Calling all fabricators

[993Speedster]

This question pertains to repairs and welding... in specific a transmission case for my 964. Posting this question here as this part of the forum has no doubt the largest number of modified vehicles and the rarity of some older parts necessitates fixing VS replacing sometimes as things just aren't available anymore.

Long story short; what's the metallurgy like for Porsche's air cooled castings? Trying to decide the ideal TIG filler material for a G64/01 as I'm fixing a busted transmission mount ear as well as a planetary gear housing crack. Currently using 4043 filler rod.

From what I understand 5356 alloy has some magnesium in it and 4043 has some silicon in it. I don't know if these aluminum castings have any Mg in them but most have said 4043 is better for cast materials as it resists cracking while cooling.

I also understand 4047 has higher silicon content and wets out easier with slightly lower melting temp. This is supposed to be beneficial for porosity on cast stuff as it doesn't pull up as much contaminants from the base metal (something I'm DEFINITELY running into). So I'm considering trying some of the 4047

But then we have the newest proprietary blend from Hobart... the 4943 which is supposedly supposed to have same benefits of 4047 vs 4043 but "better"? It's blend is also secret so who knows really if it'd be any leg up on the 4047.

Anyone having made successful repairs to engine cases, transmission cases, or any other cast aluminum Porsche parts; I'd love to hear you procedure for making it not look like total crap. I've already tried carbide burr, cook/preheat with torch, high % A/C balance for more cleaning action, the works...

[Jim2]

I had no issue welding on the outside of a 964 trans. Perhaps you are welding on the inside? Oil impregnates microscopic pores in cast alum and wreaks havoc until it's- all-burnt-out.

[GJF]

All aluminum rod has some amount of magnesium. Use 4643 and Instead of preheating with a torch, stick the trans case in an oven for an hour at 400 degrees before welding.

[993Speedster]

Originally Posted by Jim2

I had no issue welding on the outside of a 964 trans. Perhaps you are welding on the inside? Oil impregnates microscopic pores in cast alum and wreaks havoc until it's- all-burnt-out.

It was previously repaired and poorly so there's porosity and oil that's been leaking through to the outside through the voids. Now that I've had several takes at it, the planetary gearset housing is actually welding better. I did also switch to a larger 1/8" tungsten that can handle the heat while still keeping an acceptable sized point and focused arc.

Originally Posted by GJF

All aluminum rod has some amount of magnesium. Use 4643 and Instead of preheating with a torch, stick the trans case in an oven for an hour at 400 degrees before welding.

The one part that's removed currently and is "oven sized" would be the planetary gearset housing and it's pretty much done as of now. Ready to be machined down on the flange. The rest of the trans is still very much still put together so an oven isn't quite an option. I think I'm going to use a high temp heat-gun on the rest of the trans so the heat isn't so focused and intense to where I can just roast that spot dry as a bone.

[993Speedster]

This is the "before" situation in case there was any curiosity as to what happened and why it's so difficult to weld. It hurts my F'ing soul to think someone did this and said "fixed". Literally a scab of silicone the size your hand covering this catastrophe...

[Jim2]

Uncertain how much torch time you have doing aluminum repairs but it's imperative that the region where the weld takes place is clean, as in, medically clean. Not one black spec of grease, sealant, or oxidized aluminum surface. My cleaning time for welding that ear would easily be an hour or more. Even then oil seeping from porosity will have to be cooked out with a torch and then the area recleaned.

I don't envy you having to re-repair that mess.

[full quack]

Really??? A junk yard trans case can't be that much $.
Without a descent milling machine and trim work, there is no way you are going to get a true/flat/straight mounting surface.
My .02 worth.
Mark