Epoxy Bonding to Aluminum and Magnesium

[Ryan Young]

I'm working on a Hummel Aviation Ultracruiser Plus. The way the
engine mounts is quite different from the mounts on most VW powered
homebuilts. The Conventional Wisdom bolts the thing to the firewall
using the clucth end bellhousing, often with an accessory case in
between.

The Ultracruiser Plus is different. Two aluminum angles are bolted to
the sides of the magnesium case, in the sump area, and, suitablely
reinforced, are used to bolt Berry mounts to "bed" type engine
bearers built up out of aluminum, that extend from the forward
fuselage.

These angles are bolted and epoxied to the side of the magnesium case.
My point: what good is the epoxy?

It's probably not carrying any loads. A basic tenet of structural
design is that the stiffest load path carries the load, and the bolts
through the angle and into the case (secured with nuts and washers
inside the sump, before the engine is assembled) seem a bunch stiffer
that the epoxy.

It's not a sure stop against leaks. Epoxy is a wonderful material, but
it doesn't bond particularly well or reliably to metals. Plus, it's
mechanical properties, from it's modulus of expansion, to it's
ductility, are far different that the aluminum, steel, and magnesium
sandwich is it the Mayonnaise of. My concern is the epoxy will
eventually crack.

I lost the reply from Scott Casler of Hummel Engines, I'll paraphrase:

"The epoxy is to keep the angles from working and hogging out the
holes. The epoxy I use is a real good sealer, you've got to grind it
off."

My thoughts are this: LAP the angles to the side of the case (instead
of sanding with 80 grit), but use Permatex or Curil T to seal things.
Use close tolerance bolts in reamed holes in the side of the case and
the appropriate Loctite product to seal the bolts. And I'm inclined
to put the bolt heads INSIDE the engine.

Comments?

To see what this installation looks like:
http://flyhummel.com/forums/album_pic.php?pic_id=170

Ultracruiser (with 1/2 VW) is the same deal

[smjmitchell]

To be honest this all sounds like a bit of a mess.

There are a number of issues here ... however it is difficult to comment in
any detail until I know what sort of epoxy is specified and without further
details of the surface preparation and details of the design.

1. Most common epoxies have a Glass Transaition Temperature (Tg) of approx
90 deg C. If the epoxy is taken above that temperature then two things
happen ... first it softens and the stiffness and strength reduce
dramatically. Second irreveraible damage is done to the epoxy and it will
never be the same again - even when cooled. Unless you are using one of a
small number of epoxies that are designed for high temperature operation
(some of these have Tg of approx 400 F, 200 C I think without reaching for a
calculator) then it is certain I think that if used on an engine the 90 deg
C limit will be exceeded.

2. Next there is the issue of surface preparation. If the plans say prepare
by running with 80 grid paper then it is fairly clear that the guy who wrote
the plans knows little about what he is doing ! Epoxy metal bonding is
reliable if the surfaces are prepared properly but from what you have said I
doubt that is the case.

3. Bolted and bonded joints should be avoided because it is difficult to
predict the load transfer etc ... I won't go into detail on this - perhaps
later.

4. What are the differences in the thermal expansion coefficients of the
aluminium and epoxy ... from MIL-HDBK-5J alumnium is approx 12.5e-6 in/in/F
and Magnesium is 14.0e-6 ... not a lot of difference perhaps this is not an
issue.

5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
the galvanic table. That is a big different. You definitely need something
to separate the two or the magnesium is going to get gobbled up !!

6. I think galling of the metal is a possibility but if appropriate
tolerances are used for the bolts and holes than this would be less of a
problem. Hard to say without seeing the drawings etc. Sounds to me like if
the holes are flogging out then the design has some fundamental problems and
that one should not be relying on epoxy that probably cannot withstand the
temperatures to fix it.

My gut feel is that you need something between the alumnium and the
magnesium for corrosion protection and possibly the help the galling issue.
I would assume that this is sufficiently ductile an rubbery that it will not
pick up any load and that the fasteners will transfer all the load. I would
use a rudder like sealant compound that can take the temperature ... not
epoxy. When you use sealant of this type in a joint with fasteners extra
largers of safety should be allowed because of the extra flexibility that
this produces in the joint (typically an extra factor of 1.5).



"Ryan Young" > wrote in message
om...
> I'm working on a Hummel Aviation Ultracruiser Plus. The way the
> engine mounts is quite different from the mounts on most VW powered
> homebuilts. The Conventional Wisdom bolts the thing to the firewall
> using the clucth end bellhousing, often with an accessory case in
> between.
>
> The Ultracruiser Plus is different. Two aluminum angles are bolted to
> the sides of the magnesium case, in the sump area, and, suitablely
> reinforced, are used to bolt Berry mounts to "bed" type engine
> bearers built up out of aluminum, that extend from the forward
> fuselage.
>
> These angles are bolted and epoxied to the side of the magnesium case.
> My point: what good is the epoxy?
>
> It's probably not carrying any loads. A basic tenet of structural
> design is that the stiffest load path carries the load, and the bolts
> through the angle and into the case (secured with nuts and washers
> inside the sump, before the engine is assembled) seem a bunch stiffer
> that the epoxy.
>
> It's not a sure stop against leaks. Epoxy is a wonderful material, but
> it doesn't bond particularly well or reliably to metals. Plus, it's
> mechanical properties, from it's modulus of expansion, to it's
> ductility, are far different that the aluminum, steel, and magnesium
> sandwich is it the Mayonnaise of. My concern is the epoxy will
> eventually crack.
>
> I lost the reply from Scott Casler of Hummel Engines, I'll paraphrase:
>
> "The epoxy is to keep the angles from working and hogging out the
> holes. The epoxy I use is a real good sealer, you've got to grind it
> off."
>
> My thoughts are this: LAP the angles to the side of the case (instead
> of sanding with 80 grit), but use Permatex or Curil T to seal things.
> Use close tolerance bolts in reamed holes in the side of the case and
> the appropriate Loctite product to seal the bolts. And I'm inclined
> to put the bolt heads INSIDE the engine.
>
> Comments?
>
> To see what this installation looks like:
> http://flyhummel.com/forums/album_pic.php?pic_id=170
>
> Ultracruiser (with 1/2 VW) is the same deal

