Mystery Nut--Anyone Identify?

Broken studs are very common. I had one too. Mine broke below the surface
of the head. My mechanic removed it, but wouldn't tell me how (trade
secret, or so he says...). It was done at the same time as my head gasket
replacement, so the machine shop that trued the head probably did it.

The problem is that exhaust pulses are quite violent. This is the reason
you need heat-resistant "prevailing torque" nuts. The nuts don't vibrate
off, but the pulses often break a stud.

Funny, the one that broke on mine was the one nearest the timing belt. It
must be a random thing.

 

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

 

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

 

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.

 

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.

 

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??

 

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).

 

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

 

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".

 

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".

 

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.

 

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.




http://www.toolsource.com/ost/product.asp?sourceid=googlekd&dept%5Fid=500&pf%5Fid=98648&mscssid=G130SF55VL6V9K3H98JT1CDLFPKJ5AD9


http://www.bugsandbuggies.com/Parts.asp?CN=626&SN=67&GN=9

--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Automobile Advanced Engine Performance
ASE Undercar Specialist

http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm
http://www.troublecodes.net/technical/
http://www.familycar.com/Alignment.htm

 

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%5Fid=500&pf%5Fid=98648&mscssid=G130SF55VL6V9K3H98JT1CDLFPKJ5AD9


http://www.bugsandbuggies.com/Parts.asp?CN=626&SN=67&GN=9

--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Automobile Advanced Engine Performance
ASE Undercar Specialist

http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm
http://www.troublecodes.net/technical/
http://www.familycar.com/Alignment.htm

 

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