Mercedes-Benz Forum banner

1 - 8 of 8 Posts

·
Premium Member
2003 SL500, 2012 E350 4Matic P2
Joined
·
840 Posts
It’s about time that I shared my recent experience and my solution to an ongoing problem with our aging W220’s and that is rattling cats. This noise had become such an annoyance that I was embarrassed to have people standing near my car when it was idling and hear that rattle coming from underneath. As you can imagine, the thrill of owning a Mercedes was greatly diminished so I got used to parking away from potential onlookers and not then having to explain why it sounded like a Hoop-Dee.

I had been looking for a solution without having to spend the $500-$800 per side for new down pipes with Cats. I researched and found that some owners had just simple cut the cats out all together and replaced them with straight pipes. Others had removed the exhaust system, separated the pipes and then used a stick or rod to poke and chip the guts out of the Cats. So having seen and read about successful “Cat Delete” ideas, I decided to attempt my own.

I did not want to rely on pipe clamps to hold and seal a straight pipe in place or “break into” the perfectly aligned exhaust system and disassemble then reassemble the system after doing the dirty work. These plans seemed to me to be a recipe for disaster so I decided on the following hybrid method.

Short story on my exhaust system R&I;

The first time I dropped the exhaust system was when I wanted to replace the center support driveshaft bearing thinking that it was the source of a howling noise between 40 and 60 mph. I dropped the exhaust system, replaced the bearing and bracket then reassembled everything only to find that the howl was still there but that I had now acquired a slight vibration at speeds above 70 mph. I didn’t know at the time but there are timing marks on the 2 driveshaft sections that must be aligned to maintain factory balance. I did not mark the sections so I had reassembled them randomly thus out of time.

The second time I dropped the exhaust system was to fix my screw up and remove the driveshaft and have it balanced professionally still not knowing about the factory marking. (I later found out about the markings while following along with and doing research with forum member ricebubbles driveshaft vibration woes.) I got the driveshaft rebalanced with new pilot bushings, installed new flex discs,(my old ones were cracked badly) reassembled everything only to find the vibration now mostly gone but the howling was still there so…………

The third and final time that I dropped the exhaust was to replace the rear differential. My detailed story is in the following post:
http://www.benzworld.org/forums/w220-s-class/1728601-whiny-noise-rear-finally-solved.html

It is at this point that I will go through the gruesome and graphic details of gutting a cat.

First some preliminary temp checks with car fully warmed up to determine materials needed to withstand the heat;

Forward Cats:


Rear Cats;




Okay, we now have several test samples to establish a base line. It looks like 311 deg f max on one sample.

Next, exhaust system on the floor (dropped during differential change out project).


Inspect both Cats and look for the flattest surface to install a cover plate to cover the proposed clean out hole. Looks like upper quadrant is the best. These are odd shaped assemblies.

File welding splatter to check flatness, this area should be flat enough to seal:

Now for the parts that I used:

650 deg F RTV sealant for added sealing if needed………………

High temp exhaust manifold gasket material:

Sheet metal screws to secure the cover plates:

I used some scrap .062” (1.5mm) sheet metal for the cover plates:

And finally, some High Temp Gold paint to pretty it up at the end:

Cut two templates out of cardboard, one for the cover plate and one for the cleanout hole:

Trace cleanout hole template onto Cats with marker. You can just make out the Cover plate traced in pencil.

Drill holes to saw into............

First saw cuts: I used a hand held electric jig saw which worked great.

Second saw cuts, (no turning back now) you are looking at the guts of this Cat, Passenger side………..

And now let the gutting begin,(are you squeamish yet??)

and continues..........

Finally, success..........



Now, on to the driver’s side, drill and saw. This is the side that was rattling. The guts/honeycomb are able to move back and forth freely. Notice too that half of the innards are missing! My thinking is that this Cat was assembled and welded shut exactly as you see it here, with half of the honeycomb missing. A Factory defect missed by the inspectors before it was jig welded to the rest of the pipes. Compare this to the previous passenger side Cat which was fully packed.


Honeycomb was floating back and forth freely..........

Okay, both sides gutted and ready for sealing back up.......


Continued in Cat gutting part two. Hopefully Warren can append these posts together for continuity.
 

·
Premium Member
2003 SL500, 2012 E350 4Matic P2
Joined
·
840 Posts
Discussion Starter #2
Cat gutting part two

This is a continuation of the first post. I ran out of space allowed.

But first, use the shop vac for a good vacuum..........


Then a thorough inspection for any errant Cat guts………….



I cut the cover plates and gasket material, laid out the hole locations then clamped them together on the bench and drilled them as an assembly…..

I carefully began the process of drilling pilot holes in the Cat and fastening the cover plate & gasket one sheet metal screw at a time.……

and two more.......

Now the rest..............


I did exactly the same procedure on the other side so no need for more pictures. I do want to point out to the other mechanics following along that I used plenty of screws by design as you can see , overkill perhaps but I did not want to chance even the slightest leak to spoil my handiwork. Not only that, this was not the flattest surface to work with so I wanted to pull everything as tightly together as possible…………..

I masked off the area with tape and applied the High Temp RTV around the perimeter of the cover plate and gasket about .25” (6mm) overlap. I removed the masking tape the next morning to expose a nice clean edge……



And now to pretty it up with High Temp Gold paint, (matches the original system color pretty good)……..




