Welding Tips and Tricks

Long story short, trying to decide the ideal TIG filler material for fixing a busted transmission mount ear as well as a planetary gear housing crack both cast aluminum. Currently using 4043 filler rod and wondering if there is a better alternative. If the information helps, it's an older aircooled Porsche casting. It's aluminum but what "kind" of aluminum is to be determined really... I know they used to make a lot of magnesium parts so is it possible to be high enough in Mg to make 4043 no good?

From what I've gathered 5356 alloy has some magnesium in it and 4043 has some silicon in it. As I said before, 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 so that's what I began with.

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 in this application. Both seem equally hard to locate also BTW. My local welding supply told me on the phone I couldn't get a pound of either and that I'd need to get 10#. I said "OK" and then when I showed up, he made his phone call and told me min. order was 40lbs @ 6 bucks a pound

I said "hold on, I need to figure some things out before I ever dedicate to that much filler rod"

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... I'm causing porosity in nearby areas trying to wet out the dab I'm currently hovering over so it seems like a lower melting point and less base metal dilution would be of help here.

Thanks for any advice, I know this is a whopper of a first introduction post

I use 4943 over 4043 exclusively now. I use either 5356 or 4943 for cast, preferring 5356 if the cast will be polished (not likely in your application). I’ve seen others remark that 4047 is very good for cast, and I’ve got some, just haven’t had a chance to use it.

When I do weld motorcycle cases, I use a very low AC Balance (55-65%) for more cleaning action, a higher frequency (usually 150-175) and I ease into the puddle. Cast typically has a lot of trapped air pockets and these expand when welding nearby. You’ll get “blisters” if you loiter around with the arc. I preheat, chemically clean, then stainless brush scrub the area, then Acetone wipe, then weld. This helps a lot with drawing out the porosity and eliminating the trapped schmutz in the ally cases. I use a thin wire for root pass, then reverse directions with a larger wire. Cool between passes, scrub with stainless brush between passes, and keep an eye out for overheating the cases.

I buy 4943 readily online from www.weldingsuppliesfromioc.com by the pound or more. My LWS has also taken to stocking it since I asked them to order some in. Good guys, they are very helpful.

Hope that helps-

Baker's Gas & Welding will sell you 10lb boxes of TIG rod, you just have to send them an email. Unless they recently put it up on their website.

Oscar wrote:Baker's Gas & Welding will sell you 10lb boxes of TIG rod, you just have to send them an email. Unless they recently put it up on their website.

That's where I got mine a year or so ago, at $6 lb for 10 lb

I got a free 10 lb "sample" from Hobart of their 4943 once.

I asked for a 1 lb sample....

Still have 80% of the box, it's been almost 2 years, lol.

Check with them if they will send you a sample, they also sent me some oddball alloy for some oddball cast piece I was going to weld but never did, because it never broke again, or wait, no it did, and I fixed it with that.

Anyways, ask Hobart if they can sample it for you, if they still offer it.

I can't remember what I've used on cast stuff, I only have 4043, 5356 and 4943 on the shelf, and I haven't had a cast aluminum piece I couldn't fix.

I got a 1# tube from arczone.com not too log ago. Not sure if the price was good they were just the only place I could find 1#.

Funny enough I talked with my LWS and they said they were having a hard time tracking it down. The arc zone stuff showed up then a day or two later my LWS dropped off a free 10# box of 1/8"


For me with cast I find the key is to clean the surface very well then go over it with the torch very lightly (like hardly even puddling) to boil a bunch of crap out. Then brush all that smoo off and rinse and repeat till I can get a small puddle with no more smoo and then I'll start adding filler.

Pretty vague description but I hope it helps. Pretty sure I picked that tehnique up from one of Jody's videos he did on a cast outboard boost engine repair he did.

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I have a lot of experience building Porsche engines and transmissions. Which car are you working on. All of the heads from 356s thru 911 are aluminum and easily welded, with a lot of preheat. Most headwork required and oven, beadblasting and a lot of cleaning.

356 engine cases are aluminum and can be repaired. Bore alignment is an issue afterwards

911 engine cases thru 1973 (2.4L) are aluminum and can be repaired. Bore alignment is an issue afterwards

911 engine cases from 1974 - 1977 are magnesium and to the best of my knowledge are rarely repaired. They will burn quite nicely, ask me how I know.

356 transmissions are aluminum and can be repaired. Bore alignment is not as critical in transmissions

911 transmissions are different. Certainly the early ones were weldable aluminum. I just don't know about the newer ones G50 etc.

4043 was my choice on all the jobs I did.