Lifter tap? (not the usual tick-tick-tick)
 

Our '08 Rubicon sits a lot now that my stepson is away at school. He came home this past weekend and started using it again. Upon startup, it now has a very loud tap in the engine. It's not going away. It quiets down under a load, but returns loudly when you pull in the clutch (removing the load) and at idle. It gets louder/faster with RPMs. It's definitely up high - like valve train - and on the left side. I'm pretty sure it's not a rod bearing - I've had those go bad and the sound is deeper, lower and doesn't favor one side or the other as much. This is more of a tap than a knock. And a rod knock usually turns into a death screech pretty quick.

So I'm wondering if I have a collapsed or partially collapsed lifter? I know valve train noise is common on these, how about lifter failure? Is there something else in the valve train I should be looking at? Replacing the lifters is not hard but very time consuming because you have to remove the heads. I'd rather not do that unless I'm 100% sure that's what the issue is.

If I suspected a bad lifter, I would idle the engine with the valve cover off to verify whether or not the noise is a lifter. I have done this on many engines, but not on the 3.8L engine, so I don't know if the potential oil spray is manageable.

A light tap can be caused by excessive leak down, or partially stuck plunger.
It can also be caused by a worn guide, or unseated valve spring. If it is the guide or spring, applying a side load to the spring will reduce the tapping sound quite a bit.

A heavy tap can be caused by a completely collapsed lifter.

Thanks. I don't know about the oil spray on this one either. Some are really messy, some aren't. I also haven't looked close enough at it to see if I can remove the valve cover and still be in a position to start it. I'm not sure what's in the way. It's a pretty heavy tap - not subtle at all. I guess the next step is to remove the valve cover.

Lifter tap
 

I have an 07 and the same thing was happening to mine. I pulled the valve cover off and saw that the rocker arm rail came loose and a rocker (the one closer to the front of the motor)was not on the lifter and was on the spring. I was very happy to see that! Easy fix, so i loosened the rail and put the rocker where it is supposed to be and all is good.

Man I hope I get that lucky.

Totally unrelated, but a similar thing happened to a mower I bought on Craigslist. It was dirt cheap for a John Deere so I scooped it up. Got it home and only one cylinder on the Kawasaki V-Twin was firing. Took the valve cover off - a pushrod had fallen out. Popped it back in and am living happily ever after.

Well the "tap" deteriorated into a pretty solid bottom-end knock last week. I pulled the valve cover on the left side today (where it seemed the noise was coming from) and it all looked good. Plugs look good too. I'm pretty sure it's spun a main and/or a rod bearing. There seems to be two different sounds, but neither are good.

After doing some research on the 3.8L in the Wranglers it doesn't seem that they're a model of longevity. Since I have emissions tests to deal with, I'm going to have to yank it out and rebuild it. I'd prefer something else but that's not an option.

My engine broke a crankshaft, I bought a running takeout (V8 swap) Was told it had a noisy lifter.. No big deal, right?. I decieded to check the bottom end 1st and found # 1 Rod bearing spun.... Then the puke wouldn't refund any money, as I "got a good deal on a used engine".... I would check the bottom end on any 3.8 engine noise, 1st. Easier than pulling to heads and changing lifters, to then find the noise is deeper.

I ultimately replaced the engine. I don't remember exactly, but there were at least 2 spun rod bearings. Lots of metal in the sump and in the pan. I got a reman engine locally (from Promar) that came with a pretty good warranty. It's been running great (we have about 7k miles on it now) - much stronger than I ever remember. It's not a job I EVER want to do again.

I am on my 3rd used engine, can make one out of the 3, Am replacing the connecting rods with mini van rods (they have bearing tangs on opposite sides of the rod, more traditional than the rods used in the Jeep incarnation of the motor.

My previous 07 JK threw a rod after I sold it, and the new owner let me know about it. No idea how it was being driven, but the Jeep had just over 50k miles on it. It also was an oil consumer, a common issue with the 3.8. I am not a fan of that motor.