[Clay]

(Ryan Young) wrote in message >...
> I'm working on a Hummel Aviation Ultracruiser Plus. The way the
> engine mounts is quite different from the mounts on most VW powered
> homebuilts. The Conventional Wisdom bolts the thing to the firewall
> using the clucth end bellhousing, often with an accessory case in
> between.
>
> The Ultracruiser Plus is different. Two aluminum angles are bolted to
> the sides of the magnesium case, in the sump area, and, suitablely
> reinforced, are used to bolt Berry mounts to "bed" type engine
> bearers built up out of aluminum, that extend from the forward
> fuselage.
>
> These angles are bolted and epoxied to the side of the magnesium case.
> My point: what good is the epoxy?
>
> It's probably not carrying any loads. A basic tenet of structural
> design is that the stiffest load path carries the load, and the bolts
> through the angle and into the case (secured with nuts and washers
> inside the sump, before the engine is assembled) seem a bunch stiffer
> that the epoxy.
>
> It's not a sure stop against leaks. Epoxy is a wonderful material, but
> it doesn't bond particularly well or reliably to metals. Plus, it's
> mechanical properties, from it's modulus of expansion, to it's
> ductility, are far different that the aluminum, steel, and magnesium
> sandwich is it the Mayonnaise of. My concern is the epoxy will
> eventually crack.
>
> I lost the reply from Scott Casler of Hummel Engines, I'll paraphrase:
>
> "The epoxy is to keep the angles from working and hogging out the
> holes. The epoxy I use is a real good sealer, you've got to grind it
> off."
>
> My thoughts are this: LAP the angles to the side of the case (instead
> of sanding with 80 grit), but use Permatex or Curil T to seal things.
> Use close tolerance bolts in reamed holes in the side of the case and
> the appropriate Loctite product to seal the bolts. And I'm inclined
> to put the bolt heads INSIDE the engine.
>
> Comments?
>
> To see what this installation looks like:

I use a lot of Belzona products for a variety of industrial repairs
and find them to be very strong and reliable. www.belzona.com
You may want to use Black Beauty, Flint, Apache Blast, Alumimum Oxide
or some other angular abrasive. Sand, shot, beads, or sperical
abrasives do a good job of polishing but do not give a good profile
for an epoxy to bond properly.
A word of CAUTION, practice on a piece of scrap material before grit
blasting your project. Alumimum is soft and you could cause great
damage if you use too much pressure or dwell in the same place too
long.

http://flyhummel.com/forums/album_pic.php?pic_id=170
>
> Ultracruiser (with 1/2 VW) is the same deal

[Greg Reid]

"smjmitchell" > wrote in message >...
>
> 5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
> the galvanic table. That is a big different. You definitely need something
> to separate the two or the magnesium is going to get gobbled up !!
>

Interesting. Where might I information like this for making decisions
on what metals can be safely bolted together w/r/t galvanic corrosion?
At issue right now is whether it'll be OK to thread my brass
fuel-system finger strainers and fuel drains into aluminum blocks, but
other such questions will certainly come up in future.

Thanks,
Greg

[Ryan Young]

Thanx for yourlearned and informed reply.

"smjmitchell" > wrote in message >...

> To be honest this all sounds like a bit of a mess.

It does to me too, but on the other hand, there are a fair number of
flying installations like this, in spite of my "desk engineer"
concerns.

> 1. Most common epoxies have a Glass Transaition Temperature (Tg) of approx
> 90 deg C. If the epoxy is taken above that temperature then two things
> happen ... first it softens and the stiffness and strength reduce
> dramatically. Second irreveraible damage is done to the epoxy and it will
> never be the same again - even when cooled. Unless you are using one of a
> small number of epoxies that are designed for high temperature operation
> (some of these have Tg of approx 400 F, 200 C I think without reaching for a
> calculator) then it is certain I think that if used on an engine the 90 deg
> C limit will be exceeded.

That's about 190 deg F, which is a pretty comfortable oil temerature,
and this arrangement attaches to the side of the oil sump. But oil
temps up to 250 deg F need to be thought about. And that's higher
than most epoxy resins and adhesives, even post-cured.

I don't know what epoxy is used, I'll find out.

> 2. Next there is the issue of surface preparation. If the plans say prepare
> by running with 80 grid paper then it is fairly clear that the guy who wrote
> the plans knows little about what he is doing ! Epoxy metal bonding is
> reliable if the surfaces are prepared properly but from what you have said I
> doubt that is the case.

That's actually not outside the "standard of Care" for metal bonding
in low-stress operations. Gougeon brothers, makers of WEST and PRO-SET
epoxy, suggest sanding and etching for aluminum. The side of the
magnesium case is fairly rough, and not particularly flat. Sanding it
flattens it, removes the oxide coating, and still leaves some "tooth".

> 3. Bolted and bonded joints should be avoided because it is difficult to
> predict the load transfer etc ... I won't go into detail on this - perhaps
> later.

