2002 KJ: Pull the head?

[JerkyPete]

The 2002 (141K) had an episode about a week ago. It started hard and ran real rough. Shut it down until I got a chance to troubleshoot. Next day, went to diagnose problem and Jeep ran great.

Fast forward a couple days and the KJ is again acting up. This time it doesn't fix itself.

I pull all the plugs and 5 are carbon fouled and 1 is wet with fuel. While I have the plugs out I figure I'll Check compression. Slightly warm engine (and throttle shut), but I still get 175/190/184/185/179/0.

The number 2 cylinder (the one with the wet plug) has zero compression. I pull the valve cover and the rocker arm for the intake valve got thrown. Looking around, it doesn't seem to have caused any collateral damage.

My question is what options can I exhaust before ripping the whole engine apart to remove/examine the head? The intake valve is obviously seriously leaking and leading to the zero compression. It could be a bad/bent valve or maybe the press-fit seat is compromised. Is it worth throwing the rocker back on and seeing if the valve starts cooperating. Or do I risk further damage with that approach. Does it ever work to spray some penetrent around the valve stem to loosen it? The main reason I have some hope of avoiding a teardown is that the problem appeared intermittently. If it was a catastrophic failure type of situation, I don't think the car would have run fine for a while after the 1st incident.

BTW - I've used Mobil 1 from the 1st oil change and everything under the valve cover looks very clean (no deposits at all)

 

[sevenhelmet]

Sorry, but I think pulling the head is the only way to be 100% sure there isn't more damage. My guess is, the rocker arm came off for a reason (seized or damaged valve maybe, just a poor weekend mechanic's wild guess.) If you re-attach the rocker and turn the engine over, you are taking your engine's life in your own hands. :freak3:

 

[k99jk99j]

some people have success with putting the rocker back in, and running it after a compression test. but some of the leading causes of rocker arms spitting out are 1)dropped valve seat, 2)carboned up sticking valve, 3)valve spring breakage, 4)lash adjuster getting weak.

has the vehicle been overheated? that would point you in the direction of #1
how clean is the valve train? any sludge?

it could have been an isolated incident but maybe not! my bet is something is getting close to being out of spec in the valve train.

 

[JerkyPete]

Many thanks for the advice...

Because I'm getting zero compression, I think the issue must be the valve itself.

A bad lash adjuster certainly might cause a thrown rocker - but not result in a valve stuck open once the rocker goes on vacation.

I visually checked the spring and it doesn't look damaged. I also tried wacking the valve head with a hardwood rod and mallet and the valve certainly doesn't appear weak. If anything, it feels like the valve is seized.

The Jeep has been getting a lot of short trip duty as of late so carbon could be a possibility.

I have never overheated the engine and everything under the valve cover looks sparkly and new, but maybe the seat is loose anyway (141k on the motor.)

I guess I'll have to pick up the FSM and start dismantling this thing before it gets too cold.