Is it a crack or ???

[orezok]

I was airing up the tires on my B7800 and notices this on my rear wheel. Thoughts?

 

[jones6780]

All I see is a weld with a little undercut. Point to what you see.

 

[orezok]

All I see is a weld with a little undercut. Point to what you see.

Heres a better image with annotation. The other 5 areas the paint is smooth over this area.

 

[oosik]

I see a spot where somebody welded on the rim to make a repair. Rust or ??? Is this tire going flat on you? Soapy water on this spot to check for air leaks. If it's leaking here - instal a tube. Otherwise - maybe a new core in the stem.

The other five areas - ???? There are six "welded tabs" on this rim - ??? Check them all with soapy water. If this tire is already tubed - could be that one of the welded tabs is sharp on the inside and has cut the tube.

 

[radios1]

this pitted weld is the kind you get if you don't clean the metal properly first.

 

[orezok]

I see a spot where somebody welded on the rim to make a repair. Original factory weld Rust or ??? Is this tire going flat on you? Soapy water on this spot to check for air leaks. If it's leaking here - instal a tube. Otherwise - maybe a new core in the stem.

The other five areas - ???? There are six "welded tabs" on this rim - ??? No, three on each wheel Check them all with soapy water. No leaks yet. If this tire is already tubed - could be that one of the welded tabs is sharp on the inside and has cut the tube.

. I dont think the crack goes through the rim, just between the rim and the hub. I plan to chemically paint remove some of the paint to see the virgin metal, but I didnt want to do that until the comments were received.

 

[5030]

All I see is a porous weld caused by mis-application of a MIG gun. If it was mine, I'd gouge out the weld and re-weld it (of course removing the tire and tube first).

 

[rScotty]

Heres a better image with annotation. The other 5 areas the paint is smooth over this area.

View attachment 622906

With a picture of the whole wheel shiowing all the welds I could help more. As is, I'm not understanding exactly where on the rear wheel this weld is? and why there are another five similar welds? But if those six welds are part of the normal wheel manufacture and if they are better.... and if they don't involve the tire rim or tube area too much..... then on something light like the B7800 I'd probably just fill those pin holes in with paint and ignore. And here is why...

What I'm seeing is what is called "porosity". When the pin holes are round like that it is most likely caused by poor welding technique instead of contamination.
Sure it could be the result of trying to weld over contamination.... or even of welding something that is wet with water....., but usually when the bubbles look like that it is from welding too hot or with the arc the wrong length. Looking at that weld, It's kinda undercut as well, so I'd say too hot and he/she were trying to keep the arc a little too short.

Both of those are the kind of poor welding mistakes you see in production runs where they are trying to weld as quickly as possible. Too hot, too short, too fast.
You can grind it out and reweld, but that's a hassle, and it probably isn't necessary. Especially if the rest of the wheel is good. Truth is that most welds have some porosity, even if it is microscopic. That much in the photo is a bit too much, but porosity doesn't necessarily mean the weld is weak - just that it could have been much better.
A porous weld without cracking is still stronger than the adjoining area that doesn't have any weld at all.

BTW, If you ever do want to make crappy welds like that look good, it's easy to do by just grinding out the porosity and welding it again.
It's even easier when doing oxy/acetylene or TIG welding and there's a reason you don't often see porosity with oxy/acetylene or TIG welds. That's because using those techniques you can go back and remelt the weld itself as deep as you want. Then, by playing with the heat a bit and chasing the molten metal around you can cause it to flow & harden with a smooth surface without adding additional metal....or at least not much...just enough to make the surface smooth.
rScotty

 

[5030]

I would not be at all surprised if those welds are robotically applied.

 

[Egon]

Angle grinder and new weld would work.