4.0 exhaust manifold studs - bolts o.k.?

[timba]

I'm replacing the exhaust manifold on a '94 XJ with a 4.0 tomorrow. I started prepping things tonight, and took out the bolt that's towards the front of the motor for the exhaust manifold. I was surprised to see what looked like permatex on it, so I did a little looking into it. Apparently it's supposed to have a stud there and the one at the back. I haven't looked at that one yet to see if it has a stud. Can anyone tell me if there's a problem putting the bolt(s) back where it came from? Should I replace it with a stud? What kind of torque would you put on the stud itself - same as the nut (about 24 ft-lb)?

Hopefully someone has time to respond to this before I get it buttoned up. Thanks!

 

[5-90]

The studs are there to help you keep things aligned while you wrestle the manifolds into place. If you need to replace them, 3/8"-16 threaded rod, cut to length, should work.

I know that the holes are threaded 3/8"-16 on RENIX heads, but I'm not sure about HO. Please confirm - you can just run a 3/8" nut into a manifold screw (confirm the size, since you should replace them anyhow...)

 

[timba]

Yup, it's a 3/8"-16. I got a little concerned when I saw permatex near the outside end of the bolt the previous owner used, and oil towards the end of the bolt inside the head. I can't understand why there would be oil in there, why they'd have to seal it in (that's how it looks to me), or if a stud would make any difference. Sometimes those backyard repair jobs leave the next guy scratching his head!

 

[5-90]

Oil would most likely be from seepage (valve cover gasket leak.)

The "permatex" would probably be blue LocTite - which is all wrong for exhaust hardware. The only thread compound I'll use on exhaust is LocTite #272 - it's formulated for hot environments (like exhaust hardware - that's what it's designed for.)

Considering the heat cycles that exhaust hardware will see, anything steel gets replaced out of hand. Brass or bronze would be annealed (heated to dull red and dropped into cold water, oddly enough) before re-use. Why buy trouble re-using the hardware? You probably get enough for free as it is...

 

[MongoXJ]

You should be able to go by your local auto parts store and pick up a hardware kit for the header that will have new studs and bolts and nuts for everything. I did this when I swapped in my APN, just good practice and makes things much easier.

 

[timba]

I went to the parts store for new radiator hoses (might as well take care of it while it's easy to access - the old ones were starting to swell), so I got new hardware.

Two of the bolts had permatex - I'm pretty sure it's that type of material, and definitely not loctite. It's nearly as big around as the cupped washers that go on the bolts. A few of the bolts looked moist on the end. I like PB Blaster, but I refuse to believe it got that far up the bolt, and the part of the bolt closer to the head was dry. It's a mystery I don't mind leaving unsolved though - this is just my beater jeep and it runs so well I'm afraid to ask too many questions! Thanks a lot for the prompt help, especially since these were my first posts (I've lurked here so long I forgot I'd never posted!). Have a great weekend.
:cheers:

 

[Tim_MN]

I will be doing an APN header soon on a 97 and will be getting new hardware. What did you ask for, a bolt kit? Does it have a part number? Or did you just new bolts that are the correct size?

Thnx

 

[5-90]

I went to the parts store for new radiator hoses (might as well take care of it while it's easy to access - the old ones were starting to swell), so I got new hardware.

Two of the bolts had permatex - I'm pretty sure it's that type of material, and definitely not loctite. It's nearly as big around as the cupped washers that go on the bolts. A few of the bolts looked moist on the end. I like PB Blaster, but I refuse to believe it got that far up the bolt, and the part of the bolt closer to the head was dry. It's a mystery I don't mind leaving unsolved though - this is just my beater jeep and it runs so well I'm afraid to ask too many questions! Thanks a lot for the prompt help, especially since these were my first posts (I've lurked here so long I forgot I'd never posted!). Have a great weekend.
:cheers:

No worries - you learn more when you listen anyhow.

You may have a "weeping" valve cover gasket, so you might want to think about replacing that as well.

And, while you've got it torn to bits, I'd appreciate measurements of most/all of the screws, if you have the means to do so. I'm working on a listing of all the screws used (at least, on the XJ) for reference - just for things like this. I'd need to know:

Year/Engine
Where Used
What Used
Head Style
Thread Pitch and Diameter
Underhead Length (which is how most screws are called out - except for oval heads and flat heads.)

