jwbeck17

I got the Belmetric cap nuts M14 x 1.5 size and they fit perfectly. They also are not too bad to look at...

jwbeck17

That leaves me to do the bellhousing inspection for possible loose bits. Any suggestions on how bet to do that on a manual?

jwbeck17

Update...I was able to do an inspection within the lower bellhousing, including the front and back pinch bolts. The pinch bolts were tight, but I believe Stan touched them last so not surprised. (I found a VERY helpful video of Stan showing pinch bolt checks from last year's Frenzy that was helpful!) I checked pressure plate bolts and any other bolts for looseness, but all seemed to be solid. I decided to blow out the area with some compressed air followed by brake cleaner to get any little bits of dust and dirt out and sealed it back up. I also blew some air around the exhaust shields and tight areas just in case there was some junk there. In my inspection I did find a heat shield missing a screw, so I replaced it.

I haven't had a chance to test it yet apart from firing it up and checking clutch engagement (to make sure I didnt screw anything up). If I test and the noise is still there, I think i must be looking in the wrong place and am back to hunting it down. (It does not sound like a bearing issue or a grinding.) However, it was good for me to do some inspection down there to increase my knowledge and comfort with the car.

Will report back with any pertinent details.

Jason

jwbeck17

I'm bringing this thread back as I have an update and welcome some suggestions.

While I was unable to stop the rattling with bellhousing inspection and the test port recapping, I was able to figure out a way to identify the location of the rattle, and thankfully this is a simple one.

Basically I sat on the ground by the driver's side with one stick pushing on the throttle gently and another stick putting pressure on different parts of the exhaust. When I put pressure on the front end of the bolt-on straight pipe replacement of the cats, the rattle stopped. While not loose, it seems there is a sleeving issue creating the annoying rattle.

Now I could simply re-torque the bolts, but am wondering if experts in this area have any simple recommendations outside or welding the pipe on. Maybe it is how the clamp is placed, or maybe I should apply some heat wrap?

This seems like a simple fix, but would love your expert recommendations as windows-down driving would be so much better!

Petza914

You have a photo of the area you're talking about? Do you have exhaust gaskets in between the mated sections if it's at a joint?

jwbeck17

A picture is worth a thousand words...

I just took a picture of each side for reference.

Gary Knox

Hmm, looks like an absence of both steel and even iron oxide on the end of that first pix. Might rattle there??? Ha.

Petza914

It looks like either part of the pipes have rusted through, which means they might be vibrating against themselves, but more likely is that I looks like that pipe is in direct contact with the heat shield above it. If so, for sure that's the cause of the noise as the exhaust pipe vibrates against the heat shield. You'll need to create clearance between those.

bureau13

I've been battling (or, more accurately, living with) a similar problem for quite a while now. The thing is, while the description matches my symptoms almost exactly, I have felt that it wasn't an external rattling. It feels more internal, although I could definitely be wrong. For sure, I too hear it via open windows, so maybe it really is external.

The thrust bearing comments above are worrisome, but I have restart issues, the car is a 5-speed, and I checked and replace front and rear pinch bolts when I did my clutch a couple years back. Everything tends to blur with time but I THINK it was doing this before then. In the meantime, I think I should look into those...but my car is an '86.5 with headers, so I guess if they're on the exhaust manifold I won't have them...

jwbeck17

when I checked after installed the engine and trans mounts, I checked and confirmed that i still had some good space between the head shield and the exhaust including the clamps.

What is interesting is that I really didn’t think about the rust until I took the pics and it really popped out to me too. That was replaced back in 2013 and may be worth replacing now…especially if I can get a valved one like @PorKen has made!

jwbeck17

UPDATE: I FOUND THE NOISE!

I found that it was the actual X-pipe that was causing the rattle. It was a weld seam that was on the manifold side of the X, so right forward of the straight pipe. I would have never visually seen it or figured it out without applying this process:

With a cold engine and the car lifted, connect a shop-vac to the rear exhaust using the blower end of the vac. Tape it so there are no leaks where the hose goes into the exhaust. Mix up a spray bottle of water with some dishwashing liquid. Turn on the shop-vac and get under the car, spraying the soap water on every joint and connection, even if it is a welded connection. If is starts to create big bubbles, you know you have a leak.

I identified 5 air leaks, with two being problematic.One was around the O2 sensor (small) and one was the X-pipe intersection. There was also least and the fore and aft end of the straight pipe replacement and at a muffler interconnect.

I used a little muffler seal past to fill any tiny gaps and that seemed to do the trick. I also added a band clamp around the x-pipe leak area just to keep it tight.

I was inspired to do that on the Porsche as I just did it on my BMW that was claiming cat failure and it was actually due to an air leak around the back O2 sensor. OBD2 measurements verified that when the leak was sealed, the cat was working as desired.

Randy V

I haven't read all the replies, so you may have already found the culprit. If not, the noise you describe sounds much like a torque tube bearing going out.

edit - I see I was late to the party. Congrats on finding and fixing it. Sometimes these little things bring the most satisfaction.

jwbeck17

This was the noisemaker!

Thank's to Roger of 928srus I got a replacement x-pipe without cats and installed it this past weekend. The rattle noise is gone and the card is quieter from the drivers seat, though the V-8 bass is still there. Sounds much smoother through the acceleration and well tuned. Also less exhaust smell!

When I got the old unit down I saw the issue. There were no leaks on the underside of the pipes., but when I looked at the top I saw that a weld seam had split in the x--pipe area, going across the entire top of the pipe. This created more cabin noise (and probably heat) as well as exhaust fumes. Probably could be easily rewelded, but I choose a new x-pipe.

Mrmerlin

Note a real X pipe From Motorsport in Utah SLC was designed with Loui Ott’s input and many versions were made before the final product was released
A few vendors sell this fine product including Roger, installing one will result in about a 25 hp increase from a stock catted S4.

Im glad you found your noise,
your car should run great.

rjtw

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