To weld or not to weld?

[morris]

After a ride this morning I noticed that the frame from the SA had cracked.
The left downtube  ripped itself loose from the headstock. Looks like I had a lucky escape. If the other downtube had followed I don't think I would be sitting here typing this...
I'm pretty sure that the width of the front engine plates is to blame. The pictures show that both cracked ends of the downtube are out of line. When I loosened the engine plate studs, it all jumped in place. This leads me to think that the tubes where forcibly pulled together and one of them let go...
What are the recommendations, having it welded or look for another frame?

[Jules]

Hi Morris, I'm no expert in this field but in the second pic, it looks like it may have been weld repaired before?? anyway, there was an earlier thread raised about the effect of springing those tubes, but that ended up cracking under the engine. There was lots of discussion there about how to weld the tube then (and spacing the plates)....

[RichardL]

Morris, sorry to see this. I would say, "weld by a professional." Here's the link to my cracked-frame thread. A long read about how I cracked my frame trying to spread it to fit the front engine mounts. Then, pics of the welded repair.

https://www.a7a10.net/forum/index.php?topic=15945.0

Ricjard L.

[RDfella]

Don't just weld the crack, it won't last. Remove the tin shroud and follow the directions I posted a while back (sorry, no idea how to re-visit the post) which involves inserting a tube inside to bridge the fracture and then brazing the joint and the inner tube.

[Swarfcut]

Morris. I'd suggest a repair. Another frame could be just as bad, and I have experienced body filler masquerading as a brazed joint! This was on a similar S/A Frame. Here we cut away the tube top and bottom and did a repair along RD's suggestion. This allowed internal support of both joints.

   This similar repair is somewhat awkward and in a highly stressed area. A simple butt weld joining the tube walls is unlikely to be strong enough, and as RD notes some sort of additional support to the join will be required. The expertise is out there, there are various options to complete the job, and bike frames have been fracturing like this and successfully repaired. So while annoying, the end of the world ain't now.

 The cause is down to stress on the frame parts, with  engine vibration a fatigue fracture results. Additional spacers will be required to ensure the engine, mounts and frame all line up with little or no stress. Stating the obvious here, but it is tempting to flex everything to fit rather than spend time making spacers. With an unknown frame, never trust that the mountings and lugs are as they should be, let alone the quality assurance "fits where it touches" of the 1960's West Midlands.

 Swarfy.

 

[RDfella]

Just located the pics I attached when describing my A10 frame repair. Seems to be in a similar place, too.

Edit:
Here's what I did:
1. cut away tin shroud on side affected for access
2. drill 10mm hole through frame (just vis in pics) around 3/4" each side of crack
3. cut crack right through & chamfer faces
4. spring frame ends apart for access
5. with flapwheel or similar clean up inside of frame tubes for a distance of at least 2"
6. turn up a tube to slide inside frame tubes, approx same thickness as frame tubes
7. mark centre of insert with felt tip
8. put insert in one side of tubes, re-align frame tube ends
9. slide insert (those 10mm holes are handy) until it's central inside the join.
10. braze insert to frame tubes through 10mm holes
11. finally braze join in frame.
The purpose of those 10mm (or thereabouts) holes is twofold - they help in moving the insert across the join but, importantly, they allow the insert to be solidly joined inside the frame, ensuring a strong joint.

[morris]

in the second pic, it looks like it may have been weld repaired before??

Well spotted! I hadn’t noticed because I assumed that the weld was from the wrap around plate…
Following the suggestions made I think I am going to have it brazed RDfella’s way. Thanks for digging up the pictures.
Another frame means I will have to re-register the bike or have the frame number restamped which can develop into a bit of a minefield.
It’s a bit sad really because I finally got all the niggles ironed out of this bike and now this comes up.
Well… keeps boredom away I guess?
Thanks for the support lads!

[RichardL]

Morris,

Not arguing that the internal-tube splice isn't better, but, in your case, the old weld was not done by a professional (IMHO), so can't judge it against an internal splice. RD is about to tell me the fracture point is between the more brittle weld and the more ductile tube. Perhaps, but, as evidenced by these fractures, the tube is not all THAT ductile. According to my welder, it's important to choose the right rod for the TIG weld. Time will tell if I've introduced a new fracture potential, hopefully, learned by some future owner after I'm dead.

Richard L.

[Rex]

let alone the quality assurance "fits where it touches" of the 1960's West Midlands.
 Swarfy.

That's a little unfair Swarfy. I've always been impressed of the frame build quality of our bikes. Examples of the art of craftsmen compared to the contemporary Japanese efforts.
Not anti-japanese either, as I rode 'em to work for decades.

[bsa-bill]

my Rocket Gold Flash had both down tubes cut and a piece removed a solid rod inserted and re-welded; I think the reason would have been to alter the handling it certainly turns quicker than the Flash.
Not being sure who had done the welding I took it to our local engineering firm and had it redone, point is I think if you're going to weld it the insertion of a suitably sized rod with a bit of tube removed may look odd but will allow the tube to be welded to the rod rather than to itself (does that make sense)

[BagONails]

Weld or braze there are pros and cons to both.  Welding uses highly concentrated heat to fuse a localised area and additional filler alloy is introduced to reinforce the area, the advantages are strength and possibly the only solution if access is limited and you cannot displace the original tubes either side of the crack sufficient to get another tube inside to reinforce the joint. Preparation is everything and the crack or split must be 'v'd out to ensure full penetration. Tig welding would be preferred. If only a crack and you can see both ends, drill small holes through the tube at the limits of the crack to prevent further crack propagation before welding.  The downside of welding is that it can introduce additional localised stresses and distortion due to the high heat, melting and resolidification of the parent material.

A brazed or silver soldered repair is generally more forgiving and gentler on already aged and fatigued /corroding tubes. The temperatures are much lower and the heat is spread over a much larger area. The heating is slower on the way up and slower to cool which helps to relieve stresses. It is not as strong as welding over the same cross sectional area but if you can insert a fluxed reinforcing tube the braze will flow all around the joint wherever the surfaces are in contact by capilliary action and you will end up with an immensely strong and tough repair that will potentially cause less stressing to the existing frame.

My choice given the option would be to reinforce and braze if at all possible as per RDfellas' reply

[BSA_54A10]

Morris,

Not arguing that the internal-tube splice isn't better, but, in your case, the old weld was not done by a professional (IMHO), so can't judge it against an internal splice. RD is about to tell me the fracture point is between the more brittle weld and the more ductile tube. Perhaps, but, as evidenced by these fractures, the tube is not all THAT ductile. According to my welder, it's important to choose the right rod for the TIG weld. Time will tell if I've introduced a new fracture potential, hopefully, learned by some future owner after I'm dead.

Richard L.

Richard,
The old weld was done by a 2nd class process welder at best
But most likely by Rosie the Riveter repurposed because we were no longer at war.

[morris]

Bit the bullet and had it welded.
A mate who's a professional welder was extremely confident that his TIG weld would be as good as anything else so we had a go at it.
Time will tell if we made the right decision.
Now some dents to work out and then off to the painters...

[bsa-bill]

Fairly neat job

[BigJim]

Great background on that last photo. How did you get on Morris, would be interesting to hear if that weld has held together for some miles?