My point exactly.

> 4. What are the differences in the thermal expansion coefficients of the
> aluminium and epoxy ... from MIL-HDBK-5J alumnium is approx 12.5e-6 in/in/F
> and Magnesium is 14.0e-6 ... not a lot of difference perhaps this is not an
> issue.

There is also the steel bolts to consider, but their lower coefficient
of expansion actually tightens up the joint. Perhaps to the point of
fracturing the epoxy! I can't find good numbers on cured resin alone,
but cured composites have pretty low coefficients, like 2.0e-6.

>
> 5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
> the galvanic table. That is a big different. You definitely need something
> to separate the two or the magnesium is going to get gobbled up !!

Hmm, perhaps. I get that aluminum alloy is about -1.05. But look at
the difference between Cast Iron (-.5) and aluminum (-1.05). Lots of
cars, with WATER running through their engines, have cast iron blocks
and aluminum heads. In this situation, there is no ready source of
electrolyte. I don't see this as a huge concern. I'm more bothered
by oil leaks.

> 6. I think galling of the metal is a possibility but if appropriate
> tolerances are used for the bolts and holes than this would be less of a
> problem. Hard to say without seeing the drawings etc. Sounds to me like if
> the holes are flogging out then the design has some fundamental problems and
> that one should not be relying on epoxy that probably cannot withstand the
> temperatures to fix it.

Amen! Albeit, there are those pesky flying examples to be explained
away....
>
> My gut feel is that you need something between the alumnium and the
> magnesium for corrosion protection and possibly the help the galling issue.
> I would assume that this is sufficiently ductile an rubbery that it will not
> pick up any load and that the fasteners will transfer all the load. I would
> use a rudder like sealant compound that can take the temperature ... not
> epoxy. When you use sealant of this type in a joint with fasteners extra
> largers of safety should be allowed because of the extra flexibility that
> this produces in the joint (typically an extra factor of 1.5).

This aligns with my thinking. High Temperature Room Temperature
Vulcanizing Silicone rubber looks good for this. The security of the
joint would be in the close fit of the mating parts, not in the epoxy.
The bolts would be a tight fit in reamed holes, backed up with
Loctite Red.

> "Ryan Young" > wrote in message
> om...
> > I'm working on a Hummel Aviation Ultracruiser Plus. The way the
> > engine mounts is quite different from the mounts on most VW powered
> > homebuilts. The Conventional Wisdom bolts the thing to the firewall
> > using the clucth end bellhousing, often with an accessory case in
> > between.
> >
> > The Ultracruiser Plus is different. Two aluminum angles are bolted to
> > the sides of the magnesium case, in the sump area, and, suitablely
> > reinforced, are used to bolt Berry mounts to "bed" type engine
> > bearers built up out of aluminum, that extend from the forward
> > fuselage.
> >
> > These angles are bolted and epoxied to the side of the magnesium case.
> > My point: what good is the epoxy?
> >
> > It's probably not carrying any loads. A basic tenet of structural
> > design is that the stiffest load path carries the load, and the bolts
> > through the angle and into the case (secured with nuts and washers
> > inside the sump, before the engine is assembled) seem a bunch stiffer
> > that the epoxy.
> >
> > It's not a sure stop against leaks. Epoxy is a wonderful material, but
> > it doesn't bond particularly well or reliably to metals. Plus, it's
> > mechanical properties, from it's modulus of expansion, to it's
> > ductility, are far different that the aluminum, steel, and magnesium
> > sandwich is it the Mayonnaise of. My concern is the epoxy will
> > eventually crack.
> >
> > I lost the reply from Scott Casler of Hummel Engines, I'll paraphrase:
> >
> > "The epoxy is to keep the angles from working and hogging out the
> > holes. The epoxy I use is a real good sealer, you've got to grind it
> > off."
> >
> > My thoughts are this: LAP the angles to the side of the case (instead
> > of sanding with 80 grit), but use Permatex or Curil T to seal things.
> > Use close tolerance bolts in reamed holes in the side of the case and
> > the appropriate Loctite product to seal the bolts. And I'm inclined
> > to put the bolt heads INSIDE the engine.
> >
> > Comments?
> >
> > To see what this installation looks like:
> > http://flyhummel.com/forums/album_pic.php?pic_id=170
> >
> > Ultracruiser (with 1/2 VW) is the same deal

[Blueskies]

I was thinking ProSeal or similar for the interface...

