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HeadExam

Magnesium Repair

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I am in a quandary about two repairs on a chainsaw made from cast magnesium. The first repair is a small chip in the side of the airbox and I have been advised that by heating the area sufficiently to melt a aluminum flux core rod I could build up the area and sand it some, I would need some tin dams to keep the aluminum in place while cooling, another option was to use a two part epoxy repair. I have concerns that the epoxy repair would not hold on this particular area so I am leaning towards the aluminum weld. I have nice torch, I just am not sure in my ability to accomplish this type of repair. Te second repair is the petrol cover and it has been struck with enough force to have possibly created a crack in the interior of the tank cover. Whether it has or not I also have been advised tat by sanding it bare and using an epoxy patch would repair the defect, but again, I am not satisfied in this type of repair. I cannot get another gasket for the tank cover so if it was removed I would have to use a RTV type sealer, but I was thinking that the repair should involve removing the tank and using a vise to remove the dent and possibly using a solder or aluminum wel on the crack. I can buy the complete tank and cover in good used order for 35 US, so I am actually leaning towards this direction.

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I would be a bit  carefull there  I remember heating a magnesium wheel up back in the 80s and it caught light and we could not put it out it was a bit like those lithium battery’s you get now when they ignite they just burn and burn

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I'm neither a welder nor a metallurgist but I'm under the impression that magnesium (or may be not a particular  alloy of) is flammable so how much heat can be applied? Also can aluminium and magnesium alloy be mixed?

To explain my thoughts on magnesium being flammable, many years ago the UK made Ferguson tractors had a magnesium alloy gearbox housing and if one of those tractors was unfortunate to be in a barn fire the result would be a front and  a back and a pile of gear wheels - the gearbox casing being entirely vapourised.

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Supposedly a person that is skilled in tig welding can weld magnesium, also using a torch to heat the magnesium just hot enough to melt aluminum, but not hot enough to ignite the magnesium provides superior repairs, However, I would have to know and be able to gauge what that temperature is to accomplish the aluminum repair and I am not sure I want to attempt it at all and possibly lose the saw (and shop). The saw is a Homelite 2000 made in 1968 and it has 115cc. It is a saw that while not rare is very hard to find in this condition internally. I have made the decision to buy the used tank and cover. but I am still mulling over the air box repair. Can anyone give me an opinion as to how strong the JB Weld/epoxy repair would be on the half moon area? Thanks, Alain

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Difficult to gauge just how wide that lip is but would it be possible to drill some fine holes to accept panel pins, or what ever they are called your side of the pond , and use them as a key for the JB weld?

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29 minutes ago, Wristpin said:

Difficult to gauge just how wide that lip is but would it be possible to drill some fine holes to accept panel pins, or what ever they are called your side of the pond , and use them as a key for the JB weld?

That is sort of what I was thinking, however I just thought about drilling holes to let the epoxy go into the magnesium. The panel pin (small brad nails?) idea is superb and that is exactly what I will do. Thank you so much for the suggestion. I can drill and putty, but I'm not willing to risk the possibility of starting a fire that can't be extinguished.

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I have recently been researching restoration of magnesium alloys in readiness to restore the wheels on a Ferrari and I can tell you it is a minefield of does and don'ts because of fire risk and instant corrosion, I would avoid welding if you can and use either fire spring roll pins or fine threaded bar into a series of tapped holes as a means of coping with expansion of the alloy when warm in use. If you want to go down the metal repair route with sufficient pins in place you could use soft lead with a plasticine dam either side to retain it whilst cooling.

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5 hours ago, expeatfarmer said:

I have recently been researching restoration of magnesium alloys in readiness to restore the wheels on a Ferrari and I can tell you it is a minefield of does and don'ts because of fire risk and instant corrosion, I would avoid welding if you can and use either fire spring roll pins or fine threaded bar into a series of tapped holes as a means of coping with expansion of the alloy when warm in use. If you want to go down the metal repair route with sufficient pins in place you could use soft lead with a plasticine dam either side to retain it whilst cooling.

While the airbox may get warm it should not experience any kind of high heat whatsoever, but duly noted. The repair is very thin, so I think drilling and epoxying panel pins for support then using double wall dam to contain the epoxy wall around the pins may be my safest and strongest option, but any opinions are more than welcome.

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I can only agree with everyone on here that any application of heat by flame is a 'No No' with regard to the risks. Tank Dent is sorted I believe, by replacement :thumbs: .

I would look to use a good Metal Repair Epoxy and 'Dam' the inside wall edge of the Lip with a piece of nylon or shaped Beeswax to which the Epoxy will not adhere.

The bonding faces should only need a clean with a Dremel type drill with a Burr Tool to rough it up-

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Thickness of the Lip look's only about 3/32" , if you have a small enough drill Bit, then small indentations at either end and at an angle shown should be more than is required to provide a Key/anchor for the resin-

 

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Difficult to say how the damage was caused, but I'm sure it won't reoccur  in your possession.

Metal Repair Epoxys are very good (not the 5 minute setting ones) and I've even machined them with very good results. 

Regards.          

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Thanks Richard. The help given here has boosted my confidence in the epoxy repair and tank replacement decision. After drilling the holes, are you saying that I should insert a metal pin in the holes or let the epoxy bond into the holes as support?

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16 hours ago, HeadExam said:

Thanks Richard. The help given here has boosted my confidence in the epoxy repair and tank replacement decision. After drilling the holes, are you saying that I should insert a metal pin in the holes or let the epoxy bond into the holes as support?

 

Hi Alain, Well, you can either just apply the Epoxy after making the shallow holes and roughing the surface. Or you can drill a little bit deeper and 'Spring' a piece of thin wire in and between the holes so it sits lower than the Lip height and build up with Epoxy around it for added strength. You can then trim it to shape before painting.

Regards. 

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