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turbohead

Magnesium Welding

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Having recently made a typical barn find, a ´81 TL320, the need for magnesium repair is very obvious. I have done it before and I have the equipment, but when looking at the transmission case I and other parts, I still hesitate. This is not the best castings I have seen and after a long life soaked in oil, it will take some hours of cleaning, blasting, degreasing, grinding and so on before I even order the rods and take my TIG welder out. For example, state of the damage on the transmission side include sveral cracks, holes and worn out threads to deal with, previously "fixed" with bad epoxy and thick paint several years ago, making the welding a process in several steps and probably machining all surfaces after the case has cooled down.

 

What have others done before me? Welding or better, modern epoxy?

 

Is there any hope of new or used parts somewhere or do I have too make another barn find to be able to build one good bike out of parts...?

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May be a better idea to contact the very helpful Martin Mathews at - www.motoswm.com  he may well have them ready to use.

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Cleanliness is the main thing,but a few years back when I was messing around alot with TY250's I tried out a Tig weld on a cut off piece of the magneto cover.A waste of time, I didnt have any rods,but the material just turned into cheesy ball like lumps, it was too old and oxidised to cope with being welded.

Around the same time I was asked to weld a crack in a GSXR750 crankcase cover - made of magnesium. It was just a hairline crack,but leaked oil badly.A good cleanup and plenty of back gassing and it welded beautifully,no rods it just healed back together.

So my advice is just to try melting it with the Tig,see how it behaves,if its good go for it.If not JB weld is very good,my rat TY250 has a very porus clutch cover sealed from the inside with JB,works a treat. 

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I had a Jumbo clutch case with a big hole in it welded from a specialist for magnesium welding.

It was well worth the small amount it costed.

Go on the Internet and look if there´s a company in the area

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Whether it can be decently welded depends on the exact alloy composition. I would keep it in near boiling water + janitol heavy duty degreaser at 10 or 20:1 for several hours at least. Then try welding one of the small cracks. Cut out using a carbide burr then weld using 4043 filler.

Big problem with high % magnesium castings is cracking on solidification and cooling due to very high coefficient of thermal expansion.

 

Yam TY 250 ignition cases are effectively un weldable whereas TYZ clutch cases weld quite readily, you just can't tell till you try.

 

I find JB weld to be the best of the epoxies but some get very good results with Devcon.

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Thanks all for your replies to this. However, considering how hard it is to find certain parts when needed, I decided to have a go with my new TIG inverter. And the results are surprising, to say the least. No problems whatsoever, just clean and clean again, carefully set up all parameters involved and then careful welding, of course. Rather good results considering condition of the old parts, with old welds and so on. An hour or so of grinding and finally some paint. Not as new, but that was not my intention, just making useful parts out of badly damaged ones.

 

I'll post some pics later and also some welding details if anybody is interested. Just remember: Magnesium is perfectly weldable with the right equipment and some practice!

 

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Here are a couple of photos, before and some stages later. The main problem is cleaning, in my case even more so as the parts had been (badly) welded in the past, as can be seen from all the pores. I could have taken all those away by grinding, but I was afraid of warpage and post welding cracks and decided to leave it and repair the worst holes, broken lugs and cracks instead. Before welding, I used an industrial ultrasonic parts cleaner and lots of acetone. Then grinding, almost like your dentist, to clean all surfaces to be welded, from cracks to pores. Took some time.

 

Before welding I pre-heat the parts for about 1 hr in an ordinary kitchen owen at 200 deg C. After welding I put the parts back for 1 hr in 250 deg C and then for 10-12 hrs in 200 deg C. Finally, slowly cooling off in room temperature.

 

The welding job itself is rather like TIG-welding anything aluminium. The settings I used are the same as for cast Al of the same thickness, in this case 110A, 70% negative balance, 110 Hz, square wave. Shielding gas is Ar and the TIG-welder is a German EWM inverter with foot control and an air cooled torch. The (sharp pointed) tungsten is grey coded and the rod contents are minimum 90%Mg, 0,1%Si, 0,7%Zn and the rest Al. If the preparations are right, it is almost like welding Al. If not, there is a lot of splatter and smoke. When that occur (and it does), it is just a matter of starting all over with grinding and stainless brushes, then another pre-heating and so on.

 

These photos show the parts after a first degreasing and brushing, then after the first stages of welding and rough grinding, but before final machine work and final filling/detail welding. If I had aimed for a perfect look, there would have been much more pre-grinding and more extensive welding before finishing, polishing and so on. However, in this case I have opted for function, not looks. Also, to show how relatively easy magnesium welding can be done with the right equipment and some patience.

 

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