Date: Sun, 9 Feb 2014 15:36:12 -0500
Reply-To: Jim Akiba <syncrolist@BOSTIG.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Jim Akiba <syncrolist@BOSTIG.COM>
Subject: Re: Exhaust Bushing Inner Weave Premature Failure
In-Reply-To: <CAB2Rwfi6gA2Zn2DG3_bx79TY=MueRECpbhxBV4ZD5Reozd5-rg@mail.gmail.com>
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Hey Neil,
What material are the primaries? Also the way they are welded is
sub-optimal which isn't helping. For tubes in flanges, it's best to
fully weld the face/tube opposite the side of entry into the flange,
then place 3 or 4 longish tacks on the entry side. This helps
strengthen the joint while offering more support to the tube by using
the thickness of the flange itself and not overheating the primaries
where they are weakest. In addition, if you have preloaded the
primaries at all they are going to crack... in addition, depending on
what material/thickness it is they may also stress corrosion crack in
the HAZ of the weld. With hotter temps cracking can be minimized with
thicker materials and better fillers as well as less heat. If you had
the tubes welded as I describe above, you'd have a smaller HAZ where
you see those cracks because the flange will protect the tube and sink
much of the heat from the welding.
Jim Akiba
On Sun, Feb 9, 2014 at 2:33 PM, Neil N <musomuso@gmail.com> wrote:
> And to further explain so others don't think I'm totally nuts ..... ha ha
>
> One of the big hurdles for me as a total newb to engine conversions
> was getting any kind of exhaust up and running even just for short
> test runs; I knew enough then to know that the joint between downpipe
> and flange at manifold needed to be 100% good. With a "factory" made
> downpipe, one might stand a better chance of at least cobbling
> together an exhaust to allow a trip to the local exhaust shop.
>
> The first welds to fail were at the joint from exhaust downpipe flange
> to downpipe. Ironically, these were done by a pro fabrication shop.
> BUT.... these happened after these cracks showed started. Image of V
> 1.0 cracks near pro welds: http://tinyurl.com/la6kgzh It was
> obvious that the issue wasn't the weld quality but my design and work.
>
> On 2/9/14, Neil N <musomuso@gmail.com> wrote:
>
>> My goal, in part, was to help others; I wanted to use OEM downpipe
>> bushing.
> --
> Neil n
>
> Blog: tubaneil.blogspot.ca
>
> '88 Westy http://tinyurl.com/c8rlw6p
>
> '81 VanaJetta 2.0 "Jaco" http://tubaneil.googlepages.com/
>
> Vanagon VAG *Gas* inline-VR Engine Swap Group:
>
> http://tinyurl.com/d7gd5ej
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