After changing head on 2.5 I lose cylinder 3 when it gets hot

[Tooonz]

I’ve been working on my son’s jeep for months now. It all started when his engine overheated, cracked he head and he ended up with coolant in the oil.
It’s been a long haul and I’m almost ready to admit defeat. Long story short I tried a reman head, it was shaved to much so I grabbed another 2.5l engine from my cousin.
The block looked too scaly so I robbed the head off of that engine , didn’t resurface and it ran awesome. Until it reaches around 150 degrees. Then we lose cylinder 3 on the intake valve.

If I back the rocker arm bolt off a little bit it smooths out. If I tighten it and at temp I have no compression in cylinder 3.

Could someone enlighten me please what might be happening. I tried shimmin the rocker and that made it worse.

Thanks for any help.

 

[Chris]

I’ve been working on my son’s jeep for months now. It all started when his engine overheated, cracked he head and he ended up with coolant in the oil.
It’s been a long haul and I’m almost ready to admit defeat. Long story short I tried a reman head, it was shaved to much so I grabbed another 2.5l engine from my cousin.
The block looked too scaly so I robbed the head off of that engine , didn’t resurface and it ran awesome. Until it reaches around 150 degrees. Then we lose cylinder 3 on the intake valve.

If I back the rocker arm bolt off a little bit it smooths out. If I tighten it and at temp I have no compression in cylinder 3.

Could someone enlighten me please what might be happening. I tried shimmin the rocker and that made it worse.

Thanks for any help.

Based on your description, losing compression in cylinder 3 when it heats up could be indicative of a few potential issues.

Valve Seating Issues: It’s possible that the intake valve for cylinder 3 isn't seating properly when hot due to warpage or damage to the valve or the seat. Since you mentioned that backing off the rocker arm helps, it might be worth checking the valve lifter for proper operation. If the lifter is collapsing under heat, it can cause loss of lift and subsequently compression.

Head Gasket: Even with a reman head or a used head, if there’s an issue with the head gasket, it could lead to loss of compression. A tiny leak that expands with heat could become an issue at operating temperatures.

Rocker Arm Adjustment: The fact that loosening the rocker arm bolt helps suggests that there might be an issue with how that particular rocker arm is positioned or adjusted for the valve. Make sure you’re adjusting it to the right specifications when everything is cold, and double-check the lifter to ensure it is functioning properly.

Crankcase Pressure: Another thing to consider is if your engine is developing excessive crankcase pressure, potentially from a worn piston ring or bad valve guide seals, which can change the dynamics under heat and contribute to poor cylinder sealing.

Heating Issues: Ensure that the cooling system is functioning correctly. An underlying cooling issue might also cause problems with the engine’s performance at heat.

It could be worthwhile to do a leakdown test specifically on cylinder 3 to help diagnose whether it’s losing compression through the valves, rings, or possibly head gasket issues. Sometimes pinpointing the source of the problem requires a bit of detective work.

 

[JustDandee]

Hydraulic lifters on this motor, correct? Cold oil pressure is sufficient to keep it pumped up warmed up oil not so much?

 

[Tooonz]

Hydraulic lifters on this motor, correct? Cold oil pressure is sufficient to keep it pumped up warmed up oil not so much?

Yes hydraulic lifters and non adjustable rockers.

 

[JustDandee]

What weight of oil are you using? Perhaps trying a heavier weight oil like a straight 30w could see if you get improvement? By improvement meaning that runs well until it gets to higher temp but necessarily full operating temp. What I have is a hypothesis that the lifter has failed on your intake side, no compression because the cylinder can get air in…

Hoping someone with more experience might chime in to shoot holes in that idea or support? just trying to tease out what mechanically can change going from cold to operating temperature that would effect the valve train… Oil viscosity and hydraulic lifters I think is a possibility.

 

[Tooonz]

What weight of oil are you using? Perhaps trying a heavier weight oil like a straight 30w could see if you get improvement? By improvement meaning that runs well until it gets to higher temp but necessarily full operating temp. What I have is a hypothesis that the lifter has failed on your intake side, no compression because the cylinder can get air in…

Hoping someone with more experience might chime in to shoot holes in that idea or support? just trying to tease out what mechanically can change going from cold to operating temperature that would effect the valve train… Oil viscosity and hydraulic lifters I think is a possibility.

10W30, is what I am using, we didn't have any lifter issues prior to removing the head. Could letting is sit for a couple weeks be bad for a lifter? could the old oil be still in the lifter? the oil with the coolant in it? I have changed the oil twice so far since cleaning the old oil out.

 

[ColoJeep]

10W30, is what I am using, we didn't have any lifter issues prior to removing the head. Could letting is sit for a couple weeks be bad for a lifter? could the old oil be still in the lifter? the oil with the coolant in it? I have changed the oil twice so far since cleaning the old oil out.

Sounds like a valve guide is on the tight side and it might have a weak/broken valve spring on that cylinder . It's not oil/lifters in my opinion.

 

[JustDandee]

Sounds like a valve guide is on the tight side and it might have a weak/broken valve spring on that cylinder . It's not oil/lifters in my opinion.

I like this idea better than mine. Assuming no spring issue any thoughts on a backyard means to free the guide in place? Maybe some penetrating lube on the cold engine and see if it will self polish/clean with a few heat cycles?

if not I suspect then the original poster would need to pull the head again… which I am sure sucks at this point.

 

[Tooonz]

I like this idea better than mine. Assuming no spring issue any thoughts on a backyard means to free the guide in place? Maybe some penetrating lube on the cold engine and see if it will self polish/clean with a few heat cycles?

if not I suspect then the original poster would need to pull the head again… which I am sure sucks at this point.

Yes;ulling tghe head would suck but at this point, that’s not out of the question. It’s such a good jeep, in really good shape.

 

[Moglocker]

Yes;ulling tghe head would suck but at this point, that’s not out of the question. It’s such a good jeep, in really good shape.

Just get the head rebuilt

 

[Tooonz]

I found a bad lifter on the intake valve for cylinder 3, I’ll check the others later today. But it seems to be running smooth up to 195 degrees now.

 

[ColoJeep]

I found a bad lifter on the intake valve for cylinder 3, I’ll check the others later today. But it seems to be running smooth up to 195 degrees now.

Did you swap out all the lifters ? How was the lifter "bad" ? Glad you have it running good at temp !

 

[Tooonz]

Did you swap out all the lifters ? How was the lifter "bad" ? Glad you have it running good at temp !

I only changed that one lifter, when i pulled the lifter on the bad valve I saw wear underneath, fresh wear, could have been when I put the the machined head we bought originally. That head had too much removed. We had a difficult time even turining the engine over with that head to the point we wore the starter out. I order a bore scope and it will be in tomorrow, I want to see the damage to the cam, and also I want to check the others lifters. Good news is it is running smooth at operating temp. I have a diner engine that had roughly 90K on it that I can take parts from, that lifter was perfectly flat.

 

[Tooonz]

That’s the end of the road, cam is junk. Even though it ran okay with a new lifter . It won’t be long before it tears through the other lifter . I’m going to junk the engine. I do t have much else of a choice with that much metal floating in the engine .