Why did my 4.0L head get destroyed?

[93_Fummins]

Another thought: The computer can't tell if there is a different cam installed. I wonder if the "RV" cam could have been far enough from stock to create an issue? Running to rich or hot?

The computer can't see individual cylinders, just a total general reading. A single cylinder could be rich/lean but still not escape the bounds of the total reading limits once combined with the other cylinders. You would need individual MAF, IAT, EGT, Knock, and O2 sensors PER CYLINDER to get a true cylinder by cylinder self learning fuel/spark management system.

I realize you have flat tappet lifters; my comment about the roller lifters was an attempt to point out that the spinning of the lifter itself shouldn't have reflected to the head/valve problem you had unless the cam was totally wiped out or the lifter was collapsed, either case barely opening the valve and thus causing the rich/hot scorching situation I mentioned with the EGT comment. The lifters not spinning, let alone, should not be the culprit, imho.

The epoxy comment kind of leads into the poor cooling notion that I had. Not judging the method or application, but curious if something could have happened that altered the flow enough to cause issues. Either way, it was an alteration that has varying outcomes based on varying conditions.

The cam itself should not have caused any issue as long as all the valvetrain was set up correctly. The piston will still only draw so much air in total, and thus only needs so much fuel in total, varied by the air intake sensors....so theoretically, the greater flow of intake air due to the cam should have adjusted the fuel table demand.

I still theorize excessive combustion heat/pressure on that one cylinder as the culprit. But it's just a theory... Too many variables to know for certain.

 

[MomoJeep]

Good points! Yeah, I originally thought I had a bad lifter. I didn't explain well, that what was found when we pulled it apart was VALVE RECESSION. They had pounder their way up into the had and destroyed the valve grind. And this was on all cylinders, not just one. I'm pretty sure it was worse on the exhaust valves. Which makes sense I guess (heat). So do I now conclude that combustion was somehow off and the valves were getting too hot? Or could it be my previous theory that I drove it too hard (I definitely pushed the engine hard).

 

[jpnmaine]

Poorly installed or wrong material of the valve seats...and or excessive valve lash...my guess.

 

[Randyzzz]

Poorly installed or wrong material of the valve seats...and or excessive valve lash...my guess.

Non hardened valve seats combined with mixture too lean, and heavy loads to top
It off?

 

[spankrjs]

I drove a 258 with MPI on multiple cross country trips, 16 hours straight driving at over 75mph, back to back days of this. Scrambler loaded down, two people, all the gear in the back. Put over 40,000 miles on a 258 of unknown condition/miles.

That 40k miles was multiple trips from the bottom of Mississippi to:

Moab, Utah
Harlan, Kentucky
Hot Springs, Arkansas
Silver Lake, Michigan

Plus countless trips all over Alabama, Mississippi, Louisiana, etc. The motor eventually only had less then 5psi oil pressure at idle, and eventually cracked a piston skirt. I still drove it a couple thousand miles with the cracked piston skirt. I ended up rebuilding this motor, it is still in use in my Green Scrambler. The valves/head had some wear, like the rest of the internal components, nothing out of the ordinary like what happened to you.

I think you just had a bum head/valve seats, nothing to do with how you drove, or any inherent flaws with the 258

 

[MomoJeep]

As you guys can probably tell, engines are not my specialty. I have another CAM question. My understanding is that a cam should match the head/valves. But the 4.0L head swap (with MPI) does not include a cam change. So the 258 cam works fine with the 4.0L valvetrain?

In my case, I now have a new cam, and it's the one matched to the 4.0L head. I hope this was the right thing to do!?

 

[MomoJeep]

Non hardened valve seats combined with mixture too lean, and heavy loads to top
It off?

Non-hardened? My understanding is that the valve seats are integral to the cast-iron head, not inserts. I thought they were locally induction hardened?

 

[Randyzzz]

Non-hardened? My understanding is that the valve seats are integral to the cast-iron head, not inserts. I thought they were locally induction hardened?

AFIK, there are valve seats installed into the head. That’s how they are able to rebuild heads with recessed valves.

 

[MomoJeep]

AFIK, there are valve seats installed into the head. That’s how they are able to rebuild heads with recessed valves.

I'm curious, because when I looked at the bad head I removed (out of a '94 wrangler originally) there were no inserts (valve seats) that I could see, just the casting material. There was bad valve recession, but it's hard to imagine that valve seats (inserts) were once there.

Also, see the third posting on this thread. Now I am really curious! Does anyone know for sure? https://www.cherokeeforum.com/f2/valve-seats-144848/

 

[Randyzzz]

I'm curious, because when I looked at the bad head I removed (out of a '94 wrangler originally) there were no inserts (valve seats) that I could see, just the casting material. There was bad valve recession, but it's hard to imagine that valve seats (inserts) were once there.

Also, see the third posting on this thread. Now I am really curious! Does anyone know for sure? https://www.cherokeeforum.com/f2/valve-seats-144848/

Interesting. A non-hardened seat will wear rapidly with unleaded fuel. An induction hardened seat will be wear resistant, but lacks serviceability. I wonder then, do any of the reman heads install hardened seats? My 4.0 in my 2001 Cherokee has a replacement head, and it is tagged “Mexico”.