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Welding a magnesium deck?

7806 Views 40 Replies 11 Participants Last post by  Yard Nazi
I have a deck from a 1966 Toro Whirlwind that looks like it was used as a rock crusher. There are lots of small star cracks and holes but my main concern is a couple cracks near the left rear wheel. There's one about 3" long and a smaller crack across the rib that the handlebar attaches to. The small crack doesn't appear to go all they way through. Now I assume welding is the best fix but I believe the deck is magnesium. I think so for several reasons:

- 1966 literature says the deck is magnesium
- It feels too light for aluminum - the deck only weighs 6 pounds!
- Magnesium about 2/3 the density of aluminum. I have the same deck in aluminum that weighs 9 pounds, so the numbers correspond nicely.

Do you think welding is possible here? I think it would be tough to clean the crack well and also the deck is really thin. And i heard magnesium rods are crazy expensive so I can imagine the cost. How would you fix it if welding isn't an option?

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cheap solution, drill a small hole at the top of the crack (to stop it spreading)-then fill in the crack with JBWeld use c lamps to hold the desk flush and sand the JB weld smooth once it dries.
PS...what did you strip the deck with??-it looks amazing!!
you can weld magnesium no problem. It's getting the magnesium sticks that are harder. Try a custom bike shop if you have one in your area. The shops that fix/work on old bikes will likely have the mag. sticks and could weld it for you. Otherwise I would go with what GTP suggests and just JB it.
Good Luck

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Here's how I cleaned it, an hour of power tools and several hours of hand work. Wire Technology Electronic device Electrical wiring Machine
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cheap solution, drill a small hole at the top of the crack (to stop it spreading)-then fill in the crack with JBWeld use c lamps to hold the desk flush and sand the JB weld smooth once it dries.
This was my original plan. I've done it in the past and the crack has usually come back. But most cracks I've fixed we're worse than this one. The JB Weld would have to hold the parts flush. Maybe I can somehow keep the parts aligned mechanically and then fill the crack with epoxy.

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Wow, that deck got banged up quite a lot! I was wondering what you were planning for this missing chunk out of the right side:

If it all proves to be too much of a hassle, I have a mint '66 deck with no cracks or blemishes whatsoever, just needs someone's amateur paint job stripped. It's a 21" deck, so you would need a 21" s-blade to go with it, but I know I have one of those on hand as well. I don't know if you would want to change to a 21" deck, but it's an option. I have a perfect 19" deck....the one from Al, actually....that I have not used yet, but that is from 1970 and does not have the Trimit casting. The '66 21" does. And that is a mag deck, where the later 19" is aluminum. (My plan is to likely use the 19" deck to replace the one on the 19" Whirlwind that I got from Scrible, as the deck on that one has some significant cracks.

Anyhow, if you decide you need the '66 21" deck and blade, the shipping wouldn't be bad because the weight is low. :fing32:
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I've patched missing areas like that before and it shouldn't be a big problem. It's about a 1" x 2" area and it's mostly hidden behind the chute. It's not structural so it just needs to stay in place. My plan is to make a piece of aluminum that fits the missing area, and then JB Weld it with some mesh that wraps onto the flat part of the deck for reinforcement.

I don't think a replacement deck will be necessary but I'll let you know if I change my mind. As long as I can get that crack to stay together, it should be fixable. I've seen worse. There is a LOT of damage that you can't see in the pics but it's mostly stuff that can just be filled in and smoothed.

I'm thinking I'll probably skip the welding risk and just use epoxy. The crack closes with about 10 pounds of pressure. Should I grind out/remove some material to help it close easier? Also I have the regular JB Weld and some PC-7 epoxy that's like a putty. Which do you guys think would fix the crack better?
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I think I would remove a small amount of material to relieve a little pressure there....just my opinion.

For patching, I generally use Plastic Aluminum or a different brand equivalent. Worked fine for the small trim fastener holes in the Caprice, too.
Hi! I have used JB Weld for a number of small projects with much success, however for a crack that large I am not sure how well it would hold up. If the mower is going to be used as a daily driver then in my opinion, welding is the way to go. The small star cracks can be filled with JB Weld. I recently had a mag deck welded, just one crack, and it cost me $30.00 and was done by a large welding shop that does a lot of custom railings and iron stairs and stuff. You can be sure if it is magnesium if you can scrape a few filings from an inconspicous place under the deck and then see if they will burn. Bill
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The only way to fix this is to weld it. Jb wont hold up, look at how much work you put in.
If you were closer I could do it for you. MG is easy to weld, take it to a local fabrication shop and ask if they will do it for you.
I already ground the crack open and put some epoxy on. :hide: Should I take it off and see if I can find a welder or see how it holds?

Here's what it looked like before epoxy:
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Luckily the PC-7 epoxy I used sets slowly and can be washed off with soap and water so I'm back to square one. It now looks like the picture again. A welder could fill that crack right? It was pretty greasy in there so I really HAD to grind it that much to get it clean and let the parts fit together well.
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We have some stuff called quick bond. It has a stiffener for steel and aluminum. Not sure if it would work on magnesium.

I hate to say this, and I may be one of the bigger Toro fans here, but that deck is rough. It may be beyond repair. It is always a tough question to answer, especially on a rare bird like that.

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Hi! A good welder can repair that and after you grind down the repair and finish and paint it you will never know it was there. The weld will be stronger than the deck. Bill
Even with that gap? Measures about 1/8" to 3/16". I beveled it so there's more surface area for the weld. I supposed they would run a pass on each side and then one down the middle? That would be great if they could do that!

I hope I can save it podor. If this crack can be fixed, the rest I can handle. It's rough for sure but that will just make me feel even better when it is finally done!
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Yes, get it zaped up. Glue is for fixing shoes.
Awesome, I'll see if I can call around tomorrow and see if anyone can do this. Would you guys do anything to the crack across that rib or just let the, clean/grind it?

Also, I assume they can't do much about this area (I don't have the missing piece)?

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"The only way to fix this is to weld it. Jb wont hold up"


Walt Conner
Hi! Any missing pieces would need donor pieces from another deck. If you have another broken mag deck or could find one you could cut it up and fabricate a patch. Bill
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