Sticking valves on a new head

Hi everyone new XJ owner here.
Picked up this rust bucket for real cheap a couple weeks ago, had a cracked head.
If I can get it running I’ll probably start a build thread but it’s not running yet...


Anyway I pulled the head and got some new gaskets and other things to replace while I was in there


So I replaced the cracked head with a remanufactured one. Company seemed trustworthy and offered a warranty.

I got the Jeep running and put back together. I have about 40-50 miles on the new head and a valve, I assume stuck, and bent. number 6 cylinder exhaust valve



It left this indentation on the cylinder head. Kinda hard to see at the 12 o clock position. Looks like a pretty insignificant ding.


My theories for the valve sticking are that I either missed some lubrication step. The engine was running very rich, I put in a new O2 sensor that I think solved that problem about 10 miles before I bent the valve, so maybe a bunch of carbon could’ve built up on it, probably not from only 40 miles of driving but I’m not sure. Maybe the company I bought the head from didn’t clearance the valves correctly? I didn’t think the 4.0 is an interference engine. The company also said to adjust the valves, and I was pretty sure the lifters don’t need adjustment so I didn’t do that...

So my questions are what could’ve caused the valve to stick? Is the ding on the cylinder head anything to worry about? And then because I still have the old head can I just swap the bent valve out? Should I swap all the valves? Or do I need a new valve?

I'm suspecting a bad valve job - too tight of a clearance between the valve and the valve guide causing the valve to stick open when it got hot, or it could have been a bad valve that warped when it got hot (I've had that happen before).



The ding in the piston is nothing to worry about - maybe clean it up with some emery cloth, being careful not to get debris into the cylinder. The valve is toast.


If possible I'd take the head back to where you got it and let them fix it.

Tracks said:

So I replaced the cracked head with a remanufactured one. Company seemed trustworthy and offered a warranty.

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You definitely need to take it back to where you got it and have them remedy the situation.

Take the head back to the shop and have them fix the valve guides they are to tight and they should give you a new head set because it is their fault that happened .

I thought the 4.0 was a non-interference engine?

Here are my suggestions:
1. If the head is a re-manufactured one, it may have been re-surfaced too much to get a tight "quench-height". Solution? Install a thicker head gasket.
2. Then place some modeling clay on top of pistons, under valves, and lay head (w/ thicker head gasket) on block and lightly torque head bolts, Install pushrods/rockers/lifters and MANUALLY rotate engine crankshaft a couple of times.
3. Remove head and measure clearance between valves and piston tops. Use razor blade to slice through clay indentation to take measurements. Exhaust valves need more clearance than intake valves due to the hotter exhaust valve expanding more. I typically use GM SBC specs for valve/piston clearances for performance engines.

Engines w/zero clearances between valves & pistons typically bend valves. Bent valves typically score valve guides & valve stems. If the valve is a two piece valve, i.e. valve head welded to stem, the valve head can break off and wipe the engine. I only use one piece SS valves from Manley. Likewise, denting cast pistons typically cracks the cast pistons over time and wipes the engine. I only use forged pistons on my rebuilds.

Best regards,

CJR

CJR I appreciate the reply. That sounds like a solid method for rebuilds.

I submitted a warranty claim with the company, gearhead manufacturing, if anyone’s dealt with them before. So far they’ve been helpful and will pay to have the head shipped back to their facility where they will do an in house inspection.

I’m not supposed to take any of the valves out so I can’t tell for sure what happened. Whatever it was hopefully they determine it was their fault and replace the head.

More updates to follow

Gearhead is sending me another head. Didn’t tell me what was wrong with the other but it wasn’t my fault thankfully. I’m happy with the customer service just a little slow. Hopefully I can have this thing running for real this week.

Measure the deck height and volume on new head. If head has been flycut, you need to know it, and adjust gaskets to accommodate. if not, you may end up with too high compression ratio. this need be checked prior to assembly. The builder may also be a trustful source of info on this, so ask if you dont have the ability or time to measure this yourself. get the deck height and chamber volume info, then you can calculate your compression ratio.

Keep a Jeeping!

It is, but that assumes the valve does not go down below the valve train limits. Busted spring (or?) might let it go down too far?

lawsoncl said:

I thought the 4.0 was a non-interference engine?

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