A Repetitive Manifold Problem

[Gary747]

1990 Wrangler, 4.2 6 cylinder, EFI Fuel Injection

For several years, especially in temps below 30°F, after running awhile at cruising speed, a loud whistle would come from the engine compartment when I removed my foot from the gas pedal (throttle plate full closed). The whistle wouldn't last long enough to pull over and check it out. I ended up replacing that engine for other reasons, and the new engine didn't whistle any more.

For a while, anyway. Eventually, the whistle came back, getting worse over the course of a year and began to occur at warmer outside temps. I started carrying a mechanics stethoscope to try and capture the event.

That finally happened on a lonely stretch of road where I could stand on the brakes, get out, open the hood and listen to some components before the whistling stopped. It was coming from the gasket interface between the intake manifold and the engine cylinder head. At maximum intake vacuum, air was whistling past the manifold gasket.

I found the two rearmost manifold bolts to be loose, one finger tight. I re-torqued them, but the damage was done... I could not close the gasket junction enough to fix this leak. Also, the exhaust manifold was blowing by in the same relative location. This makes sense because the intake and exhaust manifold share common "hold-down" bolts.

So I had my favorite shop recondition the intake manifold, get me a new exhaust manifold, gaskets, and new attaching hardware. Everything cleaned up nicely and went together tight, torqued to maintenance manual specs. We also had a nearby muffler shop send a welder over to release and reset the exhaust pipe loads on the exhaust manifold, slightly relocating the pipe routing.

Drove about 600 miles including on some rough terrain and took the Jeep back into the shop to check the manifold bolt torque (among other things) and found the 4 most aft manifold bolts to be loose. No leaks, no whistles, but loose bolts. They are tight now, but it is clear to me that between two engines and two exhaust manifolds, the rear manifold bolts work loose with vibration loads over time.

Are loosening manifold bolts a common issue on the inline 6 Jeep Wrangler engines? I have a strong urge to intentionally over-torque those rearmost bolts.

 

[Chris]

Never once heard of loosening manifold bolts, I don't think that's a common issue at all. That's got to be the result of someone not torquing them down properly I would think.

 

[Gary747]

Do folks generally use the "cupped" washers to secure the manifolds to the head? I need to find a source for new ones... they are the only attachment hardware that was reused. These washers are pretty substantial in thickness, but are cupped to provide some thermal flex to the manifold mount points. However, I can imagine that they could allow some manifold movement relative to the gaskets. Does anybody have experience using thick flat washers and not the "cupped" ones?

The "cupped" installation calls for 23 ft-lbs of torque, which is not a heck of a lot, but will not "crush" the cupped washers. Like I mentioned, I am strongly tempted to tighten these thing to more than the spec.

 

[machoheadgames]

Do folks generally use the "cupped" washers to secure the manifolds to the head? I need to find a source for new ones... they are the only attachment hardware that was reused. These washers are pretty substantial in thickness, but are cupped to provide some thermal flex to the manifold mount points. However, I can imagine that they could allow some manifold movement relative to the gaskets. Does anybody have experience using thick flat washers and not the "cupped" ones?

The "cupped" installation calls for 23 ft-lbs of torque, which is not a heck of a lot, but will not "crush" the cupped washers. Like I mentioned, I am strongly tempted to tighten these thing to more than the spec.

On the factory 4.0L, I didn't even torque them when i reinstalled my intake manifold after doing the exhaust header replacement. I just got them nice and snug and it is all still working fine 4 years later. It's too tight to really get a torque wrench in there. I did follow the torque pattern as to get a nice even compression on the gasket, but that's as far as I went to be methodic about it.

 

[Gary747]

I'm with you, machoheadgames. I'm simply going to tighten them by feel while the engine is cold. It's only the rearmost 4 bolts that are giving me a problem.

 

[TimberTim]

Do folks generally use the "cupped" washers to secure the manifolds to the head? I need to find a source for new ones... they are the only attachment hardware that was reused. These washers are pretty substantial in thickness, but are cupped to provide some thermal flex to the manifold mount points. However, I can imagine that they could allow some manifold movement relative to the gaskets. Does anybody have experience using thick flat washers and not the "cupped" ones?

The "cupped" installation calls for 23 ft-lbs of torque, which is not a heck of a lot, but will not "crush" the cupped washers. Like I mentioned, I am strongly tempted to tighten these thing to more than the spec.

My "91" had two of the cupped washers missing. I didn't want to go to the hasel of locating new ones so I simply made my own ! I chucked up a 3/4" or 7/8" Hole saw in my drill press and drilled two plugs from a piece of 3/8" flat plate . the result was two Discs 3/4" in diameter with a hole in the center. I clamped the disc in my vise and used a 1" drill Bit to form the cup on one side. Then I enlarged the center hole to 3/8" and tightened a long 3/8" bolt in the center hole . I chucked the bolt into the drill press and turned it on and used a 4 1/2" peanut grinder to form the chamfer on the out side edge. I didn't harden mine , but if you wanted to harden yours simply, cut the bottom out of a soup can, place the discs in it and add enough used motor oil to cover the discs , add a dash of gas and light it on fire. allow the mixture to burn it's self out and Viola....Two Hardened cupped washers...... the used motor oil is loaded with carbon from the combustion process of the engine and helps in the hardening process..... Tim

 

[Flyer58]

I'm wondering if the 4.0 and 2.4 gaskets are different. My '92 2.4 only had gasket material on the intake ports and the exhaust was metal to metal between the exhaust header and block. If I went with the replacement gasket which seals both int. and exh. ports the flanges on the intake will be slightly recessed so the bolts and washers may not get even pressure applied and the intake may leak. The flange on the intake is about 1 or 2 mm thinner than the exhaust to make up for the difference in the gasket material (OEM design) This leak has been reported to happen when thinner gaskets are used. So far mine is not leaking.

When I questioned it I was told to use a heavy duty/thicker gasket and it will be ok or just cut out the exhaust part so the header flange will set lower.

Was the original 4.0 this way also?

 

[Gilaguy23]

Heres my $.02. #1 potential issue. Rough roads and a exhaust system that does not have sufficent hangers has lead me to what you have going on. I fabbed a exhaust mount from one of the bell housing bolts to cradle the down pipe, 2 years now and no problems. #2 you might try nixing the bolts and using studs and the crimped type copper nuts that are self locking. Dont use Nylocks as the lock ring will melt. Make sure things are torqued evenly. Dorman I IRC sells the uber think manifold washers. If I recall when I did the mani in my 95 the gasket kit had 2 gaskets,one to fully cover the ports or both intake and exhaust. It also came with a thin gasket type material one for just the intake IIRC. That made for the two manifolds not setting at the same plane as far as the washer area went, and using flat washers would not really apply the same force on the 2 manifolds. This is where the cupped washers seemed to be able to use their edge to push the same on both manifolds. That's all I got.