Mystery Nut--Anyone Identify?

"TeGGeR®" wrote in news:Xns97C8D2ABBFBEtegger@207.14.116.130:

That combined with the exhaust system flexing as the engine torques on its mounts, of course...

"TeGGeR®" wrote

Mine is broken off at the outer surface of the exhaust manifold. Hopefully "all" I have to do is remove the manifold, and I'll plenty of leftover stud to drill/double-nut/etc.

I'm not going to pursue it until I get my new front lower control arm bushings in (knock on wood). Tomorrow's a big day.

Doggone Napa said they had the stud. I go there and they insist it's a 10 mm stud. I didn't have the broken nut-stud with me and bought it. Back I go.

Interesting. Maybe I'll see about replacing all nine or so, before they break within the cylinder head.

Thanks for the info. As always, it's very helpful.

What torque should be applied to the exhaust manifold stud (91 Civic LX, 176k miles) when installing it in the cylinder head? This torque specification does not seem to appear in the service manual or my Chilton's.

I see the locking nuts get 23 ft-lbs, so I suppose that's reasonable for the studs, too. Still, perhaps someone here has some more insight or thoughts on what is reasonable here.

Also, ISTM I should replace all nine studs. Any good reason not to? "If it ain't broke, don't fix it," is a good rule, but on a car this old, and since broken exhaust manifold studs are fairly common, I think an ounce of prevention may be appropriate here. Your experience on this matter is welcome.

I plan to double nut the studs to remove them, being mindful that they are fatigued and could very well break off in an undesirable way.

Again, they're 8 mm nominal diameter studs.

My Civic yesterday recorded the lowest gas mileage since I started keeping careful records two years ago--36.3 mpg vs. my average of about 40 mpg (higher in late spring and summer). It's never been this low for this time of year. I googled and it certainly seems that the missing nut may be causing an exhaust leak and causing the engine control system to run rich.

I am pricing a new exhaust manifold gasket, studs, and nuts locally today.

Studs should have slightly more torque than nuts as it is desired that the nut turn freely (when loosening) while the stud remains in place. this can be done by locking two nuts together when installing the stud. Using "lock tight" is also a possibility but may not be as effective due to the high heat this application must endure.

Yes, I would replace all of 'em if it is not a big hassle.

That's ok. Just be patient and work the studs in both directions to gradually loosen 'em up. Also, a direct blow or two to the top of the stud itself can be beneficial. Just make sure a nut is present to protect the threads.

Ethanol mix maybe??

Sounds good. My parts are on order locally and I think I'll work on this before my pass. side front bushings. I'm going to soak as much as I can of the applicable bolt threads in PB Blaster today. Fortunately I had the header pipe disconnected from the exhaust manifold a couple of years ago.

Thanks for sharing your experience, JT.

No. I am using the same gas stations I usually use. They haven't shifted. Last time I did get a winter mix, I didn't notice a change in fuel mileage (using odometer miles/gallons added to top off).

I think that all gasoline sold nationally now has to have an ethanol content of 10% that replaces MBTE (sp?) that was declared "dangerous" by the EPA.. There was a big fuss by the oil companies and refiners.

JT

AFAIK, they basically just thread all the way (half way?) in, and thats it. no torque necessary. when you attach the nut and washer, and torque

*that* it tightens the stud as well, or at least causes the stud to become "elastic".

SoCalMike wrote in news: snipped-for-privacy@comcast.com:

I suspect you're right. Just tighten until it bottoms, then stop.

I just checked several factory manuals here, and not one specifies a torque figure for the studs.

Elle, I have 2 4 piece sets of these (the picture doesn't show the bottom) It has

3 cams that roll out and pinch the stud for removal and installation. It sometime leaves small dimples in the stud but has never effected the operation. Check Sears, Harbor freight. Saves tones of time on studs. (i.e., threading two nuts on, having them slip, re tighten, remove stud now try to remove the nuts for the next go-around.

"Stephen H" wrote in news:RnScg.92413$ snipped-for-privacy@bgtnsc05-news.ops.worldnet.att.net:

Now what do you do for studs that have broken off flush with the head or below?

Stephen H, wow, thanks! I'll be checking around for these locally "stud removal sockets." I just checked Ebay and found a few (and just a few) similar kits. For others who are interested, the bottom of one such set is partly shown at

I also googled on this topic yesterday. The only site that seemed helpful (so far) is There is indeed a mention of a "locking collar type stud remover." On first reading, that went right by me. It's surely the tool you suggest, though.

Tegger, for studs that are broken off flush with the cylinder head, several folks at this site make a strong argument (based in experience) for right angle (and reversible) drills.

Aside: I was at Harbor Freight yesterday. Fifteen dollars buys a lot of tools which show, to me, great promise for making my bushing replacement efforts easier when I go at the passenger side lower control arm in a day or so. Air hammer (seven bucks), tiny 3/4-inch diameter diamond mini cutting discs (for my air die grinder), tiny wire brush for a low RPM electric drill. I'm frugal, but I kept thinking, for two or so bucks more, this or that might save me five hours and a lot of sore muscles, keep me safer, etc.

I go at the exhaust manifold studs maybe next week.

"Stephen H" wrote

I use drills; heat and easy outs Drill it open, insert the easy our and try; sometimes the heat of the drill breaks it loose, but be careful, you don't want to break the easy out. If that doesn't do the trick, an ox/ace torch, heat the stud hot and then try.

Per Stephen H.'s suggestion, I bought an 8 mm stud removal socket (with the roller cams) on Ebay for $13 ($7 + $6 shipping). Over the past two weeks, and after driving the car awhile so the engine was hot, I removed the old nuts and applied PB Blaster so as to maybe penetrate to the studs' threads. The stud removal socket worked perfectly on all nine studs, including the one partly broken off. Enough stub was left so that it was not a problem.

Very little torque was required to remove the studs with the socket. I needed only an ordinary 8-inch ratchet with a little pressure applied. It seemed they might have still been tightened to the 23 ft-lbs specification applied at the factory some 15 years ago! The old studs were very clean, and all threads were in good shape. Nonetheless since they were surely fatigued from cyclic heating and cooling and vibrations, I replaced both studs and nuts.

The original exhaust manifold gasket is a three-layered, aluminum like affair, with the layer nearest the engine having webs. The new gasket I bought is a single layer, no webs. Dunno what's up with this. I retained the first two layers and replaced the layer furthest from the engine, since it looked most like the new gasket.

The three manifold-to-header-pipe stud threads are in questionable shape at this time, from the two times now I've applied serious torque. I'll chase them down soon and possibly replace them.

Fortunately th was a very easy job.

Test drive was fine. With every control arm bushing set I replace, I think the handling is improving. I think it is worth the effort I am putting into it.

Little aside: I previously reported a seeming drop in fuel mileage (to 36.3 mpg, a record low in the last few years) after the one exhaust manifold stud broke. On the next tank, the fuel mileage shot up to 47.8 mpg (a record high in the last few years). So I think something was screwy during my last two fill-ups. The average is close to my usual average for this time of year.

I remain much obliged to people's input here. It's great to learn and build, literally.