First of all, there is no tension adjustment for the walking foot. Walking foot is a generic term used to describe alternating presser feet. This means the foot itself is in two parts each with its own separate shaft. When one part of the foot is down the other part of the foot is up, and vice versa. This is just a feature to aid the machine in helping heavier thicknesses of fabric to go through the machine easier.
The needle can't hit the bobbin itself, it could hit the hook, but not the bobbin or the bobbin case.
Timing the machine means adjusting the machine so that the hook passes by the needle at just the right time to go into the scarf of the needle and pick up the bobbin thread.
There are a couple things you should try before you do anything else. Change the needle, making sure the needle is all the way up into the needle bar as far as it can go, and snug down the set screw that holds the needle in place. Make sure the grooved side of the needle is pointing to the left, and the scarf is pointing to the right. The scarf is the hollowed out section of the needle just above the eye of the needle.
Make sure the bobbin is installed correctly. The thread should come off the bobbin to the left and then be brought under the bobbin tension after pulling the thread through the groove in the front of the bobbin case.
Try that first, and if that doesn't help, you need to take the machine to an industrial sewing machine mechanic and have them set the tensions, the timing, and check for worn or broken parts. You should really do that anyway, no matter what. I strongly urge you not to try to make any adjustments on your own.
Here is a link to the instruction manual and service manual for the Pfaff 1245. While this is not an exact match to your 145, it is very close. http://www.pfaff-industrial.com/pfaf...sults#ergebnis