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Guess I have to start reading my service reports more closely. Repair tech had to R/R 2 stripped bolts from left Cat. This he discovered while swapping out the tranny. Said they have seen 3 other cars like this recently from the factory like this!
Guess I have to start reading my service reports more closely. Repair tech had to R/R 2 stripped bolts from left Cat. This he discovered while swapping out the tranny. Said they have seen 3 other cars like this recently from the factory like this!
When I did mine I removed those brackets as well and had the left side ones seize. Realized afterwards that the brackets do not need to be removed from the converters. It’s pretty common on GM exhaust hardware. If you look at the bolts the threads aren’t cut fully and they bite into the mating hole.
By chance was yours a HTC?
When I did mine I removed those brackets as well and had the left side ones seize. Realized afterwards that the brackets do not need to be removed from the converters. It’s pretty common on GM exhaust hardware. If you look at the bolts the threads aren’t cut fully and they bite into the mating hole.
By chance was yours a HTC?
I was told this is the left side one too. Forgive my ignorance, but I'm not sure I understand the significance of the thread not being cut to normal depth on those bolts? How does that play into this? My car not an HTC. per my avatar.
I was told this is the left side one too. Forgive my ignorance, but I'm not sure I understand the significance of the thread not being cut to normal depth on those bolts? How does that play into this? My car not an HTC. per my avatar.
I’ve never really asked, my assumption is that it’s to keep the hardware from coming loose due to vibration and the temperature cycling. It’s like that on all our models. Especially closer to the engine. I’ll have to see if I have one I can take a picture for you to see what I’m talking about.
I’ve never really asked, my assumption is that it’s to keep the hardware from coming loose due to vibration and the temperature cycling. It’s like that on all our models. Especially closer to the engine. I’ll have to see if I have one I can take a picture for you to see what I’m talking about.
When I did mine I removed those brackets as well and had the left side ones seize. Realized afterwards that the brackets do not need to be removed from the converters. It’s pretty common on GM exhaust hardware. If you look at the bolts the threads aren’t cut fully and they bite into the mating hole.
By chance was yours a HTC?
That picture looks like the threads are damaged like in a cross thread, too me, but it's possible it's something intentional.
Thread deforming features are definitely common for fastener retention, but I've never seen any that make such a noticeable change to the threads, usually they bite into a portion of the thread that is hard to see with the naked eye, and there's enough thread left that you could reuse the screws. I'll be curious to see what you find out!
You can see a normal thread on top and a typical thread on an exhaust bolt. You can see the exhaust bolt threads aren’t cut fully. The pictures you posted look like they may have been run out and put back in for the picture. The torque on those isn’t that tight and if they stripped like that at the factory their torque tools should have shut down prior to it being clamped. That’s just my mechanic opinion though. Maybe if we have an engineering type they can chime in.
You can see a normal thread on top and a typical thread on an exhaust bolt. You can see the exhaust bolt threads aren’t cut fully. The pictures you posted look like they may have been run out and put back in for the picture. The torque on those isn’t that tight and if they stripped like that at the factory their torque tools should have shut down prior to it being clamped. That’s just my mechanic opinion though. Maybe if we have an engineering type they can chime in.
I understand the reasoning behind the threads not being cut as deep as a standard thread and the thread pitch being different, but it still looks to me like those threads are stripped, especially on the one on the right in my pictures? No?
Last edited by AWSM_06; 06-28-2021 at 09:31 AM.
Reason: clarification
I understand the reasoning behind the threads not being cut as deep as a standard thread and the thread pitch being different, but it still looks to me like those threads are stripped, especially on the one on the right in my pictures? No?
I’m going to guess and say they were pulled out and reinstalled for the picture. Unless you saw it yourself prior to disassembly. They usually thread together without a problem. It’s coming out when that happens.
I’m going to guess and say they were pulled out and reinstalled for the picture. Unless you saw it yourself prior to disassembly. They usually thread together without a problem. It’s coming out when that happens.
I did not witness these pics being taken. They were sent at my request a couple days after I picked up my car. As I allude to in the beginning of the post I read in the service report ( see excerpt) that the tech had replaced stripped bolts and I wanted more detail so they sent me these. Not sure if these were taken of my car or not.
You can see a normal thread on top and a typical thread on an exhaust bolt. You can see the exhaust bolt threads aren’t cut fully. The pictures you posted look like they may have been run out and put back in for the picture. The torque on those isn’t that tight and if they stripped like that at the factory their torque tools should have shut down prior to it being clamped. That’s just my mechanic opinion though. Maybe if we have an engineering type they can chime in.
I don't know if this is the case for these threads but those threads look like they have been rolled.
It is common practice in high strength fasteners to have rolled threads on the male fasteners (look up UNJ threads). This is because the root of the male thread is the weakest point. A sharp cut in the root creates a stress raiser. A rolled thread has greater strength due to a slightly larger root diameter, the process of rolling locally provides more strength, and reduces the stress raiser due to the radius at the root.
