Gents,

I am machining 101 stupid, so need advice.

My LEFT side exhaust flange to turbocharger, had a bad female thread in its welded nut.
It is "eating" up bolt male thread and giving false torque value as such, 3-way-CAT flange is not mating and sealing properly yet, the torque wrench already clicking.
The tightening torque is not high, only 20Nm.

This is the part : It is a small piece between turbocharger and 3-way CAT.



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Only one nut is bad. The one I marked red.


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White plastic board is flange surface protection.



Right side bolt is the one being "eaten" by the female nut.
The material used for the baby sized exhaust intermediate flange is very very good.

This baby sized exhaust intermediate flange to exhaust 3-way CAT does not use gasket.
It is like how JIC fitting works. Cone/conver meet concave. High precision metal to metal contact only.


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I can't get thread chaser tool locally. The available one is thread making and repair with insert.
So I have to import from Amazon USA, 4th July it is supposed to arrive in Indonesia.

I bought this one M8 1.25mm pitch
I do not know if this is good enough to make my nut female thread good again ?
China made so it seems and US made ones like Lang also seems to have quality decline.

Any advice appreciated.

Thanks

 

I call that a thread file. I only ever use them for external threads.

For internal threads, I would use a tap to chase the threads. I bet you can get an appropriately sized tap locally, right? Just lightly thread it in to remove the crud, and you should be GTG.

Edit: I thought the cutting surfaces were perpendicular to what they actually are. That looks like a modified tap, so it should also do the trick, but why not just use a tap?

 

I thought for a thread already made, I can't use tap.
https://mechanicalmalarkey.com/2018/...omment-page-1/

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Tap is easy to get.

 

I think you’ll know once you send it through and clean up the threads if you feel there’s enough meat left. Put a bolt in there and see if it wiggles afterwards. If you line it up and get the cut right the first time I think you’ll be fine. Worst case is you go up a size, very worst is doing a through bolt with nut.

Editing to add it doesn’t look like the tool you have is tapered like a traditional tap and I think a tapered tap might make it easier to line everything up. Don’t forget to use some sort of oil or grease depending if you wanna capture the shavings.

 

I tend toward replacing all the bolts when it comes to exhaust work. Older systems use brass or bronze nuts with very little thread left once they come apart. But, they do come apart... Reusing old exhaust fasteners gifts each owner with an opportunity to chase exhaust leaks for the remainder of their ownership. These MB fasteners are probably plated to aid removal. By now, that coating (whatever they used) is compromised.

 

Options:

1. drill out the old thread, tap and install a helicoil or timesert

2. machine the old nut off and use a (new) plain nut.

3. buy a new MB flange

 

Is it dirty with crud, or is the metal distorted? If the former, file a sacrificial bolt to a taper, and then file a notch perpendicular to the threads. Run that down, and it'll clean out all the gunk. If the threads in the flange are damaged, you'll have to reform them. A tap will be the answer, but you're going to want to make sure you get a high quality one. Cheap taps will make the whole thing loose. If the threads are clean, there should be no cutting until you get to the damaged section. Depending on the type of tap you get, it'll either cut through the obstruction, or sort of fold it back where it was supposed to be. Which type you want depends on the damage.

 

I think the thread on the damaged nut should clean well with a thread chaser. You might need a new bolt however.

When I removed those bolts to try to replace the engine mounts (I only tried as I was unable to disconnect the LH side O2 probes...) I've reassembled them with some Permatex’s Anti-Seize Lubricant to help the threads not get damaged as they were pretty tight.

Best!

 

Oky doky allyou guys, thanks so much.
Let me see how the chaser works and if not good enough I will use tap, worse come to worst, weld new nut.

Andre, same here, I can reach the o2 sensor connectors but can't undo them with finger flip....LOL.
My indie has 1 guy with very small hands and he is vefry good with 02 connector removal.

 

Yes. On the RH side I was able to disconnect both O2 sensors from under the car but the LH ones are a pain. I managed to unhook them from the metal clip but they are just to high up on the transmission to get any grip to unplug them. I've studied a bit more about this over the internet and the WIS procedure and found out that MB instructs to disconnect the pre-cat sensors from the top (removing the air box first). I found a post from another forum were a DIYer said he was able to get the connectors disconnected from the top using a long and fin screwdriver. I've looked with the air box removed and the sensor connectors are (barely) visible but this could work, so I got a 3x300 mm screwdriver and I'm waiting for the next Holiday to try again.

