Advice for stripped threads upstream oxygen sensor exhaust manifold

IF it were my car and IF the manifold is steel, I would remove the manifold, then remove the square nut, and weld or braze in a thin-ish nut of appropriate thread size. If no thin-ish nut is available then make one with the dremel. The sensor needs to be in the flame and also have good thermal conductivity to the manifold.

Back to your friendly Loctite dealer for the Form-A-Thread kit? Trip to a junkyard for a new manifold if replacing it isn't too painful? Helicoils?

I had not thought of putting a new nut on. I'll look in the morning to see if the nut is the only threads. I'm sure the sensor has to be "in" the stream of hot vapors.

It seems to be cast iron. Aren't they all that way? (It's rusty.)

I guess it can't hurt. I can contact Denso to figure out the thread pitch for their O2 sensors.

I was thinking of cleaning up the threads, but they look really bad. How on earth can ANYONE do that to a bunch of threads?

What did they do? It's not even hard to get to ... it's right there ... in front.

Seems to me the choices are... a. New or used manifold (if it's not too hard to replace) b. Drill it out and helicoil it (nothing to lose really) c. Clean it up with a tap (I don't have the tap, which won't be cheap) d. Shove it in there with epoxy (I hate that idea so I don't want to)

Thanks for confirming it's the same threads as a spark plug, which, at the moment, seem to be 18x1.5 for them.

Googling, it seems cast iron isn't easy to weld, and that the plug rethread might work, but, the heat cycling has likely hardened the bung nut, such that it's a LOT harder (some say) to deal with than a spark plug thread which is typically in aluminum engine blocks (they say).

Searching for this "plug rethread kit", is this the $62 kit you speak of?

That metal paste is anti-seize compound. Use a thread chaser before installing the new sensor.

replying to Arlen Holder, fozz89 wrote: You could try and tap. (cant see your pictures BTW) It depends on how much material is missing from the original threads. I dont know my way around Jap cars too well but usually with the right equipment you can just flash the PCM and make emissions BS go away permanently (along with your catalytic converter) More HPs, Better mileage, more crying liberals.

The helicoil route won't be cheap either. The epoxy route is redneck engineering at its finest but this is a 14 year old beater, right?

As an aside, general purpose epoxy isn't a good idea for an exhaust manifold.

There's a reason I didn't respond to that suggestion of removing emissions. There is absolutely zero chance we are going to mess with the emissions. Zero.

It's going to be street legal smogable or we won't do it.

You have it out, measure the pitch. The helicoil is probably the easiest solution and I am generally a fan of the things.

They tried to remove a stuck oxygen sensor cold, maybe without even using a proper penetrating oil, and they just put force on it until it deformed and eventually tore itself out.

Are you absolutely sure it's the problem also?

--scott

From research since yesterday, all oxygen sensors seem to be M18x1.5 so I'm clear on that.

Thanks. I think my current plan is: a. Pick up a thread chaser & try that b. If that can'd be found, consider a junkyard exhaust manifold c. If that fails, consider a new one d. If that's too pricey, consider a helicoil kit (but they're pricey too) e. Maybe even consider drilling and then inserting a threaded bung

Jesus. Who would do that. I have never stripped a thread coming out! (I've stripped threads going in, but never coming out.)

It is now. :)

Plug threads are M18 x 1.5 or M14 x 1.25 on most automobiles. The M18 are the older plugs and O2 sensors and the M14 are the common peanut plugs used these days.

Heat cycling will have made the iron harder to work with but the tools used are designed to handle that.

That kit would work but I like using a solid insert myself, they hold up better. I use timesert myself.

If you check with many of the chain parts stores they may have a thread repair kit as a "loaner tool". You "rent" the tool use it, return it in good shape and get your money back. You pay for the insert(s) you use. A lot cheaper than buying the kit for a one time repair.

 *NO*!! That kit uses standard helicoil inserts , which are fine if you're using spark plugs that use a crush washer to seal .  What you want is similar to one I have and have used , mine is a NAPA auto parts #770-3223 "Sav-A-Thread" kit  - it's for 14 mm plugs but you need the one for 18mm plugs . For the heat cycle hardened threaded bung you need to heat it red hot with a torch and let it cool slowly - even if (and it has) the steel has absorbed carbon from the exhaust gasses the slow cool will anneal the metal (will help a great deal if the manifold is hot too ...) . If you can cut it with a file , this kit will work . One suggestion - drill the hole out enough to clean up the old threads plus a bit , it makes the ream/tap operation much easier . This kit includes a punch that upsets the top edge of the insert (solid metal insert) knurling into the threads to keep it from backing out . This kit is made by helicoil , you may be able to find it at another retailer - I bought another from O'Reilly Auto Parts because this one was "lost" in the move when I left Memphis for rural Arkansas .  I've used these kits twice , in 2 different vehicles with excellent results . Both were "hemi" type OHC motors with the spark plug straight down the center of the valve covers . Both required machining guide bushings to be sure I got the hole straight (I have a machine shop , it's a "hobby") and both have run for many thousands of miles trouble-free . Good luck !

I went to O'Reilly's and Autozone today, where the loaner tap and die kit at O'Reilly doesn't come close to the M18x1.5 needed here but they do sell the M14x1.25 thread chaser for those smaller spark plugs:

I bought from Autozone this M18x1.5 thread chaser and will get the kid to work with me in a couple of hours before nightfall and report back.

I understand that a used exhaust manifold is problematic.

Worse, it appears that the catalytic converter is integral with the exhaust manifold on this vehicle, so, getting a "used" cat is problematic to start with.

Thanks for that advice based on your experience, since I have zero experience with these things.

I saw that kit at O'Reilly's which I photographed on their counter.

The sort of good news is that the thread chaser bottomed out entirely by hand, without any strength required whatsoever, but the sort of bad news is that it didn't clean up much as a result:

Still, at least that "jb weld" or "epoxy" or whatever it was, seems to be cleaned out.

The thread chaser really didn't clean up the threads as much as it pushed out the jb-weld-expoxy-whatever stuff from the valleys.

This is California, so, if there's anywhere on earth that you're not allowed to do something, it's gonna be in California for sure.

So that knocks out a used exhaust manifold from the equation.

BTW, I think I figured out WHY the ham-fisted person cross-threaded the old oxygen sensor.

The radiator upper hose is in the way of a straight shot, so I gently removed the upper radiator hose (which was rather loose with a hose clamp).

Then I was able to get a perfectly straight shot on the thread chaser:

Hi Clare, You've always been right, over the years, on everything!

I will always strive to take your advice, as you have the experience I lack.

I did clean out the threads late this afternoon just before nightfall:

After removing the upper radiator hose to get a straight shot and hand threading the oxygen sensor thread chaser a few times up and down into the hole, I hand tightened the new oxygen sensor (which came with a crush gasket like spark plugs do) into the threaded bung.

When it met a slight resistance, I used the crows foot, still by hand:

Then, when it bottomed, I gently applied leverage ever so slightly:

I figured it would be better loose than too tight, as I didn't want to risk the threads, but I did snug it down with, oh, about 20 foot pounds in the last 1/8 turn or so. Then I transferred the old metal bracket to the new oxygen sensor:

And I buttoned back up the heat shield & routed the oxygen sensor wiring: