brazed with copper based alloys. Having been involved in the welding
industry for quite some time, I wouldn't consider a brazed engine mount.
Engine mounts are subject to significant vibration, which will cause a bit
of flexing. The brazing alloy, being softer than the CrMo tubing, will
flex, causing work hardening. This work hardening will almost certainly
lead to failure. I'd imagine, however, that many of the newer high
performance bicycles are being TIG welded, which will make a fine engine
mount.
Filler rod selection is one of those areas where you'll get as many opinions
as respondants. Historically, a good mild steel rod and a torch have been
the weapons of choice to attack the CrMo tubing. The high heat input of the
torch causes a LOT of deformation of the tubing, but the weaker weld
produced by the mild steel (typically 45-60 ksi) rod had enough elongative
properties to absorb the cooling stresses imposed by the stronger tubing
(110 ksi) as it cooled. If you're gonna use an oxyacetylene torch, by all
means use a mild steel rod, called RG60. Since the TIG process has become
the more modern choice, other options are available.
In the '70's, a welding fillermetal was developed for MIG welding of the
4000 series steels. Originally called E70s-1B, this has evolved into
E80s-D2. The 80 designates minimum tensile strength and the D2 indicates
that this is a special chemistry fillermetal, in this case it's Mn/Mo. A
TIG fillermetal, by the way, is reffered to as a ER80s-D2. The additinoal R
designates it's suitability as a filler ROD, in addition to being suitable
as an ELECTRODE. Although the D2 material produces a much stronger weld
than the RG60, the resulting elongative properties are not nearly as
forgiving. The fact that the TIG process produces a lot smaller heat
affected zone, means less stress and thus we can get away with less
elongation in our weld. The D2, by the way, is NOT heat treatable. The
next choice kicks it up another notch (sorry about that..). We can now
supply drawn 4130 rod in sizes small enough to use a filler rod. Although
not an AWS classed filler rod, the 4130 matches the chemistry of the tubing
exactly. The resulting weld, when properly produced, is as strong as the
tubing. (O.K., I know that the weld is essentially a casting and the
tubing, being drawn has better properties, but the 4130 weld comes as close
as is possible, without re heat treatment) This last bit is the biggest
difference. The 4130 rod IS heat treatable. So, if you're inclined to have
your mount stress relieved and heat treated to bring the properties back up
to the 110ksi range, the welds will also respond to the heat treatment, as
does the tubing. I haven't known anyone to have a mount, or any airplane
weldment, heat treated, but the 4130 rod is still the choice for matching
mechanical/ chemical properties on the CrMo tubing.
There are some who'll tell you that you've got to use AMS class, vacuum arc
melted filler rod with certification papers from here to the moon, to weld
on an airplane. If you're welding on a plane that our Government is buying,
they're right. The resulting weld won't be any better, but your rear will
be covered by a bunch of papers. Remember, LOTS of planes are flying that
were welded with big honking acetylene torches and mild steel rods. Why
spend $40.00 per pound of rod to use in a process that's nowhere near
perfect?
Bottom line; TIG weld it if you can. Use 4130 filler. If you can't find
it, send me a note off of the list and I'll sell you a couple of pounds.
Otherwise, get some ER80s-D2 filler at your local welding supplier.
Sorry about the wordiness. Remember crowd, the opinions you get here are
guaranteed to be worth the price!
Bill Delcambre
----- Original Message -----
From: <klehman@albedo.net>
To: <murphy-rebel@dcsol.com>
Sent: Monday, May 12, 2003 8:50 AM
Subject: Re: My V8 installation questions
*-------------------------------------------------------------------------*Rick
This is just a headsup offlist but I think bicycles are often brazed
which can be just as strong as welding. However there is a bit of
controversy where for example Richard Finch in "Performance Welding"
says that 4130 steel should never be brazed with any copper or bronze
based brazing material as it will lead to cracks. I think silver or
nickel based braze might be OK although more expensive. Anyway unless
you can find out for sure you might want to lean towards conventional
gas or TIG welding with mild steel rod. Some guys use heat treatable
filler rod but that seems pointless unless you actually heat treat the
finished engine mount. I gas welded mine with mild rod and it's not real
pretty but it's strong.
Ken
Rickhm at home wrote:Food for thought.... Engine mount... The guys that build custom bicycle
frames weld tubing all the time, all day. There designs are intended to
take large impact loading. I am going to contact one here in the Denver
area, see if it makes sense. Just a thought.
Rick Muller
SR70
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