How do you set the timing for a Singer hd110 ?

I bought a Singer HD110 in February 2007. This is the 3rd time that the timing if off. Could you tell me how to set the timing myself? Also, I have a 29-4 Singer industrial patching machine, that I cannot keep the tension right. I have the manual for it, but it's no help.
I have replaced a bobbin shuttle body and the tension disc and spring. It runs for a few days, then completely goes out of whack. Can you help me? Thank you

Vickie Felos
July 2008