Greetings,
My 4.0 just started making this horendous noise. It is a very loud tapping that is more noticeable after it warms up. There is a small crack in the exhaust manifold but I doubt that it would make that loud of a noise. I have put a screwdriver to the valve cover and can hear a tapping noise. I am sure that someone has had similar problem. Could it be a broken spring or rocker arm. I do not want to drive it until I figure it out. How difficult is it to change the upper parts out of the head? Any ideas would be great. I miss my jeep.

Thank you in advance
Chris

 

If it's a broken lifter it's super easy. Just taking the valve cover off wil tell you. Go ahead do it. It's probably leaking anyway and needs a new gasket.

 

I had a similar issue with one of my jeeps.... It can be a number of things - Rod knock, bearing, piston slap, lifter, etc....

Here is a test to perform, to help at least narrow it down a bit... once it starts to make the tapping noise, shut the engine off... pull the spark plug wire off of the first cylinder... start it up, and see if the noise is there... if it is still noisy, shut the engine down again, and plug the wire back in, and pull the wire off of the next plug and repeat....

In essense, you are "turning off" ( for lack of a better word) that cylinder... I would think that a lifter would still make noise, even with it's corresponding plug wire pulled... where with a rod knock / bearing, as there is no "load", it should quiet down. IN addition, this will tell you which of the cylinders is the source of the noise...

Do this test, and let us know....

 

mine did the same thing a couple months ago. i had to run it for a few days to work and back. on the 3rd day on the way home to tear into the top end it all at once just when away, and no noise after that. this was just after filling up with fuel from an out of town gas station. i talked to another jeep mechanic, and he said he has seen several that "knock" really bad when trying to fire on bad, or watery gas. hopefully thats all it is, but good luck.