3.7L broken valve spring.

[trail rated]

Sorry, but I haven't been posting here for quite some time.

Anyway, our KJ has a broken valve spring (intake, #4 cyl.) and I have a few questions.

1) What causes a valve spring to break?

2) I drove 40+- miles with the valve hitting the piston, should I pull the heads?

3) My cats were glowing red, are they damaged?

Kinda sad that a vehicle with just over 122,000 miles has a major engine issue.

 

[kj924]

It may not be the valve spring that broke, maybe the retainer for the valve stem.

And yeah I think pulling that head will be in your future *rubs crystal ball*

Cats glowing red....unburned fuel going downstream in the exhaust I would imagine. I don't think the cats are damaged.

 

[LibertyTC]

Engine work...

Did you run synthetic oils, just curious. I would want a compression reading from the good cylinders if possible.
122k miles is not that much but moving parts sometimes do and will go bad. These heads do get hot and may not be the strongest.
I would have both heads rebuilt, timing chain, and water pump, if it has never been done while there.
Please let us know how you do on these repairs.
Best o luck...

 

[sleeve]

The KJ valve springs are weak and are prone to failure with high mileage KJs.

You probably did some real harm to the piston and cylinder head after driving for so long with a bum engine. Please pull the head or take it in for repair.

Not sure about the cats... glowing red though?

 

[tjkj2002]

The KJ valve springs are weak and are prone to failure with high mileage KJs.

Actually they are not,with over 2million+ 3.7's running around the world if you have 1000 failures that is not common,heck even 10,000 failures is not common yet.The KJ uses the same springs as the 4.7 V-8 and there is no problems with them,many have exceeded 250,000miles with no issues.

 

[trail rated]

Did you run synthetic oils, just curious. I would want a compression reading from the good cylinders if possible.
122k miles is not that much but moving parts sometimes do and will go bad. These heads do get hot and may not be the strongest.
I would have both heads rebuilt, timing chain, and water pump, if it has never been done while there.
Please let us know how you do on these repairs.
Best o luck...

Well, the previous owner never used syn, and it was overdue for an oil change when we bought it. I use syn in all of our vehicles.

The comp in the #1 cyl (good) is 150-155 PSI.

I don't have enough time or money to replace parts that are not needed (yet ), you see, I'm doing this by myself, and the Jeep needs to be on the road by the end of this week.

 

[LibertyTC]

Shop Manual

These types of repairs are best left to professionals. I would only attempt such a repair once I had read the shop manual (available from library) and then decide if I am capable, with tools including torque wrench, of doing it myself.
I assume that some local engine/machine shops could remove and machine the heads with necessary repairs, and complete the installation for you.
Let us know what happens in any case.
Best O- Luck !!

 

[sleeve]

Actually they are not

I am sorry but I fail to believe that.

 

[JeepJeepster]

I wouldnt hesitate to drop a new head on my kj. Not sure why someone that knows his way around an engine couldnt do it.

I would want to check that piston out real good so removing the head wouldnt be the first thing I would do if its been bouncing around on the valve.

 

[trail rated]

OK, so we towed the KJ to a guy who does valve jobs. The valve cover was taken off (by me) and when the guy looked at the spring, he said he thinks everything is ok. Today, he will put in two new springs (exh and intk) and will check compression.

 

[tjkj2002]

OK, so we towed the KJ to a guy who does valve jobs. The valve cover was taken off (by me) and when the guy looked at the spring, he said he thinks everything is ok. Today, he will put in two new springs (exh and intk) and will check compression.

Know way to tell the valve condition unless you pull the head and disassemble it.99% of the time if the valve hit the piston that valve is bent,might have damaged the piston also.As for the glowing red cats they are most likely damaged also.

sleeve Quote:
Originally Posted by tjkj2002
Actually they are not

I am sorry but I fail to believe that.

It's not common,you just hear about it more on forums like these which represents less then 1% of the total # of engines in use.

 

[trail rated]

Know way to tell the valve condition unless you pull the head and disassemble it.99% of the time if the valve hit the piston that valve is bent,might have damaged the piston also.As for the glowing red cats they are most likely damaged also.

It's not common,you just hear about it more on forums like these which represents less then 1% of the total # of engines in use.

He says the valve isn't sticking out far enough for the piston to hit it, I don't believe him because the knocking sound was horrible. Anyway, he needs to get a smaller spring compressor because the one he has doesn't fit, Snap-On will bring it in tomorrow.

As for this being common or not, I talked to a Jeep tech Monday, he says this is a fairly common problem and that he has seen the springs break on many 3.7s, 4.7s, and 5.7s.

 

[belvedere]

He says the valve isn't sticking out far enough for the piston to hit it, I don't believe him

I wouldn't, either. I'd be pulling the head.

 

[JeepJeepster]

I talked to a Jeep tech Monday, he says this is a fairly common problem and that he has seen the springs break on many 3.7s, 4.7s, and 5.7s.

Ive never heard of a valve spring breaking on a hemi..

 

[trail rated]

Ok, the valve is bent. Going to have to take the head off now.

 

[HoosierJeeper]

Ive never heard of a valve spring breaking on a hemi..

Has happened on a few Durangos(w/ HEMI) I know of.....luckily not on mine....

 

[JeepJeepster]

Has happened on a few Durangos(w/ HEMI) I know of.....luckily not on mine....

A few? I bet there have been a few randomly catch on fire while driving down the road also...

 

[HoosierJeeper]

A few? I bet there have been a few randomly catch on fire while driving down the road also...

A few of those also....it was a recall with the instrument cluster. All the cabin lights would come on, then you have nice bon fire!!! Ours never did it....thankfully.

 

[Powerslave]

IF these motors are what's called an Interference Motor, then a stuck open valve will hit the piston. A non interference motor will not allow the valves and pistons to collide, no matter what happens, unless the valve falls IN the cylinder; be it a timing chain/belt breakage or a valve spring issue...

Basically, if the piston and valve paths "interfere" with one another, and incorrect timing in their movements result in the piston and valves colliding, it is an "interference head" or "interference engine", and includes virtually all diesel engines. Most foreign car engines are interference motors. If the retainer clip breaks, I think the valve WILL extend too far down and hit the piston head in any case. You would know when/if that happened, the piston head would probably split, break, whatever, that is NOT a good thing. Valves are inserted through the cylinder side, right? SO, yeah, if the clip brakes, it's falling in...

I have HEARD cars that run with a valve open, and was a non interference motor. If the intake valve is open, then you have a real problem, as you push air & gas back up through the intake on the compression stroke, and out the TB area spraying the gas out it. I have seen that, and it makes a LOT of noise. IF an EXHAUST valve is open, then the air & gas goes out the exhaust during the compression stroke, thus the unburned fuel goes out, and will ignite in the hot exhaust. I would rather have an exhaust valve open, than an intake one open.

I think these are NON INTERFERENCE engines, so you can run them broken like that, and not cause the damage to the piston and head that an interference motor would.

As far as the weak valve-train, it's not an issue with a low failure rate...

 

[trail rated]

I think these are NON INTERFERENCE engines, so you can run them broken like that, and not cause the damage to the piston and head that an interference motor would.

I wish that was true!
The intake valve broke, which caused all of the fuel and air to be pushed into the #1 & #2 cylinders, which caused them to misfire, which caused the Jeep to run on only 3 cylinders.

The engine was making a bad knocking noise, it was from the piston hitting the valve. Since the valve is bent, that means these engines are interference engines.

I wish the KJs had a 4.0 instead of the 3.7 protest.gif