"smjmitchell" > wrote in message u...
> To be honest this all sounds like a bit of a mess.
>
> There are a number of issues here ... however it is difficult to comment in
> any detail until I know what sort of epoxy is specified and without further
> details of the surface preparation and details of the design.
>
> 1. Most common epoxies have a Glass Transaition Temperature (Tg) of approx
> 90 deg C. If the epoxy is taken above that temperature then two things
> happen ... first it softens and the stiffness and strength reduce
> dramatically. Second irreveraible damage is done to the epoxy and it will
> never be the same again - even when cooled. Unless you are using one of a
> small number of epoxies that are designed for high temperature operation
> (some of these have Tg of approx 400 F, 200 C I think without reaching for a
> calculator) then it is certain I think that if used on an engine the 90 deg
> C limit will be exceeded.
>
> 2. Next there is the issue of surface preparation. If the plans say prepare
> by running with 80 grid paper then it is fairly clear that the guy who wrote
> the plans knows little about what he is doing ! Epoxy metal bonding is
> reliable if the surfaces are prepared properly but from what you have said I
> doubt that is the case.
>
> 3. Bolted and bonded joints should be avoided because it is difficult to
> predict the load transfer etc ... I won't go into detail on this - perhaps
> later.
>
> 4. What are the differences in the thermal expansion coefficients of the
> aluminium and epoxy ... from MIL-HDBK-5J alumnium is approx 12.5e-6 in/in/F
> and Magnesium is 14.0e-6 ... not a lot of difference perhaps this is not an
> issue.
>
> 5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
> the galvanic table. That is a big different. You definitely need something
> to separate the two or the magnesium is going to get gobbled up !!
>
> 6. I think galling of the metal is a possibility but if appropriate
> tolerances are used for the bolts and holes than this would be less of a
> problem. Hard to say without seeing the drawings etc. Sounds to me like if
> the holes are flogging out then the design has some fundamental problems and
> that one should not be relying on epoxy that probably cannot withstand the
> temperatures to fix it.
>
> My gut feel is that you need something between the alumnium and the
> magnesium for corrosion protection and possibly the help the galling issue.
> I would assume that this is sufficiently ductile an rubbery that it will not
> pick up any load and that the fasteners will transfer all the load. I would
> use a rudder like sealant compound that can take the temperature ... not
> epoxy. When you use sealant of this type in a joint with fasteners extra
> largers of safety should be allowed because of the extra flexibility that
> this produces in the joint (typically an extra factor of 1.5).
>
>
>
> "Ryan Young" > wrote in message
> om...
>> I'm working on a Hummel Aviation Ultracruiser Plus. The way the
>> engine mounts is quite different from the mounts on most VW powered
>> homebuilts. The Conventional Wisdom bolts the thing to the firewall
>> using the clucth end bellhousing, often with an accessory case in
>> between.
>>
>> The Ultracruiser Plus is different. Two aluminum angles are bolted to
>> the sides of the magnesium case, in the sump area, and, suitablely
>> reinforced, are used to bolt Berry mounts to "bed" type engine
>> bearers built up out of aluminum, that extend from the forward
>> fuselage.
>>
>> These angles are bolted and epoxied to the side of the magnesium case.
>> My point: what good is the epoxy?
>>
>> It's probably not carrying any loads. A basic tenet of structural
>> design is that the stiffest load path carries the load, and the bolts
>> through the angle and into the case (secured with nuts and washers
>> inside the sump, before the engine is assembled) seem a bunch stiffer
>> that the epoxy.
>>
>> It's not a sure stop against leaks. Epoxy is a wonderful material, but
>> it doesn't bond particularly well or reliably to metals. Plus, it's
>> mechanical properties, from it's modulus of expansion, to it's
>> ductility, are far different that the aluminum, steel, and magnesium
>> sandwich is it the Mayonnaise of. My concern is the epoxy will
>> eventually crack.
>>
>> I lost the reply from Scott Casler of Hummel Engines, I'll paraphrase:
>>
>> "The epoxy is to keep the angles from working and hogging out the
>> holes. The epoxy I use is a real good sealer, you've got to grind it
>> off."
>>
>> My thoughts are this: LAP the angles to the side of the case (instead
>> of sanding with 80 grit), but use Permatex or Curil T to seal things.
>> Use close tolerance bolts in reamed holes in the side of the case and
>> the appropriate Loctite product to seal the bolts. And I'm inclined
>> to put the bolt heads INSIDE the engine.
>>
>> Comments?
>>
>> To see what this installation looks like:
>> http://flyhummel.com/forums/album_pic.php?pic_id=170
>>
>> Ultracruiser (with 1/2 VW) is the same deal
>
>

[Bill Hale]

Where can U get Belzona products in the US? Bill Hale

[Ryan Young]

(Ryan Young) wrote in message >...

> These angles are bolted and epoxied to the side of the magnesium case.
> My point: what good is the epoxy?

I had further conversation with Scott Casler.
================================================== ===
Hi

I use a epoxy that is similar to JB Weld.

Scott ( Hummel Engines)
----- Original Message -----
From: <ryoung@>
To: <humeng@>
Sent: Monday, September 13, 2004 3:24 PM
Subject: What Epoxy do you use?


> To bond the aluminum angles to the side of the magnesium case?
>
> Thanx for your previous reply to my inquiries.
>
> Ryan Young
> Ultracruiser Plus Builder

================================================== ==

From the JB Weld web site:

Properties (lbs/psi)
Tensile Strength: 3960
Adhesion: 1800
Flex Strength: 7320
Tensile Lap Shear: 1040
Shrinkage: 0.0%
Resistant to 500º F

I'm not sure what "Resistant" means in this context. JB Weld is a
steel-filled epoxy adhesive. Belzona is much the same stuff, and I'm
intimately familar with both of them. Devcon is another brand, and
they have both the widest variety and the best technical information:

http://www.devcon.com/techinfo/107.pdf Aluminum filled epoxy.
Temperature Resistance Wet: 120°F; Dry: 250°F
Adhesive Tensile Shear 2,600 psi
Compressive Strength 8,420 psi
Modulus of Elasticity 8.0 psi x 10(5) in.
Flexural Strength 6,760 psi
Coefficient of Thermal Expansion 29 [(in.)/(in). x °F)] x 10(-6)

Wowee Kazowee, look how much it expands! Twice as much as aluminum or
magnesium!

http://www.devcon.com/techinfo/101.pdf Steel filled epoxy putty, more
like JB Weld
Adhesive Tensile Shear 2800 psi
Compressive Strength 8260 psi
Modulus of Elasticity 8.5 x 10(5) psi
Flexural Strength 5600 psi
Coefficient of Thermal Expansion 48 [(in)/(in) x °F)] x 10(-6)
Even more expansive, and not much stronger.

