OK First things first, I am a total novice at welding. I have just bought a SIP migmate 105 Turbo jobby. I have never welded anything in my life. Now I have recently sent my Ali/Alloy motorcycle cylinder head to various places and upon re assembling it I noticed that somebody has been kind enough to drop it and looks like give it a little kick about too. Anyway there is a small crack on the outside that doesnt go through, infact its a visible crack but not penetrated. I just want to seal it back up just in case it wants to get any bigger. I have 0.8 Ali wire, 1mm oversized tips, and some pure argon gas. How do I go about completing this task. The metal itself is about 5-6mm thick, with the crack being about an inch long, but I dont want to go through it. I have had a go but i dont get much actually sticking to the metal head, I get a lot of black sooty residue, and lots of blobs dropping off my tip. Some advise on wire speed and aps would be helpful too. Many thanks guys.