No real need to bring this topic/my dilemma back to the top; but I didn't want to leave this thread hangin' (so to speak)...

In an effort to rule out what might be contributing to the obnoxious exhaust rattle - The other day I replaced the lower engine mount.
The previous mount had a little over 8k (w/powerflex small bushing), since I'd replaced it late last fall. Upon removal and inspection it looked fine. The larger end (w/out powerflex) appeared firm with no splits or tear.
From my experience; I've never seen or had the large end of a lower mount go bad. It had seemed to always be the small end rubber that eventually fails/degrades.
I transferred the smaller end powerflex bushing on to the new mount and decided to add and install a powerflex insert into the large end for good measure.




To cut to the chase - Installing a new lower mount upgraded with powerflex bushings, made little difference and did not seem to be related to the rattling noise.
It has to be something else.

Not much room to work under my Mini in a parking lot; Although, for my own reference; I attempted to take some photos.








During my inspection and installation of the lower mount, While the car was running and the rattle noise was present; the sound seemed to be coming from everywhere down the length of the exhaust pipe.
But the exhaust was steady as a rock with very very little vibration. Noise travels...So I moved up and down the length of the exhaust pressing and holding each section until I came upon the CAT.
While applying slight pressure to the cylindrical body of the catalytic converter, the rattle seemed to diminish or stop. Although there is/are absolutely no visible sighs of a crack or break in the CAT, not coming in contact with the body or heat shield, no movement at either end of pipe, I am leaning to believing that the barrel of the CAT may have somehow become separated within the area I've indicated above with red arrows (?).

Interesting to also note; that the vibrating rattle noise is most obstreperous when the car is first started (cold). After warm up and under normal operating temperature and while driving - the noise subsides and the exhaust sounds almost normal with nary the slightest bit of rattle.
The rattle returns when at stopped or idle.

 

I am sorry to hear that you’ve landed on the cat as the cause of the noise. I had hoped that would not be the case, though from your description it seems just like my problem.

Here are two pics of my cat, which to me looks like it has a crack. It’s tough to tell shadow from crack, however.

 

That is a press fit. It’s BS. There is a thread about getting it welded. I read that, and had mine welded. Solved a random misfire. I had it done at a shop - never took it out. Done in place.

found it

https://www.northamericanmotoring.com/forums/stock-problems-issues/210497-cracked-exhaust-manifold.html

 

Thanks for the latest replies!
After determining and coming to the conclusion on my own that the CAT had separated (in wich I almost refuse to believe it could happen to me) - I thank you for digging up that thread. It is also benificial to note that this kind of failure at the cat is not uncommon with our cars but can be remedied by welding it back together.
I'm still fairly new to these parts since having landed here just a few months ago; but hopefully can find a muffler shop out here that will be willing to do the repair.
Thanks!

​​​​​​

 

With the notion of possibly having the cat welded; I stopped into a commercial muffler shop/garage up here in midtown ABQ to inquire about welding the cat on my Mini. They wouldn't weld it with the cat still mounted to the car.
R&R-ing the exhaust, welding the CAT, new gaskets = $600 with no guarantee that the rattle would be eliminated.
Shopping around, I headed out to the SW valley that I affectionately refer to as "Auto Heaven" or "Detonation Boulevard" = A 3mi long industrial area lined with nothing but salvage yards. There I found a small independent that would weld the cat for $200 or sell me a used
one and scab/weld it in for $400.

Alright - either way this thing is going to cost me $$....And I'm not even certain that it is the CAT that's broken.
I don't know if it is so much the cost as it is as my Mini is my daily and they would need the car for a day or two.

Someone suggested to me that they had great results with JB Weld Extreme Heat paste and exhaust wrap in fixing/mending a crack between exhaust pipe and muffler.


FAIL : After applying JB Weld Extreme Heat into the seam area on both sides of the CAT and letting it cure for 16 hours -
Yet the results were disappointing. Not due to the JB Weld product itself but due to my continued failure to pin down the EXACT source/cause of he rattle.

My next thought was to try to isolate the vibration by means of restricting movement. In this case; I used a couple of small pieces of wood.


