Mystery Nut--Anyone Identify?

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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).
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Elle wrote:

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
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Elle wrote:

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".
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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.
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TeGGeR

The Unofficial Honda/Acura FAQ
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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.
http://www.toolsource.com/ost/product.asp?sourceid=googlekd&dept%5FidP0&pf%5Fid 648&mscssid=G130SF55VL6V9K3H98JT1CDLFPKJ5AD9
http://www.bugsandbuggies.com/Parts.asp?CNb6&SNg&GN=9
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Stephen W. Hansen
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Now what do you do for studs that have broken off flush with the head or below?
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TeGGeR

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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.
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Stephen W. Hansen
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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 http://cgi.ebay.com/4-PC-STUD-PULLER-REMOVER-WRENCH-METRIC-SIZES-AUTO_W0QQitemZ4464730279QQcategoryZ50379QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
I also googled on this topic yesterday. The only site that seemed helpful (so far) is http://www.swedishbricks.net/700900FAQ/Exhaust1.html#Exhaust%20Manifold%20Gasket%20&%20Studs%20Replacement . 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.

http://www.toolsource.com/ost/product.asp?sourceid=googlekd&dept%5FidP0&pf%5Fid 648&mscssid=G130SF55VL6V9K3H98JT1CDLFPKJ5AD9
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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.
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nuts from the front suspension. There are 4 identical sized nuts (all 12x1.25 mm) but with different torque settings (page 18-8 of service manual; 1991 Civic). One on top of the strut housing, and two at the bottom, and another one at the end of the control arm. If you need the diagram, do drop a line, and I will scan the page and send it over. Hope this helps......
Elle wrote:

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Is that 12 mm the nominal diamter of the suspension bolts onto which these suspension self-locking nuts fit, though? That sounds more likely.
The 12 mm I mention for this mystery nut is the nut head measurement. That is, a 12 mm socket fits it. The nominal diameter of its corresponding stud appears to be 6 mm or 8 mm. (The stud diameter is a little hard to measure while it's stuck in the nut.)
Thanks for the input. I'll update tomorrow, hopefully.
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Elle wrote:

Most 12 mm nuts on a Honda are threaded for an 8 x 1.25 mm bolt.
Eric
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Hello: I just checked the stud/nut diameters with a caliper after your and Elle's posts. Yes, you two are correct: the 12x1.25 mm that Honda manual refers to is the stud diameter and not the nut diameter (should have remembered this...my apologies). For the 12 mm diameter nut Elle refers to, looks like the corresponding stud size is 8 mmx1.25 mm as Eric correctly suggests. If yours came from the front suspension, there is just one such self-locking-nut according to the front suspension diagram; 8x1.25 mm, stabilizer bar /lower arm attachment. According to the diagram, in the front suspension, there are 6 of 12x1.25 mm self-locking/castle nuts (missed two of these in my earlier post!) 5 of 10x1.25 mm 1 of 8x1.25 mm; all self-locking or castle nuts. As Eric and you indicate correctly, the 12, 10 or 8 referred to in the diagram are for the stud diameter.
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That's what it looks like to me - a high-temperature locking nut.
Mike
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