 

My indie guy does it 100% from under the car.
First the CAT is disconnected from the turbo output flange and let hang a bit down.
After that he does his magic.
Engine mount replacement need CAT and 50% of exhaust system front side to be removed, thus 02 sensors all 4 must be disconnected too.

Your RH side you can do because your car is LHD and no steering link there and you are probably a right hander too, thus the right hand is better than left hand.

 

try what you bought.
Better to use actual tap with taper on front.

No need for bottom tap or such.
Use cutting oil and go easy back and forth working your way until straight part of tap extends past last nut thread.


My guess is from the high heat the nut warped and is not round anymore kinda egg shape like a Mechanical lock nut. (Class 10 DIN 6927 Top Lock Flange Nut)
which makes for difficult re-use but side effect is that bolt will not loosen on its own.

 

Wow, I did not know there is such a unique lock nut .

The nut probably warped due to heat like how the LEFT ( removed ) exhaust stud has the nut stuck on it and I ended up pulling the stud. Below :



On that baby exhaust flange in discussion , a new bolt when used on the damaged nut .............is already semi frozen by 1st thread.


When new stud and nut arrived for exhaust manifold aka turbo, I will play with it and see how bad is the seizing, is it similiar the exhaust flange nut ?

 

So this is what it looks like when a female nut eats a male bolt? Is that blood?

 

The nut WAS a virgin Jet

 

I blame you. Refoamed an old subwoofer and replaced some trim in my lx that required the rear interior to be removed.




Doh. Seatbelt anchor bolt.

Harbor Freight purchase from years ago

Something for everyone

Tools of the trade

Chasin the thread

Nope nothing wrong here, please move along

 

Sweet , thank you

 

Yipeee, I got a good Japanese made Tap n Die, metric only. by SKC



I will need the M8 x 1.25mm pitch.




US$90 approx with sales tax. Will arrive in 4 days ish and probably the same for the Amazon thread chaser, and I would still be in Bali then.





This SKC company is so old fashion, look at its website ...LOL
http://www.skc-taps.com/english/

 

Okey dokey, I am back in Jakarta and the so called Thread Chaser tool from Amazon USA already waiting for me........

I think the description of this tool being a thread chaser is not too accurate. Thread restoration chaser would be more suitable.





It works VERY well, but I am technically curious. It is more like a Bottom Type Tap



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Very very tiny bit metal cleaned at the female nut. So the Xotic thread chaser tool is not too offensive.

I thought thread chaser woul and should look like below :




But there is another brand which their thread chaser is similar to tap tool, like my Xotic brand.
https://arp-bolts.com/kits/product.php?PL=61






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I failed to get the Japanese made Tap n Die Set by SKC.
The selling company ( Japanese ) emailed me yesterday that stock not available...dugghh.
So I choosen a branded Chinese one instead, DAMN !!!
At least branded and not some unknown no brand product.

I chose this alternative brand :



Their website : https://www.maxpower-tool.com/cuttin...w-tap-set.html

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As long as I got my turbo flange fixed...... I am happy.

 

I recently used this kit to "correct" the caliper hole while working on the rear brakes of my 2000 Ford F-150. (Crazy that that truck uses both metric and SAE sizes throughout.)



https://a.co/d/iAcyd5v

 

So I bought the Lang brand, supposedly still USA Made, metric only thread chaser kit.
I hope today it is still made in USA. 18 July 2025 it will arrive.





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I removed RIGHT side Bank 1 exhaust flange last nite and inspected its female thread.

So this is what happen to these turbos flange.

01. Due to heat, the locked ( not welded ) female nut thread gets kinda "rough". It is not rusty rough. I do not know how to explain it.
One thing for sure, you can never use your fingers alone to screw in the bolt all the way in, you need to use tool......

02. I believe the female nut is of better material than the bolt, thus bolt always lost/damaged.

03. The bolt itself will develop some sort of grey-whitish coating from the heat of service :
See the two top bolts ( from Right side, Bank 1 flange )


3rd bolt from top, with 5-6 damaged male threads, it belongs to the LEFT side Bank 2 turbo exhaust flange and the reason this repair-investigation took place.

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This grey-whitishy coating adds thickness to the thread pitch/diameter, making hand screwing not possible.
If I cleaned off the grey-whitish coating using brass brush and WD-40 equivalent, it will go away, not all but it will smooth the thread.

