Jeep Strokers

Interesting issue that I need the extensive knowledge of this forum to verify for me.

First off...engine is a 4.6L running 4.0L rods and KB944 pistons w/ a Comp 68-231 cam and Comp Lifters, custom length pushrods, cloyes double roller cam gear and chain set, MOPAR performance valvetrain and .010 off the deck.

I have about 1500-2000 miles on the motor and other than a cam position sensor she has run strong and reliable.

Now for my issue. Drove from my house to the gym (less than a mile) with no issues. Went in did my daily deeds and came out a couple of hours later. Went to start her up and she started spitting, sputtering and backfiring something fierce. Shut her off. Tried to start her again and nothing. Got her home and started checking the fuel pressure, timing, distributor alignment, etc. All seemed in normal ranges. Took the oil cap off and stuck my finger in for shits and giggles and found the No. 3 Exhaust rocker arm loose and floppy. So I proceeded to remove the valve cover. I found the pushrod for the No. 3 exh valve just sitting there, out of the lifter pocket and out of the rocker arm. It isn't bent or damaged in anyway and is still of the original length. So, I put it back in and torqued the rocker arm (which was also inspected and verified good) back down. The pushrod is now firmly seated as it should be. Yet I am still anxious about starting er up.

What would cause this to happen? Cam lobe failure? Lifter collapse? Sheer PFM? I'm at a loss...I am trying not to pull the pan if I don't have to. Any advice out there would be helpful. Thanks

Are you sure the rocker was torqued correctly to begin with? Was the bolt loose at all? Did you measure for the proper pushrod length during assembly?

Your running Mopar performance Springs retainers and locks? If so there shouldnt be any coil bind with the 68-231-4.

It could be a collapsed lifter or worn cam lobe.. might want to inspect those. Otherwise the only thing i can think of that could cause this is a tight valve guide (if the answers above are correct).

Proper torque was put on all the bolts, triple checked it...

Yep, MOPAR performance everything...

Guess I'm pulling the pan...argh!

cigarluvr wrote:Guess I'm pulling the pan...argh!

If you've torqued down the rocker bolts this time around, then just start up the engine and see how it goes. It's possible that one of the bolts wasn't torqued down properly during the original build and it just worked its way loose.

Collapsed lifter, worn cam lobe, bent pushrod, sticking valve, etc. What is the preload on the push rod that came unseated? Did you verify the pushrod is still straight?

Muad'Dib wrote:Did you measure for the proper pushrod length during assembly?

OK, for a novice, what is the correct way to measure for the pushrods during assembly?

Will

Does this help?
http://www.compcams.com/Pages/417/valve ... metry.aspx

Easiest way. While rotating the pushrod with your fingers tighten the rocker bolt down until the push rod no longer rotates. Just gently rotating the pushrod so you can feel when the slacken is take up. With a strait edge on the head valve cover flange touching the pushrod, mark the pushrod in some manner. Not too thick of a line. I usually use a machinist square with a sharp edge and just rub it against the pushrod. Now torque the rocker down, wait a few minutes for the lifter to bleed down and then scribe another mark on the push rod. Remove the pushrod and measure between the two marks. The cam has to be on the heel of the lobe. I.e. TDC on the compression stroke. Do the exhaust and intake separately with the push rod removed from the rocker you are measuring.

Thanks for the insight...

Planning on tearing into her this weekend. I'll letcha all know what comes out of it.

OK...I tore into her today and found something that I wasn't expecting. Lobes look good from below and the preload seems good. Engine is still tight as hell.

Started looking around and I think I have bigger issues. The back side of the #3 main journal was overheated and black. Pulled the cap and found the bearing gone and the backside of the throust bearing gone.

So what are my options? What would have caused this to happen?

Probably the commonest cause of a worn thrust bearing is the torque converter not being fully seated in the tranny.

Lack of oil or something pressing on the end of the crank, like a torque converter as dino said.

So is the crank salvageable or do i need to source a new one? It scored the crank pretty good...

Your crank's probably beyond salvage but I suggest you take it to a machine shop and see if they can do anything.

Any idea where i could get an oversize thrust? That's what my machinist recommended?