Okay, this completes the Cat gutting. (You can put away the Barf bags now) At this point, the rest of the job is to just roll the exhaust system back under the car and install it back up normally.

I took a couple of pictures when everything was back up and secured properly. If you look closely, you can see just a hint of the Red RTV bleeding through the Gold paint. I’m not sure if you can even paint RTV. It will probably flake off over time………..

Right side…….


Left side............

and bottom............


To the untrained eye, there is nothing unusual about my exhaust system and it should be able to pass any visual inspection check easily. Just some inspection plates on top as usual right?? :)

A word of caution, when I was breaking up the honey comb with a hammer and screw driver on the passenger side Cat I got a little careless with some of my hammer blows and darn near created a real problem on the bottom of that Cat. Good thing that they used heavy gauge construction on the Cat chambers which will outlast the body sheet metal hands down.

Notice the dimples…………



Finally to wrap up, this is a pretty straight forward job just time consuming and somewhat tedious but very do-able for the average DIYer. Be careful to keep track of the pieces that you chip out of the cat so as to not get them lost in the pipes in either direction of the Cat. I stuffed a rag into the pipes as soon as I could to keep the mess confined to the big chamber. I used a mirror and flashlight (torch) to be certain that I had everything out of the pipes before sealing the Cat chamber back up. I also relied on my shop vac to clean up inside the Cats as well as the mess surrounding them.

The car runs no different than before except no more embarrassing rattle. The exhaust sound has not changed to my ears and is still very quite. There are so many noise dampening components in the exhaust system anyway that having this little amount removed shouldn’t make a difference.

I guess now that I have uploaded this for all to see, I will have to head for the bunker in my backyard and lay low. I wonder, does anyone know if the EPA uses drones??
 

·
Premium Member
'02' S500 (W220)
Joined
·
586 Posts
You are Caught! I am with the EPA (Equipment Performing Association) and you modified a very precise and expensive audibly tuned piece of equipment with dynamic rattle features. Forget the drone, a skud has been launched in your direction! Should be there in a week or two.
Well done my friend! That is truly thinking out of the box or Cat should I say. I have that same rattle and my next project was to drop the exhaust for r&r of Cats. I wonder however if this would affect the o2 sensors thus causing error codes when State Insp. is due? I like this approach however as it is certainly "cost effective".
 

·
Premium Member
2003 SL500, 2012 E350 4Matic P2
Joined
·
840 Posts
Discussion Starter #4 (Edited)
Thanks for the warning Brother Deucer,

I shall put my wetted finger up into the air to try and anticipate the direction of the arrival of the Scuds.

Not to worry on the CEL. The O2 sensors are forward of the rear Cats so not a factor:




There is a exhaust removal Pdf file attached to my differential writeup. I truly hate dropping the exhaust although it is relatively easy. I am always worried about not getting the pipes seated and aligned on the exhaust manifold but so far, it has not been an issue. I am careful to get the pipe clamping flange on straight.
 

·
Banned
2003 Mercedes S430
Joined
·
806 Posts
What you did is not only illegal, a Federal offense, but you exposed yourself to highly toxic media that is a known cancer causing agent.

You have this dust in your lungs now. How very creative.

Enjoy your savings. For me, I would have replaced the cats with new pipes.
 

·
Registered
1997 SL600
Joined
·
16 Posts
What you did is not only illegal, a Federal offense, but you exposed yourself to highly toxic media that is a known cancer causing agent.

You have this dust in your lungs now. How very creative.

Enjoy your savings. For me, I would have replaced the cats with new pipes.
From my studies of the EPA and no one cats is that if you live in a area requiring the cat it has to be inplace,
What you did is not only illegal, a Federal offense, but you exposed yourself to highly toxic media that is a known cancer causing agent.

You have this dust in your lungs now. How very creative.

Enjoy your savings. For me, I would have replaced the cats with new pipes, if the housing is inplace ? Do you know that it is a proven Fact that a vehicle Without a cat puts out much lower emissions than one with the cats in place so why shouldn't everyone make a positive impact on our environment ?
 

·
Registered
1989 W124 260E
Joined
·
1,275 Posts
Dont know how your country checks out these exhaust gas emissions tests , but this job allthough one of the best i have seen. Might cost you in the end and you migh have to replace those cats to get it through the smog test i dont know if the smog test comes in to the mot test your region But .in the uk drivers have took their cars for the yearly mot test only to be told your car came from the factory with catslooking at your vin number so there for must be fitted for the mot pass .
 

·
W220 Moderator
Joined
·
6,040 Posts
In UK anything post 1991 had Cat's.

Actually, (and I'm not trying to insult the OP or be picky), buuuuuut, I just gotta say what I see ..........

I think that is an awful job on 2 counts ...............

1) If you are going to do it, the "Proper" way is to cut all the way around the weld, take the brick out and put a suitable diameter pipe in before Welding the end back on, then it will pass any visual inspection and also won't create Exhaust Gas resonance and upset the flow ;)

2) He claims that Cat came from MB with a broken Brick ........................ Utter Tosh !!
That is exactly what happens when they start to break up, and he didn't get the broken bits out of the middle Silencer either, which is is exactly where they will be lodged, obstructing the Exhaust Gas flow ;)

Not to mention that a Cat in decent condition is a legal requirement :rolleyes:

Ho Hum .........
 
1 - 8 of 8 Posts
Top