Lower looper needle broke

Question

machine was working great when the lower looper broke,i was informed that it was because the timing was out, my friend who is a mechanic has been for thirty years knows he can replace the looper, he thinks the reason it broke was because the s***w was loose and had nothing to do with the timing,as it had been working great, please help with a solution, is it possible for a person with a great deal of mechanical knowledge to do a home repair, thank you