'll tell you a funny story...
We had a mustang brought in the shop one time for a rat a tat tat noise that was semi intermittent.
Some guys thought it was knocking...i said it kind of sounds like it but I don't think so it's just not a heavy enough rattle/knock. The other thing we came to find was we could change the noise if the PCV valve closed off.

Anyways customer wanted it torn down and fixed.
(I knew this had been apart from someone after it left Ford as the cam was much too radical to be anything Ford ever used)

We pulled the engine...
come to the oil pan and and looky looky here what we found.

A 5/32 deep well socket laying inside the oil pan. 😯😯😯😯

Back to your issue...
A true knock will be unmistakable. If it quiets after a few moments after starting a true knock will show it's ugly self again in higher rpm. Somewhere in the rpm/inertia sequence it will reappear you can count on that.

Good luck
 
If your bearings are shot you will get some knocking. dump your oil in the pan and check for gold looking metal shavings
I had knocking "valve tick" sounds took off the oil pan removed some connecting rod caps saw bad bearings scared crank hand to do a complete rebuild. did the entire engine cause why not.

If you have to replace the lifters rods rockers its really easy and you can do it in like 4 hours if your not a pro. Just need a long very strong magnet and a couple sockets. one of the easiest engines i have ever had to rebuild imtalking cake. didnt even pull the block from the mounts just stripped it in the garage.
 
Loose exhaust system too. if you broke an exhaust hanger it will knock on start up and bumps.
 
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