Application instructions <which cut pretty close to Hummel's plans>:
1. Thoroughly clean the surface with Devcon® Cleaner Blend 300 to
remove all oil, grease, and dirt. <This is probably a detergent - RRY>
2. Grit blast surface area with 8-40 mesh grit, or grind with a coarse
wheel or abrasive disc pad, to create increased surface area for
better adhesion
3. Clean surface again with Cleaner Blend 300 to remove all traces of
oil, grease, dust, or other foreign substances from the grit blasting.
4. Repair surface as soon as possible to eliminate any changes or
surface contaminants.

[Ron Webb]

> 2. Next there is the issue of surface preparation. If the plans say
prepare
> by running with 80 grid paper then it is fairly clear that the guy who
wrote
> the plans knows little about what he is doing ! Epoxy metal bonding is
> reliable if the surfaces are prepared properly but from what you have said
I
> doubt that is the case.

I recently did some testing with West Systems and aluminum. I used 3 test
strips, side by side. 1" wide fiberglass tape, 3 inches of bonding surface
on 6061.

The first strip was applied with no surface impression at all.
The second strip was applied after sanding with 80 Grit
The third was sanded and etched with an etch (Duramix 4925)

The first strip came off with maybe a pound of force, pulling on the end of
the fiberglass tape.
The second strip (sanded) took maybe twice that - it still came right off
The third (etched) strip never did come off, I tore the fiberglass tape It
stood up to at least 30 pounds in shear!

Surface preparation makes a BIG difference!.

[Leon McAtee]

(Ryan Young) wrote in message >...

>
> It's probably not carrying any loads. A basic tenet of structural
> design is that the stiffest load path carries the load, and the bolts
> through the angle and into the case (secured with nuts and washers
> inside the sump, before the engine is assembled) seem a bunch stiffer
> that the epoxy.

Been there, done that. The epoxy is more of a feel good thing. File
the sides of the sump flat, spot face the inside surface and bolt the
thing together with the bolt heads inside (no washers). Use some blue
Locktight on the heads and torque to the normal specs for the
fastener used and it won't leak.......at least that's been my
experience. A bit of Ultra Grey silicone doesn't seem to
hurt, as long as you get things torqued before it sets. You want good
metal to metal contact so things don't move around.

As for the corrosion issue, I haven't had any problems and I've
adapted this method to my ground bound VW's for attaching home brew
block heaters to the side since the old style oil sump things are so
hard or impossible to find anymore. If the corrosion isn't a real
problem driving on salted roads it shouldn't be a problem on an
aircraft.


All the above based on my personal experience only
==========================
Leon McAtee
Still looking for Aeronca C-2/3 factory drawings

[jls]

"smjmitchell" > wrote in message [...]> 5.
Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
> the galvanic table. That is a big different. You definitely need something
> to separate the two or the magnesium is going to get gobbled up !!
>

Interesting comment but the rear case on many A-65 Continentals, and on most
C-85's, is magnesium bolted to an aluminum alloy crankcase. The bolts, of
course, are cad-plated steel and there's a fat gasket between the cases.
Whenever I rebuild one of these engines I always use magnedyne to passivate
the magnesium and alodine for the aluminum case. Magnesium doesn't need
any contact with another metal to corrode like crazy, but it sure does make
a nice lightweight accessory case, including good bearing pockets for the
oil pump and its shafts. So you magnedyne it and paint it, and of course
paint the crankcase too after passivating it, just like the Continental
overhaul manual advises.

Aileron hinges on the later Taylorcrafts are magnesium, and so are the
yokes, and so are the wheels. Beautiful castings but they must be treated
and preserved with great care.

[Clay]

(Bill Hale) wrote in message >...
> Where can U get Belzona products in the US? Bill Hale

Depends on your location. Contact the Belzona website for your local
distributor or consultant. Sometimes you can find it at a Caterpillar
dealer but some of them mark it up a bunch.

The following is from the Belzona website:
With Belzona Distributors operating in over 120 countries, you are
never far away from Belzona products and service. Please contact the
appropriate Belzona Headquarters based on your geographic location and
the lead will be forwarded to your local Belzona Distributor.


To fill out an inquiry form for Belzona in North America, Latin
America and Asia:- Click Here
Belzona Inc.
2000 N.W. 88th Court
Miami, Florida U.S.A. 33172

Toll-Free 1-800-238-3280
Telephone: +1 (305) 594-4994
Facsimile: +1 (305) 599-1140

[Bob Kuykendall]

Sure, it works in practice. But does it work in theory?

[Ryan Young]

"Blueskies" > wrote in message >...
> I was thinking ProSeal or similar for the interface...

I was too, until I looked at the temperature resistance of
polysulfides (ProSeal being that). It's pretty low, it releases
pretty completely at about 250 deg F, whereas the cheapest RTV starts
from there, and they have readily available compounds that go up to
700 deg F or higher.

I've always looked down my nose at RTV, and I've seen many jobs
bodgered up using it, but in this case, I'm beginning to believe it's
the right goop for the deal.

[Vernon Klukas]

> > 5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
> > the galvanic table. That is a big different. You definitely need something
> > to separate the two or the magnesium is going to get gobbled up !!
>
> Hmm, perhaps. I get that aluminum alloy is about -1.05. But look at
> the difference between Cast Iron (-.5) and aluminum (-1.05). Lots of
> cars, with WATER running through their engines, have cast iron blocks
> and aluminum heads. In this situation, there is no ready source of
> electrolyte. I don't see this as a huge concern. I'm more bothered
> by oil leaks.

