Date: Sun, 21 Oct 2012 06:48:27 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Purchase price is just the down payment
In-Reply-To: <5F84398A-F9E6-4DAF-AFD8-B47FD8CA9F88@GMAIL.COM>
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At 12:57 AM 10/21/2012, turbowesty wrote:
>I'll explore that possibility. I was trying to find a way to get it
>as close to the turbo as possible so it would be the temp from all 4
>cylinders and that didn't look straight forward.
Silly me...forgot you had an inline engine, was thinking WBX in which
case you've got a couple feet of pipe to pick from.
>Is there a "usual" place to install?
This may be somewhat relevant:
http://www.thesamba.com/vw/forum/viewtopic.php?p=4035126
Ok, going on no experience here:
1) Should be upstream of the turbocharger, since that will introduce
load-dependent temperature drops as the turbo extracts energy from
the gas stream.
2) To get an aggregate temp, has to be somewhat downstream of the
manifold collection point. HOWEVER: Aircraft people may have one EGT
probe per cylinder. Very commendable, and makes lots of sense if
you're worried about falling out of the sky. Given that you're not
going to do that, I submit that an aggregate reading has
comparatively little advantage over a reading from any single
cylinder. If the cylinders are in balance it will make no
difference, and if they're not the aggregate reading will only
deviate by a quarter of the real difference. So even though it's
aesthetically inelegant, I'd be willing to monitor one cylinder and
stick the probe wherever it's easiest to get to and best protected,
as close to an exhaust port as convenient.
>And I've assumed stainless for the bung as it's easier to weld to
>cast, correct?
Welding to cast iron is technically demanding. The *correct* way to
involves heating the entire part to about 200C and the weld area to a
dull red before welding, and then cooling slowly afterwards buried in
ashes or other insulator. Especially for a used casting it's also
desirable to remove volatiles contamination by heating the weld area
to 475C for fifteen minutes and then wire-brushing. Preheating may
be minimized and possibly avoided by using a high-nickel filler metal
which is soft and allows deformation while cooling; and peening the
weld while hot. Brazing-welding is a more forgiving way of
attaching something to cast iron because of lower peak temps. See
http://www.esabna.com/EUWeb/oxy_handbook/589oxy15_5.htm et. seq.,
http://www.brazing.com/techguide/procedures/cast_iron.asp
That said, I've watched a machinist join two pieces of cold cast iron
by using stainless-steel electrode wire and tri-mix gas with a MIG
welder, making what were essentially glorified tack welds in several
places of the vee-grooved junction and continuing using the same
short welds in rotation to fill in between them and eventually
overweld the entire joint. I cannot remember whether he peened each
new weld segment. The part (drill press column about 4-5" diameter,
~3/8" wall thickness, broken clean across) worked in service and did
not come apart preferentially when the machine was later broken up
with a sledge hammer. The man was technically highly skilled but
with a habit of taking shortcuts in both his work and his life...
Anyway - I defer to people who've done it; but my own approach would
be to put the probe in a section of pipe instead or if placing the
sender on the manifold simply tap it for the proper NPT thread and
use no bung.
Only If neither of those is possible would I want to braze or
braze-weld it using "bronze" or perhaps nickel silver filler. I
wouldn't use silver braze metal unless I could arrange a
close-fitting (gap of a few thou) joint because it's very fluid when
heated and does not build up a bead (while in a properly fitted joint
it will readily flow in by capillary attraction). Bronze rod (really
brass) is particularly easy to build up by working torch and filler rod.
Yours,
David