The following was put into the for sales section of the website by a friend of my father's. It may get a better responce here...


I am searching for advice as we in WA are having problems with welding some later model A7 aluminium crank cases. If one attempts to weld these crank cases (tig) the aluminium becomes so stressed it cracks again with severe conviction. So much so that one cannot overcome the ever on going cracking no matter what one does. We have tried to weld them cold, stich weld. and then preheat the case over night to about 200C. All the attempts are in vain!!

If any one has some magical answer hidden up their sleeve I would be most grateful for any advice that would resolve our dilemma.

Regards and thanks in anticipation,

Doug Baker
Scarborough
Western Australia

I had the N/s front engine mounting welded on my Chummy (63712) over 30 years ago, it was just about ready to drop off. The welder was a coded welder for the ‘Ministry of Defence’ (submarines). He did say that the case was porous and oil would keep on seeping out so had to be cleaned over and over. It was preheated to a specific temperature and did not distort at all.

Hi,

I have used 'Lumiweld' on a non-stressed part of a crankcase, we heated up the crankcase first on a gas bar-b-que to get it up to a temperature that was too hot to hold. As long as the crack is opened up and the surface cleaned as much as possible you should be able to bond 'Lumiweld' onto it. They reckon that 'Lumiweld' is stronger than the original aluminium but I am sure that is only if you get a good bond.

Initially it struck me that it could be "hot shortness" - a phenomenon that affects welded aluminium and creates never ending cracks in the cooling weld pool. Usually recified, if my memory serves me right, by a change in the filler rod composition. The welding supplies people should be able to help with a better filler (probably with more silicon).
It's over 20 years since I studied the welding of aluminium alloys for my thesis so my memory is being hard worked on this one!

The other option might be thermal cracking - but the 200C preheat suggests that isn't the issue.


Charles

The works crankcase of the TT car was badly damaged when I bought it,no2 rod had broken in the past and broken the cam centre bearing housing.This had been repaired in the past but the distorted cam had not been straighted.Subsiquent running of the engine rebroke the bearing housing and there was a multitude of cracks over the block face. No amount of welding could repair this so the only solution was as follows.
The crankcase was sand cast and the closest relative is a mag crankcase.So the centre bearing and a section 2 inches long and 3 inches deep was cut from a donor case.The same section was cut from the works case.The old mag centre housing was built up with weld in prep for line boring.The works case was left in a degreasing bath for 2 months. The the donor section was welded into the TT case.All went well but the case distorted and the top face was approx 1/16 ininch abovethe centre .This was machined flat and the cam housing line bored for the larger dia centre bearing.A plate under the block and its been running fine for a year to date ,on the road and in competition up to 6500RPM ,a credit to all those craftsmen involved.The weld on the side of the crankcase are hidden by the supercharger.

Hi all. As I have some days ago replied to a similar request from our West on our club website, I won't repeat it all here. The best help to a good weld is as much the proper cooling down (to gradually relieve the stresses) as much as the heating up & welding. The only thing to add is, because I haven't done any for some time, the amount of silicone (if any) in the rods used, which I will check with a friend who has been successful for almost 50 years. See website www.austin7club.org (you can click onto it here from this Links page)for a long rigmarole. Cheers, Bill

As an addendum to above : I've checked with my learned friend & he advises that although silicone content helps the flow of the welds somewhat, pure aluminium rods are best on either sand-cast or diecast crankcases. Cheers, Bill in Oz

Sorry, but I keep getting extra thoughts on omissions with above. (Does that make me an Oxymoron?). I've assumed you've used aluminium welding flux in your Oxy welding. Mix the flux into a thin paste with metholated spirits, coat on rods, burn into rods with oxy torch before starting weld. When the job is cold, wash vigorously with warm to hot detergent/water, then scrub with wire brush. If you've used too much flux you'll probably have to repeat. Although we're talking crankcases here, on sheet metal it's also vital you clean off flux completely, otherwise likely to gradually eat it's way through filler &/or paint maybe 5 years later. Cheers, Bill in Oz

Just an extra note - only ever use a stainless steel wire brush, and file rather than grind. To do otherwise contaminates the weld surface with iron and/or carbon causing inclusions in the aluminium weld. Generally the best welding rod is the parent metal - steal a sliver from a web.

If it is any comfort, I have been unable to successfully weld shock links - horrible alloy!

Cheers,
DG
(also from down under)

Hello Dennis,

Thanks for the advice perhaps you might like to contact me off line.

Regards

Doug Baker

To Ruairidh and all the list,

A sincere thanks for the effort and the time you have taken to offer your advice. I am truly amazed with the sincere generosity of your replies and input to resolve this problem. As a footnote it is my intent to have the material analysed so I have better understanding of what the animal is that I am dealing with. When I have the results of this deduction I will inform you all. Till then thanks once again.

May your Austin give you trouble free motoring

Sincere regards

Doug Baker