A common problem encountered with UNJ fasteners is using a nut that isn't compatible with the increased root diameter. Nuts/holes compatible with UNJ threads have a larger minor diameter to provide clearance for the root on the male thread, usually by using a larger diameter tap drill during fabrication. Otherwise, the crown of the nut can interfere with the root and gall the threads.
You can see a normal thread on top and a typical thread on an exhaust bolt. You can see the exhaust bolt threads aren’t cut fully. The pictures you posted look like they may have been run out and put back in for the picture. The torque on those isn’t that tight and if they stripped like that at the factory their torque tools should have shut down prior to it being clamped. That’s just my mechanic opinion though. Maybe if we have an engineering type they can chime in.
You can definitely see a difference in thread type/class here, but if you look at the photo the OP posted, it looks like there are threads towards the end is the fastener (top of the photo) then down closer to the bracket the threads seem to be missing near the middle of the bolt. Maybe it's just the pics but it definitely looks stripped to me.
When I installed my sport cats I had two of the converter bolts break off on me while removing them. I have plenty of car work experience and was hardly being aggressive. I'm honestly shocked how soft these bolts were. It took barely any effort to snap. I played with them after and they could be bent without any effort. Got to make it start at 60k somehow
This is how my left cat was installed.
Both cat studs are bent due to the uneven bolting.
The hack installing this probably cross threaded the nut on the left because i could not get it off. I fought with it for 30min inching it a ratchet tooth at a time because of the tight access. Finally i got fed up and grabbed the 30" 3/4 ratchet and cranked on it till the stud snapped. The nut was seized on there to where the stud let go before it did.
The right cat has a problem as well because the stud came out instead of the nut. The stud looked stripped/rounded off. Haven checked if that nut was cross threatened l. One of my right studs looked like OPs mangled bolt.
Now i need to replace the studs and nuts on a 6mo old car.
This is how my left cat was installed.
Both cat studs are bent due to the uneven bolting.
The hack installing this probably cross threaded the nut on the left because i could not get it off. I fought with it for 30min inching it a ratchet tooth at a time because of the tight access. Finally i got fed up and grabbed the 30" 3/4 ratchet and cranked on it till the stud snapped. The nut was seized on there to where the stud let go before it did.
The right cat has a problem as well because the stud came out instead of the nut. The stud looked stripped/rounded off. Haven checked if that nut was cross threatened l. One of my right studs looked like OPs mangled bolt.
Now i need to replace the studs and nuts on a 6mo old car.
Can confirm this is a widespread issue on this car. I just went through this on my 2020. They torqued the nuts on way too tight and ended up breaking 3 of the studs. Luckily they still slide out but jesus christ it took an act of god to get some of the nuts off.
I can confirm that the flange side of the studs does not have typical threads. They are either defective or cut to an interference fit.
New studs from the dealer are made the same way.
This is how my left cat was installed.
Both cat studs are bent due to the uneven bolting.
The hack installing this probably cross threaded the nut on the left because i could not get it off. I fought with it for 30min inching it a ratchet tooth at a time because of the tight access. Finally i got fed up and grabbed the 30" 3/4 ratchet and cranked on it till the stud snapped. The nut was seized on there to where the stud let go before it did.
The right cat has a problem as well because the stud came out instead of the nut. The stud looked stripped/rounded off. Haven checked if that nut was cross threatened l. One of my right studs looked like OPs mangled bolt.
Now i need to replace the studs and nuts on a 6mo old car.
By the way I hope, my description of what I see , I've described correctly. or at least well enough for people to see problem.
Looking at the Two studs, they are not installed the same way.
Stud on right side looks to be installed correctly, with the smaller Dia, with the shorter length being on the top side, while the one on the left looks to be installed upside down,
The Studs have a smaller diameter on one, along with larger diameter on the other end.
The stud end with the smaller diameter, should be on the top side, as it also has a shorter threaded length, same way as the stud on the right hand side is installed,
On the righthand side, you can see the number of threads on the smaller threaded end prevents it from having the same flange interference problem as one on the left side, That's at least to me is why the pipe's flange is skewed. instead of being straight. .
Thus you don't get the interference with the stud hitting the pipes flange like it does, as get the same number of threads showing on both sides, no cocked pipe flange.
The stud on the left hand side has an interference problem with the pipes flange, I suspect is due to the big end of stud hitting the pipe's matting flange, cause flange to not seat properly.
If if the Left hand stud had been installed the same same way as the stud on the right, the pipe would have seated correctly,
One thing that bothers me about who installed things wrong, Factory or Dealer, is the color of the flange on the left hand side where it has the interference problem.
You can see where the stud hits the pipe's flange, flange has a bright color to metal where the interference is.
I would expect that metal to be discolored by heat, the same as the rest of pipe's flange.
Based on that, I'd, say it was installed upside-down at the Dealership, not the Factory. .
06-25-2021, 05:05 PM
Stripped converter bolts from the factory!