Auto engines have head gaskets between the electro different metals,
plus if you don't run an inhibitor is a mutli-metal water cooled engine
you will corrode the aluminum away, period.

Yours
Vern

[smjmitchell]

You are right but there is one other very important issue here ... age is
also a big factor in bond line strength. If you test your three samples in
three years time you will see different results. Some of the effects of poor
surface preparation don't show up for years. In other words you can prepare
samples in different ways now and test them and get similar shear and peel
strengths. If you test those same samples in three years you could see that
one has lost a lot of its strength and the other has retained most if not
all.

A very complex issue and no something that can be encapsulated in a simple
posting. Best to follow established process specifications. Companies like
Locktite (who now sell Hysol adhesives) have data sheets on their web sites
that you can download. Just get them and follow them with a lot of care.


"Ron Webb" > wrote in message
...
>
> > 2. Next there is the issue of surface preparation. If the plans say
> prepare
> > by running with 80 grid paper then it is fairly clear that the guy who
> wrote
> > the plans knows little about what he is doing ! Epoxy metal bonding is
> > reliable if the surfaces are prepared properly but from what you have
said
> I
> > doubt that is the case.
>
> I recently did some testing with West Systems and aluminum. I used 3 test
> strips, side by side. 1" wide fiberglass tape, 3 inches of bonding
surface
> on 6061.
>
> The first strip was applied with no surface impression at all.
> The second strip was applied after sanding with 80 Grit
> The third was sanded and etched with an etch (Duramix 4925)
>
> The first strip came off with maybe a pound of force, pulling on the end
of
> the fiberglass tape.
> The second strip (sanded) took maybe twice that - it still came right off
> The third (etched) strip never did come off, I tore the fiberglass tape It
> stood up to at least 30 pounds in shear!
>
> Surface preparation makes a BIG difference!.
>
>

[smjmitchell]

See below for data as requested:

Also see MIL-STD-899 for further info (you can download that from the web)
at http://stinet.dtic.mil/str/index.html


Metal Potential
Magnesium and its alloys -1.60
Zinc die-casting alloy -1.10
Zinc plating on steel -1.10
Zinc plating on steel, chromate passivated -1.05
Galvanised iron -1.05
Tin/Zinc (80/20) plating in steel -1.05
Cadmium-Zinc solder -1.05
Wrought Al-clad Al Alloys -0.90
Cadmium plating on steel -0.80
Aluminium alloy castings -0.75
Wrought aluminium -0.75
Non-stainless steel & grey cast iron -0.70
Duralumin type un-clad alloys -0.60
Lead -0.55
Lead-silver solder -0.50
Tin-lead solder -0.50
Tinned Steel -0.50
Cr plating (0.0005") on steel -0.50
Stainless 12% Cr -0.45
Tin plating on steel -0.45
Cr plating (0.00003") on plating steel -0.45
Chromium (99%) -0.45
Stainless High Cr (18/2) -0.35
Copper and its alloys (Brass, bronze, etc) -0.25
Nickel-Copper alloys -0.25
Stainless, Austenitic (18/8) -0.20
Silver solder -0.20
Monel metal -0.15
Nickel plating on steel Titanium -0.15
Titanium -0.15
Silver and silver plating on copper 0
Rhodium plating on silver plated Copper +0.05
Carbon +0.10
Platinum +0.15
Gold +0.15

Condition Max. Potential Difference
Marine and outdoor environment 0.3 Volts
Indoor environment 0.5 Volts
Interior assemblies, hermetically sealed No restriction




"Greg Reid" > wrote in message
om...
> "smjmitchell" > wrote in message
>...
> >
> > 5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V
on
> > the galvanic table. That is a big different. You definitely need
something
> > to separate the two or the magnesium is going to get gobbled up !!
> >
>
> Interesting. Where might I information like this for making decisions
> on what metals can be safely bolted together w/r/t galvanic corrosion?
> At issue right now is whether it'll be OK to thread my brass
> fuel-system finger strainers and fuel drains into aluminum blocks, but
> other such questions will certainly come up in future.
>
> Thanks,
> Greg

[smjmitchell]

Yes I would definitely alodine aluminium before bonding. Magnesium is a very
active (anodic) metal.

Of course the environment in which dissimilar metals interfaces operate has
a big influence on the likelihood and severity of corrosion. If the metals
interface is dry and sealed then you can get away with a lot ... if exposed
to moisture and or a salty atmosphere then you are in much bigger trouble !



" jls" > wrote in message
. ..
>
> "smjmitchell" > wrote in message [...]> 5.
> Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
> > the galvanic table. That is a big different. You definitely need
something
> > to separate the two or the magnesium is going to get gobbled up !!
> >
>
> Interesting comment but the rear case on many A-65 Continentals, and on
most
> C-85's, is magnesium bolted to an aluminum alloy crankcase. The bolts,
of
> course, are cad-plated steel and there's a fat gasket between the cases.
> Whenever I rebuild one of these engines I always use magnedyne to
passivate
> the magnesium and alodine for the aluminum case. Magnesium doesn't need
> any contact with another metal to corrode like crazy, but it sure does
make
> a nice lightweight accessory case, including good bearing pockets for the
> oil pump and its shafts. So you magnedyne it and paint it, and of course
> paint the crankcase too after passivating it, just like the Continental
> overhaul manual advises.
>
> Aileron hinges on the later Taylorcrafts are magnesium, and so are the
> yokes, and so are the wheels. Beautiful castings but they must be
treated
> and preserved with great care.
>
>

