valve tap? burnt valve? something making noise

[702_MJ]

so the motor started making a noise that kinda mimics an exhaust leak, then I was thinking maybe a burnt valve, but i don't know how to check. Kinda just shootn in the dark, cuz I don't know what it is. Its a 92 4.0 142,xxxmi, Anyone want to throw in their .02?

[kro10000]

Its a jeep, a valvetrain noise is the norm :thumbsup:

[702_MJ]

I know valve train is the norm, but it sounds like an exhaust leak. Maybe ill go get some lucas and dump that in during this next oil change.

[jimoshel]

If it is a burnt valve you want to fix it before it burns the seat.See if you can isolate it to one cylinder. Pull one plug wire at a time. Will tell you which cyl is bad or making the noise.Take a compression check on that cylinder.If it's reading below 110PSI you have a problem.Sometimes on a small leak a compression check won't reveal it. Now you have to do a leak down test.Borrow or buy an adapter so you can hook a air supply to the cyl. I have made them by using an old spark plug but for the time and trouble just buy one.Run the piston to top dead center. Attach an air hose to the adapter. need a pressure guage in the air line. Fill the cyl with air,120-150psi.Turn the air off. watch the guage, it should hold the reading. If it starts bleeding down your losing compression. Listen at the carb or TBI for air leak.that's intake valve. Listen at tail pipe.Air leak is exhaust valve. Remove oil filler cap. Air leak is rings. And Jeep or not they should not be making loud valve train noises.

[702_MJ]

so pull the wires while its running? I think my boss has a compression tester i can borrow.

 

and what if it burns the seat? can't machine the seat again?

[jimoshel]

Yes, while the motor is running. The engine drops rpms thats a good cylinder. It stays the same then it's a dead cyl. Insulated fuse pullers works good for pulling a "hot" wire.If you have a burnt valve then all the heat is going out that hole. It will burn the seat. Seats are very expensive to replace.

[dasbulliwagen]

if it sounds like an exhaust leak, maybe its an exhaust leak. These engines are well know for busting the rearmost and frontmost intake exhaust manifold studs, could just be leaking at the exhaust manifold gasket. Take a look and see if the studs are still in place and take a section of heater hose and see if you can narrow down where the noise is coming from. The simplest explanation is usually the correct one. Good luck!

[702_MJ]

That was my first thought was exhaust leak at the rear cylinder, but couldnt really see any signs of the sorounding area being covered in black exhaust.

 

Ill do the plug pull today.

 

Thanks

[jimoshel]

Dasbull is correct. Look for the obvious first and try to correct it without digging into the motor. When I read 'burnt valve' my mind jumped to warp speed. However I stand by my recommendations for testing if it isn't an exhaust leak, Rereading the symptoms, it very well could be an exhaust leak. Besides the manifold to head gasket the doughnut gasket between manifold and exh pipe is also a leaker. Hose trick should work.

[702_MJ]

yeah i keep trying to tighten up the header to headpipe bolts but no luck. It needs a tune up too, so maybe ill start with that and go from there. Explain this hose trick please, never heard of it?

[jimoshel]

Take a hose, size not really important.Heater hose works good. I prefer rubber over plastic.

Put one end to your ear. Use the other end as a probe. Go around the gaskets or any suspect area listening for any noise. The hose acts just like a stethescope and magnifies any noise.

[702_MJ]

oh gotcha thanks

[exjay33]

Could just be the 4.0 piston slap does it go away with just a little bit of rpm added to the engine? If it does it is just piston skirt slapping not really anything to worry about for a long time. If your engine is not to dirty check to see if you can see the cylinder rating on the side of block should be in white or yellow metal marker a thru d a being the best d worst . They started grading them after they replaced a lot of motors due to piston slap. There would be a miss in the exhaust note if u burnt a valve . It could be a weak lifter add a quart of trans fluid to crankcase take for a short drive around town then change your oil .

[702_MJ]

Nope, when you give it a few rpms the sound doesnt go away. It kinda gets drowned out by exhaust noise I think. LOL, block is dirty so I don't think I'll be able to find that letter. Ill add the atf and change the oil. And if its still there I'll use the hose idea.

 

Its probly just an exhaust leak, and I'm probly just being paranoid.

[comanche09]

Some Seafoam in through the brake booster vac line will show an exhaust leak pretty quick.

 

Thats how I found my exhaust manifold crack. White smoke from the rear of the manifold. (I have the exhaust leak "ticks")

[702_MJ]

Yeah ,it "ticks" thats a better sound descritption. But I was listening to it when I was driving and its loud on start up but after driving at highway speeds it tones down, but you can still hear it. So maybe a lifter has some gunk in it an is getting stuck or maybe something mentioned earlier in the thread.

 

But it sounds like its ticking right infront of me, like the headpipe donut gasket is bad or theres a crack, but the header shouldnt crack its a banks header they had "won't crack" on the box!!