If possible, a picture of the screw in situ would be helpful - I end up making recommendations on what to replace them with, simply because the factory is usually cheap, and hex heads are easiest and cheapest to deal with (but, for instance, I have found that 1/4"-28x1" socket head capscrews are easier to handle on universal joint straps than the OEM 1/4"-28x1" reduced hex head...)

 

[timba]

You'll probably have to talk to Mongo about a bolt kit. I just got 3/8" x 16 grade 8 bolts. If you have a nice jeep, it might be worthwhile buying a bolt set from a dealership. Mine has 201k on the odometer, and supposedly 50k on the motor and trans, so just putting new hardware on may have surprised the old beast.

I used the APN header, and it bolted up beautifully, including the connection to the exhaust. I also followed the advice of one of the many writeups I've found, and cleaned up the threads with a tap. If you want links to some writeups, let me know. It's a pretty smooth job, though cleaning everything takes quite a while.

 

[5-90]

You'll probably have to talk to Mongo about a bolt kit. I just got 3/8" x 16 grade 8 bolts. If you have a nice jeep, it might be worthwhile buying a bolt set from a dealership. Mine has 201k on the odometer, and supposedly 50k on the motor and trans, so just putting new hardware on may have surprised the old beast.

I used the APN header, and it bolted up beautifully, including the connection to the exhaust. I also followed the advice of one of the many writeups I've found, and cleaned up the threads with a tap. If you want links to some writeups, let me know. It's a pretty smooth job, though cleaning everything takes quite a while.

Rather than using a tap, use an old screw and put two or three longwise notches in the threads with a cut-off wheel. Poor man's thread chaser (and it will last you a good long while anyhow.) If you use a tap, you run the risk of cutting a new thread and screwing things up - with the "notched" screw, you just have to remember to back it out and clean the notches.

Replacement hardware is better with brass or bronze - carbon steel hardware should be SAE Grade 5 - not SAE Grade 8. SAE5 is less sensitive to heat cycles, and won't show incremental loss of strength as quickly or as greatly (annealing steel to soften it can be done at temperatures as low as 500*F - I've verified this experimentally at school.)

 

[timba]

I had a discussion about the different grades too. My jeep won't get much use, so I just decided to replace like for like. Then I noticed the originals had tapered ends, and they'd all held up great and came out easily so (don't flame me here), I put the originals back in. This is mostly due to a lack of preparation on my part, and the fact that this is just an old beater.

I think there's a lot of merit in choosing Grade 5, and it's not like there's some huge strength demand in this application. You mention brass and bronze - is this for corrosion? If those aren't available, what do you think about zinc coated?

As for the bolt inventory, pm sent!

 

[5-90]

I had a discussion about the different grades too. My jeep won't get much use, so I just decided to replace like for like. Then I noticed the originals had tapered ends, and they'd all held up great and came out easily so (don't flame me here), I put the originals back in. This is mostly due to a lack of preparation on my part, and the fact that this is just an old beater.

I think there's a lot of merit in choosing Grade 5, and it's not like there's some huge strength demand in this application. You mention brass and bronze - is this for corrosion? If those aren't available, what do you think about zinc coated?

As for the bolt inventory, pm sent!

Brass and bronze are selected because a copper-based alloy won't seize on an iron part (like steel usually does in the presence of heat and close fitment.) Copper also responds to heat in the opposite manner as steel - heat it and gradually cool it, it gets incrementally stronger. And, the transition temperature is a bit higher (which is also strange...)

SAE-graded carbon steel screws are all zinc plated - plain zinc for SAE 5, and usually zinc chromate for SAE 8 (which is where that gold colour comes from.) The thin layer of zinc does not tend to help against screw seizure. (Neither does a black oxide coating - like the OEM screws.)

I do like the pilot points on OEM screws, but they're difficult to find in the aftermarket. They're not strictly necessary in most cases, but they do make it easier to line up the parts when you can't see the hole...

Yes, I've seen SAE8 screws come out after removing an exhaust manifold. That's done for logistical reasons - they use SAE8 damn near everywhere else, and you simplify the logistical train if you don't keep extra grades around (even when using the lower grade is a good idea - like exhausts, or with things like trailer hitches, where you don't want a "dramatic" failure mode...)

