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Exhaust Sealing Donut(s) What Is Their Purpose?
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Vanagon Nut
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PostPosted: Sun May 06, 2012 11:39 am    Post subject: Exhaust Sealing Donut(s) What Is Their Purpose? Reply with quote

Hi all

There's speculation in this thread:

http://www.thesamba.com/vw/forum/viewtopic.php?t=437618&highlight=exhaust

that the metal donut installed on some systems here:

http://www.thesamba.com/vw/forum/album_page.php?pic_id=458764

is there to help ease assembly. (provides end user with more flexibility in adjusting position of parts?)

True? Or....

is it used purely to provide a flex joint to reduce engine vibrations over the long term (if that's even a risk) from causing the cat/muffler to crack?

And, in this pic:

http://www.thesamba.com/vw/forum/album_page.php?pic_id=458762

Why are the washers there? Bentley calls them "diaphram springs". They don't look like they have any "give" to me.

And looking at GW exhaust gasket kit,

http://www.gowesty.com/images/ec/products/large/large_69eb8d841a2e4e87c8657ceac49470ba.jpg

I see two metal donuts. I assume one is used at this joint.

http://www.thesamba.com/vw/forum/album_page.php?pic_id=458762

A point of curiosity and edu-ma-cation but also would save me time sourcing fibre donuts for these two joints.

Neil.
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D Clymer
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PostPosted: Sun May 06, 2012 10:03 pm    Post subject: Reply with quote

Hi Neil,

I think the metal donuts are there strictly to allow the angle of the J-pipe to be adjusted to align properly with the inlet of the cat. These joints don't really function as a flex-joint. When all three bolts are tight, the joint becomes pretty rigid.

D
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Vanagon Nut
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PostPosted: Sun May 06, 2012 10:32 pm    Post subject: Reply with quote

D Clymer wrote:
Hi Neil,

I think the metal donuts are there strictly to allow the angle of the J-pipe to be adjusted to align properly with the inlet of the cat. These joints don't really function as a flex-joint. When all three bolts are tight, the joint becomes pretty rigid.

D


Thanks much David.

Haven't got my exhaust back together yet but I can "see" what you mean.

I see things through the eyes of my swap, so even though the boxer is a much smoother design, I tend to think that way. (be paranoid of exhaust system cracks)

Helpful to know purpose of donut. With J pipe still mounted, it seemed the ID might have been flared (it was fouled with rust etc.) I cleaned the hole out with a file, then free handed with Dremel. Got it close but unless I lap the surface, or use a fibre donut, it won't seal. I have to stop shaping as I'll run out of metal for gasket to still work.



Neil.
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j_dirge
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PostPosted: Mon May 07, 2012 7:13 am    Post subject: Reply with quote

Vanagon Nut wrote:
With J pipe still mounted, it seemed the ID might have been flared (it was fouled with rust etc.) I cleaned the hole out with a file, then free handed with Dremel. Got it close but unless I lap the surface, or use a fibre donut, it won't seal. I have to stop shaping as I'll run out of metal for gasket to still work.

Yep.. allows for some angle variation between cast 2-to-1 uniton and the cat inlet.
I have a newer J- pipe.. and just installed a new cat and muffler.

I'd have like to have seen the orirginal set up as is shown in the Bentley.
The dwg is not real clear.

So...
Even with complete disassembley, in my case, it was not possible to get a straightish line thru the j-pipe.. It pumped exhaust out at the first joint.
In fact I think I could shorten the j-pipe about 1/4-3/8" (maybe more, then reflare it) and it would fit better and allow the cat/muffler assembly to roatate a bit downward. Maybe next tome.

Cleaning the inside of the flare will help with sealing.. but it also help to use heat when bolting down.

I bolted snug with everything at ambient temps... and muffler straps loose. Then snugged down the muiffler. and the rear header support.

I drove it a bit to allow it to work out vibration shifts. Just long enough tot reach operating temps.
Then I snugged down the bolts some more while still warm..
I hit the 2-1 union to j-pipe jointy with torch heat. Plenty of heat but not red hot.. and then torqued down on bolts more. I could feel the stretch.
Maybe a nother 3/4 turn on some bolts.. only a 1/4 on others.
I was cautious here, cuz I really don't know what I am doing sometimes.. and I did not want to break something or strip the bolts.

Then I did similar at the cat but not as hot. (with O2 sensor and wiring tucked safely out of the way)

Both joints still leak a drop or two of condensation upon start up.. but there is minimal exhaust leaking at these joints now.
I used to feel a pulsing of hot air.. now its negligible

Seems thats the best I could do, thus far.


I am sure the more learned have some other tips. This was what I was comfortable with limited experience and tools.. It seems to work much better than before. Wondering what, if any, improved mpgs I might see in HWY use. The system had some major leaks prior.
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Vanagon Nut
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PostPosted: Mon May 07, 2012 8:58 am    Post subject: Reply with quote

Thanks j_dirge.