FAIL : This was a bad idea. The pipe did not like being pressed against the chassis an responded violently shaking the car.


ALMOST success - A block of wood wedged against one side of the CAT reduced the rattle significantly. Whilst two,resulted in too much restriction and increased the rattle even more so into the chassis.

Ok - So if the above large cylindrical thing is the "CAT": What the heck is this thing (in pic below) and what is it referred to? - the "pre-CAT"? or "manifold"?...


Regardless; Now that I reflect on my previous failed attempts, perhaps this is the culprit that needs to be addressed/welded or at the very least where I should have applied the JB Weld Extreme Heat putty in my first attempt.
Might be a good thing that I hadn't. If I had - it might impede welding if this is the case.

In the meantime; I'm moving forward to replace the upper engine mount. I have a brand new one in my new back-up parts.
Although from my perception, the engine does not vibrate enough with the existing one with less than 10k mi currently installed in my Mini.
But something had to cause enough vibration for "whatever it is" to come loose.

 

those prices are crazy for the welding. you shouldn't get hit for more than $100 for a weld job like that. did you try to find a corner combo muffler/used tire shop? that's where i'd start.

of course, it never hurts to own a welder. you don't have to lay down professional quality dimes just to melt two pieces of metal. heck, muffler shop welds don't look great but they hold.

i have too much pride to show how it looked when i was done, but i was able to weld up this crack good enough to hold on a used catback from the junk yard.

 

Yes - I consulted Midas and a "corner" auto/tire/ muffler shop in midtown. Midas wouldn't weld it. The auto muffler shop wanted too much and I wasn't too keen on them working on my Mini.
That is why I headed down to the valley. The valley is all about cars down there. Plenty of independent gearhead garages down there.
​​​​​​And yes - I finally had to donate my MIG (along with about $6k worth of industrial equipment ) to Goodwill before hitting the road (moving + no room in my Mini) out here. 'Had that MIG for forty years.- it has definitely seen a fair share of custom headers and exhausts (andthensome), I've welded up during that time.

 

That's heartbreaking to hear, but sometimes you gotta go what you gotta do, I guess.

 

Yeah, you said it - and that's not nearly as heartbreaking as all the good/excellent, 1st Gen Mini parts $$ I've collected over the past 10 years that I had to give up.

 

The shop that did mine is not near you, but yes, it was done in the car. I paid $125? This was 18 months ago.

 

I'm thinking I am going to have to "close the book" with regards to this phase of my exhaust rattle issue.
I managed to negotiate the price down with the guys at the SW valley indie garage to welding the pre or CAT for $100. As I'd hoped - I finally got this car up on a lift. They didn’t even have to do a thing. It took about 3 seconds up on the lift for them to figure it out....

The good and bad news:
The Good:
There is nothing that needs to be welded.
The Bad:
There is nothing that needs to be welded. The issue (as I'd considered early on); the problem is internal = the inside of the CAT has broken loose and is rattling around inside the canister.

2wo options to consider:
1) Replace the CAT
2) Cut open the CAT (canister) and gut it
Or, the third option:
3) Go CATless and just hope I don't wind up moving to a state that has stringent emissions laws.

Btw: These guys at the indie garage didn't charge me a dime.
I brought them a 12pack of Modelo and thanked thttem again an hour later.

And, if you're at all curious; JB Weld Extreme Heat holds up pretty well under 1,000 continuous degrees.

 

Even if you buy a cat that is not OE mini - get a new / another cat. The car needs and expects that to be there. Open loop does not work with these cars.

 

could be wrong, but my understanding is that the pre cat o2 sensor holds closed loop

post cat sensor is simply a test for a functioning cat. purely emissions related

 

Interesting.
I often wondered how some of those guys run CATless with performance exhausts without any issues?.
I'll be looking at buying a new Cat rather than going to a performance exhaust.

 

It will run. Anyone who says it runs better, is likely lying. I’ve been around cats since 1981 - yes, I am old. It works. Also, that cat/header is one piece from the exhaust ports to the intermediate pipe.

 

what i'm sayin is. post cat has nothing to do with closed loop or performance. zero.

post cat will give you a check engine light, but thats just for the law makers