[Clay]

Vernon Klukas > wrote in message >...
> > > 5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
> > > the galvanic table. That is a big different. You definitely need something
> > > to separate the two or the magnesium is going to get gobbled up !!
> >
> > Hmm, perhaps. I get that aluminum alloy is about -1.05. But look at
> > the difference between Cast Iron (-.5) and aluminum (-1.05). Lots of
> > cars, with WATER running through their engines, have cast iron blocks
> > and aluminum heads. In this situation, there is no ready source of
> > electrolyte. I don't see this as a huge concern. I'm more bothered
> > by oil leaks.
>
> Auto engines have head gaskets between the electro different metals,
> plus if you don't run an inhibitor is a mutli-metal water cooled engine
> you will corrode the aluminum away, period.
>
> Yours
> Vern

Vern is 100% correct. I have repaired several automotive engines where
this has been a problem. I used Belzona Super Metal (1111) to repair
the problem. Also have used it to fix a multitude of diesel engines.
These were do to electroylisis and cavitation. This is caused because
the owners did not change or maintain the proper chemical balance of
the antifreeze.
Toyota engines require the Toyota antifreeze. Dexcool is not approved
and according to a Toyota engineer, it will eventually damage the
engine. He also told me not to mix Dexcool with glycol antifreeze.
To make a long story short, follow the engine manufactures
recommendations.

[Ryan Young]

(Leon McAtee) wrote

> >
> > It's probably not carrying any loads. A basic tenet of structural
> > design is that the stiffest load path carries the load, and the bolts
> > through the angle and into the case (secured with nuts and washers
> > inside the sump, before the engine is assembled) seem a bunch stiffer
> > that the epoxy.
>
> Been there, done that.

Oooh, that's what I like! Experience...

> The epoxy is more of a feel good thing. File
> the sides of the sump flat, spot face the inside surface and bolt the
> thing together with the bolt heads inside (no washers). Use some blue
> Locktight on the heads and torque to the normal specs for the
> fastener used and it won't leak.......at least that's been my
> experience. A bit of Ultra Grey silicone doesn't seem to
> hurt, as long as you get things torqued before it sets. You want good
> metal to metal contact so things don't move around.

Why no washers? The little bit of radius at the root of the shank of
the bolt needs somewhere to go, yes? And may I assume you're putting
these bolts in a reamed hole?

That got me to thinking. Taper pins.

http://assist.daps.dla.mil/docimages/0000/43/28/54217.PD4

Threads on the outside. I'll have to run the reamer in from the sump
side, through the aluminum angle and control the depth pretty
carefully.

I need to measure the thickness of the case walls to get the grip
length right, but I'm thinking an AN-386-2-9A from AS&S should do the
job. http://www.aircraftspruce.com/nsearch.php?s=taper

Another way to make the metal carry the load would be with locator
pins in reamed holes (called Shuffle pins when they're used on the
split line) to take the shear loads. I think with the tools and
tooling I have, the taper pins will be easier.

> As for the corrosion issue, I haven't had any problems and I've
> adapted this method to my ground bound VW's for attaching home brew
> block heaters to the side since the old style oil sump things are so
> hard or impossible to find anymore. If the corrosion isn't a real
> problem driving on salted roads it shouldn't be a problem on an
> aircraft.
>
>
> All the above based on my personal experience only
> ==========================
> Leon McAtee
> Still looking for Aeronca C-2/3 factory drawings

[Cam]

>
> Why no washers? The little bit of radius at the root of the shank of
> the bolt needs somewhere to go, yes? And may I assume you're putting
> these bolts in a reamed hole?
>
You'll find the bolt will bury itself into the aluminum or magnesium and
that little radius will tend to
squeeze the metal onto the shaft. Try it on a sample and have a look, the
bolt will be hard to get back out of the hole also.
A radius on the nut can do the same.

Cheers Cam

Ps. maybe not "aeronautically correct," but it works.

[Ernest Christley]

Vernon Klukas wrote:
>>>5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
>>>the galvanic table. That is a big different. You definitely need something
>>>to separate the two or the magnesium is going to get gobbled up !!
>>
>>Hmm, perhaps. I get that aluminum alloy is about -1.05. But look at
>>the difference between Cast Iron (-.5) and aluminum (-1.05). Lots of
>>cars, with WATER running through their engines, have cast iron blocks
>>and aluminum heads. In this situation, there is no ready source of
>>electrolyte. I don't see this as a huge concern. I'm more bothered
>>by oil leaks.
>
>
> Auto engines have head gaskets between the electro different metals,
> plus if you don't run an inhibitor is a mutli-metal water cooled engine
> you will corrode the aluminum away, period.
>
> Yours
> Vern

Rotary engines don't. Some people are running straight H20. Never
heard of that particular problem...period.

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

[Ryan Young]

(Ryan Young) wrote in message >...
> I'm working on a Hummel Aviation Ultracruiser Plus. The way the
> engine mounts is quite different from the mounts on most VW powered
> homebuilts.

Snipped to save bandwidth

> To see what this installation looks like:

FOR A 1/2 VW -- I've figured out since then that the full meal deal
needs 4 bolts, longer angles, and a new bolt pattern

> http://flyhummel.com/forums/album_pic.php?pic_id=170

I've posted a page of drawings, photos, and my usual snide remarks:
http://users.lmi.net/~ryoung/Sonerai/UCPlusEngMnts.html

Thanks for all who have contributed to this discussion!