On my '88, joint at inlet of J pipe looks a little cockeyed. And, no stacks of washers present. Likely J pipe and/or mani replaced at some point. My point: cat/muffler position likely skewed the J pipe inlet join. If parts replaced, maybe installer should have slacked off the muffler brackets at engine to allow alignment at J pipe joint? Speaking of the stack of washers......

@ j_dirge and list:

What exactly do these "5 Diaphragm Springs" do? (P. 26.9 Bentley). Do they provide a flex joint? Can't see how as I've never seen the OEM parts in hand.

Anyhow.....

Now I see why donuts are used (on some) and why holes on exhaust bracket to engine are ovaled.

If "room" allows, I will leave parts loose at engine to muffler, align cat inlet to J pipe, tighten muffler/cat to engine.

Neil.
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j_dirge
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PostPosted: Mon May 07, 2012 9:57 am    Post subject: Reply with quote

Vanagon Nut wrote:

@ j_dirge and list:

What exactly do these "5 Diaphragm Springs" do? (P. 26.9 Bentley). Do they provide a flex joint? Can't see how as I've never seen the OEM parts in hand.
Neil.

I do not know..
I have not seen them either.
When I bought my van, used, the exhaust had straight bolts and copper nuts in that location.

That said, my aft header has failed twice.. both failures appeared to be due to vibration and stress.
In one case, a crack mid-pipe near the hanger, (welded, then failed again).. The second, newer pipe, failed at the flange weld at the head (!?). Pipe looked fine, only 4 yrs old.. flange looked fine, but the weld parted between the two.

I can't help but think that some sort of flex joint would be of benefit in there.

Quote:
Anyhow.....

Now I see why donuts are used (on some) and why holes on exhaust bracket to engine are ovaled.

If "room" allows, I will leave parts loose at engine to muffler, align cat inlet to J pipe, tighten muffler/cat to engine.


The bolt holes at the muffler hanger are ovaled to allow some "adjustment".. but not enough in my case. If there is a next time, I will elongate them another 1/16"-1/8"
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89 GL Westy, hummng along again under the power of a used "WBXer of mystery"

danfromsyr wrote:
those are straight line runs with light weight race cars for only 1/4mile at a time..
not pushing a loaded brick up a mountain pass with a family of 4+ inside expecting to have an event free vacation..
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Vanagon Nut
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PostPosted: Mon May 07, 2012 10:27 am    Post subject: Reply with quote

J_dirge.

re: diaphragm springs. Found this info (Dennis is a very knowledgable reliable source)

http://gerry.vanagon.com/cgi-bin/wa.exe?A2=ind9808E&L=vanagon&P=R4862

Is the strut at d-side part of header present on your rig?

There's tried and true methods existing, but....

I too thought "flex joint" but at manifold & J-pipe union. But. I doubt this would benefit parts pre manifold. And, unless flex bushing welded straight to parts concerned, (even then it might push cat/muffler toward rear too much) a flanged flex bushing would obviously push the cat/muffler toward rear; no room for the part really IMO. I think one would either have to make new parts or hack up existing. The latter not something I'd do.

Neil.
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Vanagon VAG GAS engine swap Google Group:
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240Gordy
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PostPosted: Mon May 07, 2012 11:14 am    Post subject: Re: Exhaust Sealing Donut(s) What Is Their Purpose? Reply with quote

Vanagon Nut wrote:
Hi all
And, in this pic:

http://www.thesamba.com/vw/forum/album_page.php?pic_id=458762

Why are the washers there? Bentley calls them "diaphram springs". They don't look like they have any "give" to me.

Neil.


can't see the pic but if they are dish shaped washers, where I worked they were known as "cup" washers and they do give. Dopplmayer ski lifts use them in detachable carrier lifts. The grips I worked on had spring packs of 144 washers, a lever would compress them as the carrier enters the station, the grip would open and be separated from the haul rope. I had to test each washer for function . . .

Image may have been reduced in size. Click image to view fullscreen.
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j_dirge
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PostPosted: Mon May 07, 2012 11:24 am    Post subject: Reply with quote

Vanagon Nut wrote:

Is the strut at d-side part of header present on your rig?

yes.. its there.

The previous 4 yr old header that failed never fit properly. And it showed other manufacturing flaws.. I am thinking that the stress from "force" bolting to the union may have contributed to failure.. and/or it was a crappy weld. (I have heard other stories of the weld quality).

I purchased a replacement a few weeks ago that fits much better.
<knock on wood>

And yeah.. the flex joint I think that would be beneficial would be in there between 2-1 union and cat.. maybe hacking the j-pipe to do it.

That would allow for a flat face flanges at the union and at the cat, as well.
Could probably have something fabbed like that at the local shop for $100-$200.


Any fabricators out there think this is a worthwhile product?
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89 GL Westy, hummng along again under the power of a used "WBXer of mystery"

danfromsyr wrote:
those are straight line runs with light weight race cars for only 1/4mile at a time..
not pushing a loaded brick up a mountain pass with a family of 4+ inside expecting to have an event free vacation..
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