Folks, another appeal to the experts on the forum.
As you can see from the picture, some past hooligan has been a little hasty with the spanners, or perhaps he leant his bike against a tree stump... Anyhow I have to contend with a few broken fins.
As luck would have it, the one on the block is the third fin from the top...
Has anyone any advice to offer on how I should tackle this? Welding technique, rods, pre-heating etc. I'm reasonably confident with the MIG on steel but I have never done any aluminum welding, so while I'm happy to have a go (i have a spare Bantam head to practice on) I'd also be happy for someone to do it for me...
TIG is easy. Use a 5% silicon rod and glass bead blast the metal to remove oxides. I would preheat it, but some don't do much preheating unless you are in the middle of a big mass of metal. Nev
Hi Simon, as Nev says, TIG is easy (if everything is right). Pretty much everything else is hard work.
If you haven't got a TIG, you could try Oxy with flux filler rods. Your MIG welding head will probably be too big to get in there? - but you could use it to tack the edges.
Without LOTS of experience, only an AC Tig will work.
With Aluminium, everything needs to be super clean. Even oil that has got in the casting pores will cause you problems. You'll need a new stainless steel wire brush and a fancy solvent - or at least alcohol. Pre make the fin with a higher silicon aluminium, and maybe drill the hole a little larger.
You may not be able to weld right back into the break, so if you can round off the broken fin and make a close fitting repair piece, it won't be obvious. I have done this on my Mk2 head and it looks ok. 2-3cm of weld on each side.
I would V the edges back a little way to get as much new metal in as possible.
You will have to grind the weld back to get a spanner to the head nut.
Practice on something less valuable than the Bantam head. You might find it's going to need some practice time spent to get it right, and welding cast is sometimes harder.
If you can get a heap of sheet offcuts it would be good. Maybe 1.6 to 2mm
The major issue with Aluminium is that it always has an oxide coating and the oxide has a much higher melting point than the parent metal. If the weld pool looks crappy or you are having to push the filler rod under the pool, give up, grind, clean, and start again.
Also, be wary of the whole lot collapsing. Don't hang around too long with the heat.
It's worth learning how to weld Ally - but it might also be easier to pay someone? I did a night course at TAFE to get started.
Good luck, brenton
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.
