TOPIC:

Went back and had another look - I don't think I have anything to worry about. However, I'm waiting on a new welder and when it gets here I'll probably put the bracing it just for piece of mind.
Here's a photo of the join next to the shock mounts for Scirocco - looks a bit better from this angle. I also added a couple of better photos of the thin spot.

 

 

 


And both sides after cleaning up the welds:

 

 

OK, I'm going back and forward on this one... 

Probably the best option is the bracing suggested by kzstreetfighter71. The problem with this is I need to get the OK from the guy doing the MOT and am worried he'll either say it is unnecessary or he'll go in the other direction and want to do too much.
To avoid any potential hassle I'd like to just cut the bracket off and build up the tube with the tig welder. I have a couple of questions for the guys out there that know their metallurgy:

• Given that all the area I will be building up was in the HAZ of a different weld, will I weaken the tube at all?
• Should I stick to short beads (~2-3cm long) and let the frame cool completely before the next one?
• If I build the tube back up to its original wall thickness, will it be as strong as it was before (assuming I get good penetration)? 

Basically, the real question is whether Wookie58 is right - will I do more harm than good building it back up?

This may be a better question for a welding forum - but I trust the knowledge and experience here.

IMHO - I think you are over thinking it.  With that gusset in place, the thinner area is not going to contribute to a failure.  The overall area with the gusset is now stronger than it was stock.  But then again, my opinion is worth exactly what you paid for it...

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But then again, my opinion is worth exactly what you paid for it...

It's worth a bit more than that You've got a lot more experience working with metal than I do!

Nothing to worry about with any of that welding.

I’m so jealous of those braze welds! I would love to do that to my frame, and then file/sand everything to smooth fillets, and repaint it. 

I agree with he general consensus, the bracing is more than strong enough on that section and if you were to put that wee cap on the tube under that bracket it would pass any inspection. Ill be doing something similar with my Z1b soon enough fixing about 20 years of injustice to try and bring it back so a sense of its self, ill be using half a 30mm O.D  x 1.5mm tubing on inside and lower section of the frame tubing to strengthen but be fairly invisible in the same section of frame you are working on. 

After a lot of second guessing and ignoring advice from people that know better I have decided to put a slightly longer square piece along the top of the tube with a couple of short threaded bungs for fitting the seat and tail mounts. I'll make up some aluminium spacers to slot over the bungs so I can set the height of the fittings. This has the added bonus of freeing up some space under the seat for electronics (would have been taken up by the seat mounts). It also completely covers an area on the tube that needed repairing after the PO was a bit heavy handed with the grinder.

Probably going a bit overboard, but I will feel better when I'm on the road

I just chucked some spacers on as placeholders for the photo:
 

Lateral thinking at 130% there bud! you could probably hang a truck off that tail section when its done.

Ich beschreibe es mal in einem unmissverständlichem Deutsch. Das was du da vor hast an ungeprüften/unzertifizierten Scheißarbeiten, wird dir kein fachkundiger TÜV Sachverständiger auch nur ansatzweise technisch abnehmen!!! Die Festigkeit des hinteren Rahmendreiecks ist mehr als ausreichend und bedarf keiner "Verschlimmbesserung" durch noch mehr Schweißarbeiten (Hitzeeintrag/heat stress). Alles was vor der orginalen hinteren Federbeinaufnahme verändert oder geschweißt wird ist ein absolutes "NO GO" in good old Germany.

wrote:

Ich beschreibe es mal in einem unmissverständlichem Deutsch. Das was du da vor hast an ungeprüften/unzertifizierten Scheißarbeiten, wird dir kein fachkundiger TÜV Sachverständiger auch nur ansatzweise technisch abnehmen!!! Die Festigkeit des hinteren Rahmendreiecks ist mehr als ausreichend und bedarf keiner "Verschlimmbesserung" durch noch mehr Schweißarbeiten (Hitzeeintrag/heat stress). Alles was vor der orginalen hinteren Federbeinaufnahme verändert oder geschweißt wird ist ein absolutes "NO GO" in good old Germany.

That's why I had someone weld the rear shock mounts who will also get it through the MOT for me. I didn't (and won't) do anything that hasn't been given the OK. I also won't be welding the square profile in the picture - that will be going to a certified welder as it is a bit more than a "simple bracket" which I have been given the OK to weld.

Don't worry - I made sure it's somebody elses problem if it doesn't get certified

Hah, look at that. You said you wrote in german so you wouldn't be misunderstood - and I think I misunderstood

Don't worry, I won't build up the side of the tube - too much heat and I have too little knowledge of what effect that will have. The bracket in my last photo should be fine, but as I said, it will also be going to someone who knows what they're doing. Waiting on word from the guy who is organising the MOT and if he says no then the old bracket will just be going back on.