 

[ecgtech]

I hope nobody minds me hijacking, but I have a frustrating problem with my exhaust. I just got done replacing the manifold this evening. I used a brand new manifold, new gasket and torqued every bolt to spec. When I started my jeep up, smoked just billowed out from between the header and manifold. Kinda upset that i have to tear everything back out, but if i do i wanna make sure i do it right. Please let me know if there is anything that i need to be doing that Haynes may have omitted from their instructions. Thanks in advance.

ECGTECH

 

[Yucca-Man]

I don't think it's a hijack when the original thread is over a year old.

Did you have clean hands the entire time you were working on the replacement, or did you leave a big greasy handprint on something? Those smoke like mad...

Was the smoke blowing out under pressure from the head and the manifold, or was it a lazy smoke, indicative of burning off grime? Is your fuel rail leaking at all? Look VERY carefully for that, and replace o-rings and/or injectors if it is.

Jim www.yuccaman.com

 

[igotanxj]

They usually smoke from the protective oil layer that was on there. Pretty much every part of exhaust that I have installed in my life smokes like crazy for the first 15 mins or so. Its normal.

But, as was stated, make sure you check for fuel leaks or coolant or oil leaks. Those wont go away after 15 mins!

 

[ecgtech]

I don't think that it is the fuel rail, I checked it over very carefully, replaced all the o-rings and quick disconnects and it was not leaking before i started this project. I am pretty sure that it is leaking at the head/manifold intersection because not only is there smoke BILLOWING from between the new manifold and the head but the noise from the exhaust is much worse than before. I didn't replace the mounting hardware when changed the manifold and have heard that this is necessary. I am going to tear it apart again tomorrow and re-torque everything using new, brass nuts and bolts. Does anybody have any other suggestions?

 

[5-90]

I don't think that it is the fuel rail, I checked it over very carefully, replaced all the o-rings and quick disconnects and it was not leaking before i started this project. I am pretty sure that it is leaking at the head/manifold intersection because not only is there smoke BILLOWING from between the new manifold and the head but the noise from the exhaust is much worse than before. I didn't replace the mounting hardware when changed the manifold and have heard that this is necessary. I am going to tear it apart again tomorrow and re-torque everything using new, brass nuts and bolts. Does anybody have any other suggestions?

1) How much runtime? Typically, it takes a half-hour or so at operating temperature to burn off the worse coating of rust-preventative anything...

2) If you're going to replace hardware, and the gasket is new (<one month, tops,) you can usually get away with not tearing everything to bits - if you replace the hardware one screw at a time! If you use SAE-graded carbon steel hardware (SAE5 is better than SAE8 in this case) or CRES, replace each time you do the job. If you use brass or bronze, it's good for a couple of whiles.

As far as the exhaust noise, you'd be advised to also check the collector flange nuts, and the catalytic converter-to-downpipe flange nuts (if you disturbed those) as well. Just a thought - both of those should turn out to be 3/8"-16 (if SAE) or M8-1.25 (if ISO.)

 

[ecgtech]

5-90,
I'm thinking that the the new leak is at the doughnut flange. i ended up taking everything off again and applying copper-rtv. no more smoke, still a lot of noise that seems to be coming from the doughnut. do i need to torque the bolts in the flange more than Haynes suggests? any help is appreciated since i would rather not tear the manifolds off for a third time.

Thanks,

ECGTECH

 

[5-90]

5-90,
I'm thinking that the the new leak is at the doughnut flange. i ended up taking everything off again and applying copper-rtv. no more smoke, still a lot of noise that seems to be coming from the doughnut. do i need to torque the bolts in the flange more than Haynes suggests? any help is appreciated since i would rather not tear the manifolds off for a third time.

Thanks,

ECGTECH

NO! Part of the reason that installed preload (torque) on exhaust fasteners runs so low is because exhaust flanges and suchlike expand more than just about anything else on the engine (due to elevated heat...) and if you overtorque, you're likely to have something break on you. Not cool!

I've not needed RTV copper on the donut gasket - it usually seals just fine, as long as the flare on the downpipe is clean (no cracks/gouges/burned-in crud/...) It can be done - I just don't see a need to. However, it's not a bad idea on "flat" gaskets - like the combi manifold gasket or the downpipe-converter flange gasket.