Cleaning up corroded ali castings (+ welding/repair)

[cardiffrob]

I have this new race head for an old sidevalve and, as you can see, the water inlet has 80 years of accumulated grot in it. What would anyone suggest is the best method of cleaning it back to good material for welding up (TIG) without removing more than necessary. Ideally someone would know the name of a 'wonder chemical' that eats corrosion but leaves good metal (Yeah, right!)

Failing that, sandblast the living daylights out of it with glass beads???

Failing THAT, make it new with 2mm sheet?

Any suggestions would be welcomed.

Thanks

Rob, near Cardiff.

 

[Shox Dr]

Caustic soda (careful) and bead blasting.
Then cut back to good material, and weld on a new piece of tube

 

[brightspark]

sandblast it. bead blastings no good as its not abrasive enough to cut the crap back. ok for light corosion though as it piens the surface

 

[Shox Dr]

Sorry should have picked up on that. You need to be aware of what you are blasting it with, for a start it really needs to be new, or at the very least known to have only been used on clean Ali. Otherwise the process will force all sorts of crap just where you'll be welding

 

[cardiffrob]

Good point. Thanks.

Obviously silica sand is a no-no so what grit is ideal?

 

[Shox Dr]

Garnet

 

[hotrodder]

Personally i prefer to use a die grinder with a burr after i've hacked off the properly rotten bits. With that amount of corrosion it's like grinding chalk until you reach something that's more ally than oxide. Bead blasting is what i'd use to finish up the repair if/when an invisible job is important

Whichever route you take to prep it the trick IMO is to not try to weld a fresh bit of ally tube directly to what's left of the origional. Strike an arc and (assuming it doesn't stutter and immediately 'blow out') gently build the amps and see what happens. Almost certainly crud, spitting and arc wander with no recognisable weld pool. Tickle it with the die grinder and go again, after a couple of rounds you should get enough of a weldpool to add some wire (4043 or 4047). 'Butter' the joint with a couple of passes and then you'll have something niceish to weld to

 

[Shox Dr]

As ever Pete, you fill all the important bits in that I do but forget to mention.

 

[hotrodder]

Or i'm giving away too many trade 'secrets'

That thermostat elbow looks nearly as bad as some cast ally water cooled boat exhausts i repaired a while back. Only 30 odd years old but had spent pretty much every day of that under water. Brackish water. Boy were they not fun, i came very close to throwing them in the bin and telling the owner they dissolved in the cleaning bath

 

[brightspark]

[cut back the absolute rotten bits but sandblast the rest.that takes u back to good metal without cutting any decent metal away with a die grinder