Looking for informed opinions to compare seat mount joint

They look like pretty good welds to me, but the only way to know for sure would be to test either destructively or if you estimated the force that the original rivets could withstand, you could test non-destructively to that level.

My intuition tells me that even if the welds failed at that location, the other 3 mounting points would likely be strong enough to keep the seat in place, however, you would need to test this to be sure.

How are the other 3 mounting points modified? Is the rear outboard mount welded as well?

There was another thread that became controversial because the OP intended to sell brackets to move the seat and was not going to perform any testing or other analysis. He got angry because we brought up some of the liability issues. I don't have any issue with someone modifying their own car as long as they are aware of the risks; I don't believe anyone should consider selling a modification without doing the analysis and testing to make sure it is a safe product.

That is my opinion based my education (mechanical and materials engineering) and my prior experience working for a vehicle (large truck) manufacturer.

 

It looks like a decent weld, but it's impossible to judge the strength. Was drilling new holes and bolting it not an option?

 

I don't think there is enough clearance to use a bolt and still allow the inner rail to slide past the outer rail. I think that is why the original seat uses a low head rivet.

I think the choice to rivet instead of weld the original is primarily an economic one; its faster to swage the two rivets than weld - you could spot weld, but that wouldn't be as strong as the rivets.

 

Too small for my old eyes to see.

 

Then welding it is. It looks to me like you've done a good job, but I'm not an expert. My thinking with the bolts was that there'd be no question of liability. Unfortunately, the current legal climate makes any kind of safety modification risky.

 

Harder to tell, but probably ok.

I had forgotten how close the outboard rail is to the top of the bolt. That what makes it so difficult to lower the seat - there is almost no clearance at the outboard bracket, so any mod to lower the seat has to involve the seat frame itself.

One thought that I had is that you could actually "tie" the seat frame to the bracket on both sides using 1/8' aircraft cable (aka wire rope). You would probably need to drill a 1/8" dia hole in the bracket and loop the cable through, then loop around the seat rail(s). You can fasten the loop(s) of the cable using special wire rope fittings or swage the loops if you have the tool to do it (I actually have one). The aircraft cable would restrain the seat from lifting up at the rear if the welds did fail in an accident. Probably overkill though.

 

I do metal fabrication & design for a living

I only have two concerns abut the weld:
1 - Does it has good penetration, most recreational welders tend to turn the heat down a little to much on the thin stuff for fear of burning through.

2 - Is the rail a heat treatable alloy? If so the welding will create an extremely hard and brittle boundary where the base metal was heated above the critical temperature.
You can check this by striking with cold chisel and hammer to try to crack it, or try to test the harness of the base metal ,weld, and interface with a scribe.

If it is hard, the area could be tempered to a lower hardness. I have done this to thin (.10") sections with a propane torch, but using mapp gas or adding oxygen works much better, or an oxy/acetylene torch is best

I would not have a problem with the weld otherwise