Welding Magnesium Crankcase

[911GP]

Hello,

I have a small crack in my crankcase at the bottom of the engine where a clamping bolt boss has cracked. 1973 Magnesium case.

Can anybody recommend a method to address this, taking care not to warp the case etc?

Thanks
Gitesh

[911hillclimber]

Chat to Rob Frost, see his engine thread below yours.

[RobFrost]

It's tricky. I bought some magnesium ingots, practiced a lot, made some home made flux and then did it.

The flux prevents the back of the weld and surrounding areas absorbing atmospheric gases and/or catching fire.

Whilst practicing one of the things I welded instantaneously entirely decomposed into a blob of molten metal! You don't want to do that to your engine case!

You need magnesium filler rods, AZ92A. They're £350 a kg but you'll only need one rod. I have one you can have.

You need to spend a lot of time cleaning and clean the rods too, with wire wool followed by acetone until it's shiny and bright.

Grind out the crack and I welded it on AC at about 120 amps I think it was.

Ideally bake the engine to 200°C first to reduce the risk of distortion. I kept mine hot with a blowtorch.

The casting contains impurities, possibly oil, which has soaked into the case over time, which turn to gas and make the weld porous as you weld. Controlling that was the trickiest part of it. Whereas the magnesium from the rod has no such problems.

After every burst of the torch you will need to reclean the weld and the rod. The oxide is problematic because it forms a barrier to the flow and melts at a higher temperature than the magnesium itself.

The recommendation is to bake out any welding stresses at 200°C for 1-2 hours afterwards.

I used a very long run-on on the Argon, which I could use to prevent any fire developing. Thankfully the heat dissipates quickly on such a large casting, and the oxide layer suppresses fire to a degree.

If a significant fire develops then you're in trouble because it can't be extinguished with water, sand or CO2.

Where are you based? I reckon Bob at the machine shop in Hinckley would be worth asking if he could do this for you or help.

I am not a confident tig welder so I wouldn't want to risk working on anybody else's case myself. It's okay if I wreck my own stuff.

Sent from my SM-S918B using Tapatalk

[911hillclimber]

The above would make me go to a specialist!
In the West Midlands there are several.

I've had magnesium (from the 1970's) welded before at Jamisen's up in York, but that was 10 years ago.

[911GP]

Hi Rob, thank you for your erudite reply. You have far more skill than I do so I will be looking to get the work done. I too had heard that the mag cases can absorb oil, which needs to be thoroughly cleaned off prior to welding.

Hi Graham, thank you for Jamisen’s recommendation. I called them and they seem very good but York is a looonnngggg way for me so will need some planning. Incidentally, they mentioned they would TIG weld to keep the heat down (they do not offer laser welding).

Has anybody tried laser welding on Mag cases?

Kind regards
Gitesh

[Yellow491]

Bob hall concept racing at ross on wye,has a proper pulsing tig.
He has welded a few tuthill cases over the years.

[911GP]

Thank you for the contact.

[STUTTGART]

Hi Gitesh,
RE your welding question. You mention being a long way from York, I assume you're in the south east ? There is a company called EMP engineering in Havant Hampshire, who may be worth contacting regarding laser welding , which would be the best/ safest way to go. www.e-m-p.biz/classic-cars/.

[911GP]

Thank you. Appreciate the help.