Welding cast aluminum

[Nikolai]

I found a crack on the front differential housing of my Polaris RZR. It’s slightly depressed like a rock got wedged between it and the frame and pressure cracked it. It is NOT cracked all the way thru, holds fluid just fine, no idea how long it’s been that way. I pull it apart every year for inspection. I was running a tap in the mounting holes to clean them up when I noticed it.

I own a Miller Diversion 165. I’m not a great welder by any means but I can lay a decent bead.

The diff housing is cast aluminum.

1. Can I run multiple beads over the area the reinforce it and make it a permanent fix?

2. If I weld it, do I risk even worse cracking down the road? Or other problems I’m not thinking about?

3. If it is weldable, what is the preferred filler rod for repair cast aluminum? I have 4043 in 1/16 and 3/32 but I can buy others.

Lastly, a used case half on eBay isn’t that much, $250-$300 but with a wife and kids and stupid high cost of living I would like to save my money and try to repair it if I can. Only if it will be a permanent fix though.

Appreciate any help/advice.

[Bushytails]

Is it a crack, or is it a casting defect that has been there since new?

[Nikolai]

Almost positive it’s a crack. I’ve had it apart every year for the last 5 years and can’t believe I wouldn’t have noticed it before now, especially since I run the tap down the mounting holes each time. It also has a slight depression when you run your finger across it. That said, I am not 100% positive.

[Bushytails]

My gut feeling is to go with the old expression "if it ain't broke..."

[ryanjones2150]

So what happens if it does fail? Does something fall off, like catastrophic failure, or does it just start leaking stuff?

I agree, looks like a crack. I’ve had excellent luck with cast aluminum repairs, but you don’t just want to run a bead over the crack, it’ll just keep cracking. You’ll need to burr it out. Once you burr it out and start welding, you’ll find the end of the crack.

I like 4943 on cast aluminum. Had good experience with that alloy over 4043.

My bigger concern is your machine is not very big and does not have a good duty cycle. I’m saying that without knowing how thick this casting is, but once you start, you want to keep going so it doesn’t cool quickly.

And that part is pretty dirty. You’ll want to clean it really well. Maybe even take it to a machine shop and have them run it through their parts washer.

You have some things to consider, but do not consider just welding over the cracks.

[Nikolai]

If it were to break open while riding and fill with water/mud then it destroys the internal parts at a replacement cost of about $1,000. Plus the hassle of removing it in the field and then trying to get back to the truck in 2WD.

The casting is not very thick in that area, feels like 1/8 or so, it’s definitely not 3/16.

I scrubbed the case with soapy water, took a carbide bit and knocked down high spots and grooved it a little bit and then emery cloth over it. It looks a lot better but I still don’t think it’s just a casting flaw. I’m putting die penetrant over it later today.


Is it best practice to start welding past the crack, and then weld continuously past the other end of the crack and add a little more filler at the end before stopping? I’ve been trying to watch all the YouTube videos I can.

[aametalmaster]

I welded aluminum wheels for years. I found the best thing for cracks is cut them completely out with a wiz wheel then fill the crack with filler from the process of your choice. I prefer mig with a spool gun but now I use a tig because it’s what I have. The aluminum has to be clean.

[ryanjones2150]

You can use crack detecting die and developer if you want, but it’s just another thing you’ll have to clean off.

You can use soapy water if you want, but you really need some sort of solvent. Cast metals are porous and you need to dissolve the nasties if you can, then deal with the aluminum oxide. My solvent of choice is non-chlorinated brake cleaner.

Like Bob said, you need to cut the crack out. I prefer a carbide burr. And like I told you in my first post, welding over a crack is a bad idea. You have to find the ends of the cracks and stop drill them or burr it out. Once you start welding, you’ll find the end if you didn’t stop drill it...or you better hope so...but it’s critical that you find the end of that crack. And it may go in several directions.

You’re seeing a prime example of why these sorts of repairs are expensive! You may be money ahead to just buy the new part if it’s just a couple hundred bucks. If it was mine, I’d fix it. By the sounds of it, having it fail on you in the field would suck.

[Nikolai]

I appreciate the feedback. I did die penetrant 2 times just to be sure and it is not cracked. Now whether it’s always been that way and I didn’t notice, or something put a crack in just the outside I’m not sure. If it was indeed cracked then it sounds like buying the case half would have been the way to go.

[ryanjones2150]

Did you spray the developer on there or just the die?

[MMW]

Just my take. In the amount of time for everyone to post you could of welded it up. It's not leaking now so any beads you run will be reinforcing it. If it fails, ie starts leaking, it will not fill up with mud and water unless a big chunk just falls off. Most likely it would just start to weep if anything. I say weld it and move on. Your machine should be capable just take your time to let it puddle before adding rod. You may have to weld, grind out and weld again to remove crap. Don't forget to remove seals before welding.

[ryanjones2150]

You’ll find if it’s cracked that way for sure.