83 case composition

[Wildebeest90210]

Dropped my engine cases of for resto today. The guy would like to know the magnesium content as it affects the way he will treat them. Also it affect the decision to leave them with a vapor blasted finsh or paint.
Apperently they will blacken and oxidise quickly if high content of magnesium.
Any ideas/experience ?

 

[fran...k.]

They are cast magnesium. Sure there are some other elements but when I was looking for magnesium welding rods it was basically cast or extruded. The magnesium/aluminum phase diagram is pretty complicated and not very much aluminum is soluble in magnesium at room temperature, probably less than 5 percent. Any idea of what alloying elements could be in magnesium to not make it grow white powder from sitting in air like some stuff I have has done. Of course it had to be my new unused case set that grew the white stuff (on some unpainted surfaces) but not too bad before I put premix oil on it. I think the welding rods grow white stuff faster.

 

[dukkman]

Sand blast then wash the dust off in tap water and watch what happens.

 

[Wildebeest90210]

He did mention something with wallnut shells.....

 

[Wildebeest90210]

They are cast magnesium. Sure there are some other elements but when I was looking for magnesium welding rods it was basically cast or extruded. The magnesium/aluminum phase diagram is pretty complicated and not very much aluminum is soluble in magnesium at room temperature, probably less than 5 percent. Any idea of what alloying elements could be in magnesium to not make it grow white powder from sitting in air like some stuff I have has done. Of course it had to be my new unused case set that grew the white stuff (on some unpainted surfaces) but not too bad before I put premix oil on it. I think the welding rods grow white stuff faster.

Just wikipedia'd mag alloy so a little wiser. I got this list
Cast alloys
Magnesium casting proof stress is typically 75-200 MPa, tensile strength 135-285 MPa and elongation 2-10%. Typical density is 1800 kg/m3 and Young's modulus is 42 GPa.[1] Most common cast alloys are:
AZ63
AZ81
AZ91
AM50
ZK51
ZK61
ZE41
ZC63
HK31
HZ32
QE22
QH21
WE54
WE43
Elektron 21
I wonder if anyone actually knows which one was used on the early 80's crankcases or has that been lost in the mists of time?

 

[Larsa]

Guys,
Now I don't know what the actual alloy is, but I would assume that a protective coat is neccessary for the parts, and acutally would propose using some sort of shielding between the magnesium and other alloys. These engines get watersprayed and dirty for obvious reasons, and to avoid degradation of the properties through galvanic corrosion over time (which is really the drawback for the otherwise great magnesum element - all other practical design alloys will be more noble in this sense I guess).

Just my thoughts on the issue,
Thanks
Lars

 

[fran...k.]

As to post #6 and galvanic corrosion. If you are in a classroom discussing this it is generally drawn in a circle, the circle being an electolite generally water with dissolved elements, the metal Me goes to M+(dissolved in the electrolite) and the electron goes into the piece of metal to anogher half reaction elsewhere within the circle of the electrolite on the blackboard. Maybe I even screwed it up but the generall idea if it is dry it won't happen.

As to the origional post and vapor cleaning which I am guessing is cleaned well beyond the kerosene stuff I do, The welding rods corroded sitting on the shelf, the unused but it must have had some sort of preservative cases corroded a little sitting in similar air, The used cases cleaned with paper towels in the same environment didn't corrode in that environment but some corrosion is visible in some crank cavities and some water pump areas. This is not strictly a Husky thing, there is a guy who enters some of same classes I do and had a ktm 1985 or so and had the cases changed under warranty due to corrosion. It might not necessaraly be the alloy now with the internet I find somewhere around 1965 there were emission rules put in place and the BMW heads for a couple of years after that are called butter heads, never had any of them but did have both single and double port vw heads with cracking problems.

I have over the years had manuals for a lot of things and by far Norton is the best as far as stating alloys of various parts. Let's see Husqvarna now has the 650 engine made in country x, the 450/510 engine made in country y, the ultra lite 250/310 four stroke, the 250/300 two stroke, the 125 and the big bore kit, the te 125 minarelli owned by yamaha engine, and the kid bike that I can list. If someone wants to find out all the alloys used and post them much appreciated.

I could add that with my dinosaur welder and pure argon I can weld the cases and the clutch cover but have failed on the rear backing plate for most of the mono shock bikes which hammers itself and also failed at the magnesium cover to the electric generator thing on my 1998 125.

 

[jimspac]

I have to remove the crank web from a centercase set from an 84 250CR W/C to use for my 430WR. What should I coat the bare magnesium with to protect the cut surfaces?

Also never use glass bead or silica carbide grit on mag or aluminum. Crushed walnut shells or soda blast is better for these materials

 

[GaryM]

I have to remove the crank web from a centercase set from an 84 250CR W/C to use for my 430WR. What should I coat the bare magnesium with to protect the cut surfaces?

Also never use glass bead or silica carbide grit on mag or aluminum. Crushed walnut shells or soda blast is better for these materials

I also have a set of older cases i started to work with the white corrosion I want to use in future. I have just cleaned them up two days ago thought they were all clean and ready but just a day later my white rust is back. That is the question after we remove the corrosion what material, compound, solvent do we use to stop further corrosion with. And again what is causing it to react so fast just the air, cleaner ,etc.

Funny thing is on the same shelf I have same year cases spilt and open to air with not a bit white rust as I call it showing anywhere. I am going to soda blast again to see the next reaction.

Is their a metal pre wash, fast etch, etc for mag cases we have to discover to stop this Flash white rust/ powder/ corrosion to happen ??