So I chased all 4 nut female thread on my turbo exhaust flange. 4 new bolts coming soon.
For RIGHT side Bank 1, I left one female thread on purpose to be not totally "chased".
I want to see what will be the difference between fully "chased" female thread and not fully chased one, by next 10,000KM of heat abuse or so.
Fully chased female thread will allow a bolt to be hand screwed easy and all the way 100% penetration. Damn sound so kinky
A not fully chased female thread will need a tool to assist the bolt insertion, but at less than 1 Nm of force, just slight resistance, that is all.


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These 4 bolts on LEFT and RIGHT turbo exhaust flange had been removed at least 3 times since 2014.
Twice is for replacement of both engine mounts in 2018 and 2022 or so.
3rd one is for replacement of propeller shaft middle bearing and rubber boot.
By 3rd removal the bolts I renewed, I was suspecting the bolt was the problem and never thought it was the female thread at the nut.

So now I know what to expect from these nut's female thread distortion overtime with use/heat.
I will be watching them from now on, simply by gauging the effort to screw in a new bolt, that simple.

.

 

These sets are easier to use with a socket wrench so it does make them easier use in many situations. Ive never had a set like pictured above as I find I need a bit more depth and personally like the tapered edge of a tap for alignment of the initial threads. Regardless, all of these tools are excellent to have because bad threads stop the repair process. I clean every exterior thread and bolt I touch on one of the older land cruisers I help maintain that has rust. I think I broke something like five bolts in the frame last time I did a bigger resto job on the subfame and rear crossmembers. I had to drill each one out and then retap. Having the tools on hand made it so I didnt curse...too much.

Op, glad you got this figured out without much fuss.

 

From the Lang Tools website:

"The Lang family has been making tools in Racine, Wisconsin since 1932. We understand professional hand tools - we understand how professionals use their tools.
We are expert toolmakers. From our beginning, A&E has been committed to leading the way in automotive tools. We developed and patented the first Ratcheting Box Wrench, now a standard in every technician's toolbox.
Identifying what the customer needs, and what new tools will help the professional do their job better, faster, and easier has been A&E's hallmark.
At A&E / Lang Tools we take pride in manufacturing the highest quality products. Our customers are professional automotive technicians and industrial end users, along with consumers who demand professional
grade hand tools. They won't settle for anything but the best in their tools, and neither will we. Our family of toolmakers is deeply committed to quality, value, innovation, and most of all, to our customers."

https://www.langtools.com/about-us/

 

@S-Prihadi, knowing how tight that spot is, I have no idea how you removed the exhaust flanges from the top. You must have very nimble fingers

I've took the Sunday off to do engine and transmission mounts. Started the job at 10AM and finished up at 8PM. Finally managed to get my hands around the O2 sensors connectors on the LH side. Had to disassemble a lot of brackets and other stuff that was on they way to marginally get my hand on the connectors. Ended up doing everything from the botton as access from the top was just as difficult. Did the job with the car jack stands on all four corners.

It was a massive pain doing the job preparation (removing the exhaust, crossmember, brackets, flanges, etc.), the rest was pretty easy going despite how tired I was close to the end. I've made holes on the fabric undercarriage protection to access the bolts from the rear crossmember in order to lower the exhaust as I couldn't get it out otherwise. At least like that I've avoided having to remove the entire fabric undercarriage protection from both sides.

Jacked the engine from the corners of the metal oil pan with a floor jack and a large piece of wood to distribute the load. It was interesting that the engine mounts simple felt down when the engine was high enough. Transmission mount was super easy, I've just had to remove the crossmember that is right behind it and jack the transmission from the metal oil pan on it.

I had to remove both exhaust flanges to be able to get my torque wrench in a position to tighten the top bolt from the engine mount. Nice little piece. I think the nuts that you are struggling with are of the high temperature self-locking type (just like exhaust manifold nuts) which means they are slightly oval.

Curiosity - the exhaust nozzle of jet engines get that same whitish coating overtime. It might be a mixture of high temperature and deposits coming from the exhaust gases.

 

Without heat shield of turbo, we get better access. Thus heat shield, 3 pcs, must be first removed.
But coolant pipe-hose ( IN and OUT ) must first be disconnected from turbo if heat shield is to be removed...no fun.






The bronzy heat shield cloth/fiberglass is my own add-on.