[smjmitchell]

I have never seen an epoxy that will work to 500 deg F ... the limit from
what I have seen is approx 450 deg F and even that is pushing it. However
whilst some epoxies are claimed to be able to have Tg's of 350-450 F it is
not quite that simple. I know because I am working with these adhesives on a
current project ... in fact I have just had a series of Tg tests run non 4
different epoxies and the results were surprising. The issue is that you can
only achieve the high Tg numbers quoted by a very careful and usually very
complex post cure heating cycle. A homebuilder would never achieve this.
With a simple post cure (i.e. ramp up, hold, ramp down) some of the resins
with more modest Tg values will perform a lot better ... actually the Tg
numbers you will get from these resins will surpass those for the the resins
which claim higher Tg values.


"Ryan Young" > wrote in message
om...
> (Ryan Young) wrote in message
>...
>
> > These angles are bolted and epoxied to the side of the magnesium case.
> > My point: what good is the epoxy?
>
> I had further conversation with Scott Casler.
> ================================================== ===
> Hi
>
> I use a epoxy that is similar to JB Weld.
>
> Scott ( Hummel Engines)
> ----- Original Message -----
> From: <ryoung@>
> To: <humeng@>
> Sent: Monday, September 13, 2004 3:24 PM
> Subject: What Epoxy do you use?
>
>
> > To bond the aluminum angles to the side of the magnesium case?
> >
> > Thanx for your previous reply to my inquiries.
> >
> > Ryan Young
> > Ultracruiser Plus Builder
>
> ================================================== ==
>
> From the JB Weld web site:
>
> Properties (lbs/psi)
> Tensile Strength: 3960
> Adhesion: 1800
> Flex Strength: 7320
> Tensile Lap Shear: 1040
> Shrinkage: 0.0%
> Resistant to 500º F
>
> I'm not sure what "Resistant" means in this context. JB Weld is a
> steel-filled epoxy adhesive. Belzona is much the same stuff, and I'm
> intimately familar with both of them. Devcon is another brand, and
> they have both the widest variety and the best technical information:
>
> http://www.devcon.com/techinfo/107.pdf Aluminum filled epoxy.
> Temperature Resistance Wet: 120°F; Dry: 250°F
> Adhesive Tensile Shear 2,600 psi
> Compressive Strength 8,420 psi
> Modulus of Elasticity 8.0 psi x 10(5) in.
> Flexural Strength 6,760 psi
> Coefficient of Thermal Expansion 29 [(in.)/(in). x °F)] x 10(-6)
>
> Wowee Kazowee, look how much it expands! Twice as much as aluminum or
> magnesium!
>
> http://www.devcon.com/techinfo/101.pdf Steel filled epoxy putty, more
> like JB Weld
> Adhesive Tensile Shear 2800 psi
> Compressive Strength 8260 psi
> Modulus of Elasticity 8.5 x 10(5) psi
> Flexural Strength 5600 psi
> Coefficient of Thermal Expansion 48 [(in)/(in) x °F)] x 10(-6)
> Even more expansive, and not much stronger.
>
> Application instructions <which cut pretty close to Hummel's plans>:
> 1. Thoroughly clean the surface with Devcon® Cleaner Blend 300 to
> remove all oil, grease, and dirt. <This is probably a detergent - RRY>
> 2. Grit blast surface area with 8-40 mesh grit, or grind with a coarse
> wheel or abrasive disc pad, to create increased surface area for
> better adhesion
> 3. Clean surface again with Cleaner Blend 300 to remove all traces of
> oil, grease, dust, or other foreign substances from the grit blasting.
> 4. Repair surface as soon as possible to eliminate any changes or
> surface contaminants.

[Ryan Young]

(Ryan Young) wrote > That got me to thinking. Taper
pins.
>
> http://assist.daps.dla.mil/docimages/0000/43/28/54217.PD4
>
> Threads on the outside. I'll have to run the reamer in from the sump
> side, through the aluminum angle and control the depth pretty
> carefully.

Another dabbler chimed in:

> Hi Ryan,
> I am not keen on using taper pins in this application. You will be relying on
> the magnesium to hold the pins and I think it is a little soft for that task.
> It seems like the sandwich idea with the through bolts will keep the mount from
> moving around better.

> CW

AS21 and AS41 have compressive yields up around 20ksi, comparable to
2024 - in the Annealed state! In the tempers we usually use for things
like wing spars, the yield is about 62K.

Plus, it looks like there is no way to get a reamer in from the case
side anyway. See the web page I built last night,
http://users.lmi.net/~ryoung/sonerai/UCPlusEngineMnt.jpg

Scratch that idea. Back to AN3 bolts in reamed holes, hold the epoxy
;-)

[Leon McAtee]

(Ryan Young) wrote in message >...
> (Ryan Young) wrote in message >...

>
> I've posted a page of drawings, photos, and my usual snide remarks:
> http://users.lmi.net/~ryoung/Sonerai/UCPlusEngMnts.html

Re the question on your site about removing the oil pick up:

Remove the 10mm bolt/nut, heat around the front with a propane torch
and wiggle. The tube should come out fairly easly. Older cases are
more work. Reverse the procedure to install. If your lucky all will
be well. A bit of "bearing n stud mount" helps seal. If your really
picky check to see that it holds a vacuum. Some stock tubes get
cracked so this may not be a bad idea anyway................

Some really old cases don't have the hold down 10mm nut. A 17mm nut
(old case nut)welded/brazed to the top of the tube (under the cam
bore) keeps the tube from rotating up and out of the oil.
==============
Leon McAtee
Still looking for Aeronca C-2/3 factory drawings

And maybe a Franklin 2A-120