 

[Larsa]

When I fabricated alot of aluminium parts I used to put an etching primer on it + paint, but due to the very toxic nature of it I decided to stop using it. Al (alloyed AL) parts are sensetive to corrosion if not plated with pure AL on the surface (alclad) which then allows for an oxide barrier to build and avoid corrosion. Unfortunately Mg have less build up capability of a protective barrier I beleive. The correct procedure of using etching or non-etching primer on the husky alloy I do not know, but I will use an epoxy based primer on my 430 case which has, where the paint is worn away, signifficant corrosion on it unfortunately.

I experience the same thing on my beetle engine case which is Mg alloy as well.

Honestly, I can see very few advantages with Mg alloy castings for engines, the primary advantage in my head is its castability, weight and in some cases cost. It is a quite weak material in terms of modulus and I would argue it is questionable if you are able to alleviate its low density in this application.

 

[jimspac]

I also have a set of older cases i started to work with the white corrosion I want to use in future. I have just cleaned them up two days ago thought they were all clean and ready but just a day later my white rust is back. That is the question after we remove the corrosion what material, compound, solvent do we use to stop further corrosion with. And again what is causing it to react so fast just the air, cleaner ,etc.

Funny thing is on the same shelf I have same year cases spilt and open to air with not a bit white rust as I call it showing anywhere. I am going to soda blast again to see the next reaction.

Is their a metal pre wash, fast etch, etc for mag cases we have to discover to stop this Flash white rust/ powder/ corrosion to happen ??

There was a discussion about treating corrosion and a link to aircraft proceedures. It involved a grade of acid not recommended for use by mere mortals and I consider myself "'mere" enough for the Law of Murphy to apply. Basically clean as much as you can with stainless wire brushes, treat with an etching solution, DO NOT TOUCH ANYTHING in repair region with bare fingers as the touch will contaminate just like causing fisheyes in painting. You will need to coat with maybe an epoxy etching primer , allow to cure and watch to see if corrosion rises from under it. Not easy to do right!!

 

[Larsa]

Jimspac,
Thats excactly what I did, made a bunch of Aircraft parts using solution requireing breathing mask with overpressure. Not worth it...when the misses was expecting my second kid I god rid of everything, including the spray guns as the formula I used was very, very bad for babies in the belly. This is now some years ago and these days I ALWAYS choose less risk over stated better capability. Always.

 

[fran...k.]

Diverging a bit from the title of this thread.

Without looking up figures I was under the impression that magnesium was more rigid than aluminum. Of course we would have to discuss alloys here not much is as maleable as pure aluminum. Admittedly I have never had any pure magnsium to play with. The magnesium welding rods I have are definately more rigid than 4043 or 5356 aluminum.

I have a four stroke case half, one with the 12 mm hole for the swingarm which sure appears to be aluminum. It weighs more totally empty than a two stroke 400,430,500 case half with all the bearings still in. I also notice that the magnesium one has a magnetic insert at the crank bearing and the aluminum one doesn't. For those of you really wanting to do the restoration right you probably should sleeve that beaing pocket behind the clutch as it is generally in my stuff a drop in fit at best.

Fran

 

[Larsa]

I agree, probably my fault that took this thread to a general materials discussiont, I apologize, I can't help it when talking materials/structures engineering which I find very interesting. Hopefully somone share my interests, if not I shall not elaborate anymore.

Mg is much less 'stiff' then AL. Typically when designing or selecting Mg vs Al you want to evaluate the loading and possibly take advantage of Mg's lower density and if possible design with geometrical stiffness instead.
Alloying not very signifficant for youngs modulus and selection of heat treatmen won't affect it (contrary to yield and rupture strength)

If one would just take the ration of young's modulus / desity you will find that most common metallic materials (Steel,Mg, Alu, Ti) will have about the same performance. So basically one finds that to obtain a certain stiffness you will end up at similar weight if you would only consider tension/compression. However for bending, the story is different, due to the fact that the cross-section stiffness will be proportionally cubic to the height. This means that if a part is subjected to bending you can, using Mg, build a bigger cross-section at the same weight and take advantage of the fact that a bigger cross-section is signifficantly stiffer, and then end up with a both stiffer and lighter part, and better to cast with fewer defects.

 

[Wildebeest90210]

I am finding this discussion very interesting indeed. From knowing nothing I now have a head filled with all sorts of Mg information. I have spoken to my work welding/metallurgy group at work and they are looking in to sampling to come up with a breakdown of elements in the cases just out of interest.
I like to know how my engines are working while I ride, if I can visualise what they are actually made from I may ride even faster !!!

 

[1Tuff500XC]

I always thought mag parts made a bike faster.......Just like a clean bike is faster.....Remember that from way back.......lol, JK. A great placeboe effect though, one of the best..

 

[Wildebeest90210]

Vapour blasted very carefully. Masked up and small test patches first.
Not all the paint taken off, whatever it is it's very tough. Can't be shifted without risk of damage. I think maybe it was the factory finish, my thoughts being they painted the inside of the engine to protect the magnesium. I found paint flaking off which obviously can gum things/block oilways but maybe husky never thought their engines would still be getting a pasting 30 years on. Any paint that is still there wont be shifted by another 30 years if the vapour blasting won't shift it. Got the crank section squeaky clean though.
Bearings in and a coat of acrylic on the outside and oil on the inside pronto.

 

[dukkman]

I am wondering why they all seem to corrode at the below the flywheel.
You would think that the paint and two stroke oil would prevent this.
The 400 shown in my avitar was eaten right through even though the engine was complete and had been for years.
When I first kicked it over [ before it was rebuilt ] it blew the corrosion out and the old two stroke oil/fuel ran out
Condensation ?

 

[Wildebeest90210]

First time I've stripped one of these so hadn't really thought, condensation sounds plausible though over time ?

 

[1982 XC 430]

Maybe we could go back to the Paint subject. Like what etching Primer and what Paint has been used with sucess. I don't want this to happen again!