My singer 4166 sewing machine won't pick up the bobbin thread... I've changed the needle and cleaned the bobbin area rethreaded etc... I'm pretty sure it's the "timing"... Is this something I can fix or does it have to be serviced??

The bobbin may be in backwards
the needle is not the correct one for the machine
the needle isn't correctly seated in the needle clamp
the machine is a little bit out of time.
Remember to hang on to the needle thread when you're trying to pick up the bobbin thread
Turn the handwheel in the direction that would advance the fabric from the front to the back of the machine
make sure the bobbin-winding spindle has been pushed back to the left for sewing
make sure your needle is inserted correctly as far as it will go with the flat side facing back
and that the upper tension disks of your machine are threaded correctly.
Make sure the presser foot is up when seating the thread through the upper tension.
Turn the hand wheel (TOWARDS YOU ONLY) never turn the hand wheel away from you and hold the needle thread lightly. .
pull the loop up and then pull both threads (top and bobbin) under the foot and toward the back of the machine.
Also could be a timing problem

Customer Support ,,,,,,,

Clean the bobbin case area thoroughly, and probably the feed dogs, too. Start all seams by holding the top and bobbin thread ends together behind the presser foot for the first few stitches. If you have lost your manual, pick up a new one, free, at http://www.singerco.com

the tension at bobbin seems to be the problem, make sure bobbin thread is in placed in bobbin CORRECTLY...then it should not be loose but loose enough to pull out with the slightest pull, top tension should be set on around 4,,,,,

this link is for the manual it may give you some assistance with your problem
http://www.singerco.com/uploads/download/546_7463_efs.pdf

If the needle is slightly bent it won't pick up the lower thread all the time. Try using a new needle.

There could be several things causing this.
First, be sure the bobbin is in the bobbin case correctly. There is usually a line diagram showing the correct placement or you can check the owner's manual.
Second, make sure your needle is inserted correctly. If it is not completely set in the housing, this can prevent the bobbin thread from being caught by the hook. The groove in the needle should be ffacing toward you to assure that the thread interacts with the hook.
Third, be certain the upper threading is correct...passing through all thread guides and correctly through tension and take up lever.
Finally, make sure the bobbin case is free of lint. The machine brush that came with the machine will clean this area well.
I hope one of these suggestions helps you solve your problem. If so, please come back to Fixya and rate my advice!

The bobbin goes into the holder in what would appear to be the wrong direction ie, the thread doubles back. If this is correct, the bobbin tension might be too low, there is a screw on the bobbin holder to set the tension.

open the bobbin case and see if the hook is turning, if it is it is just a timing problem with the hook and needle, if it isn't tuning you may have a broken gear or timing belt.....It eill need to be looked at or adj by someone who repairs them....Daniel

indicates needle /hook timing is off check/ adjust or take it to a repair shop for adjustment
singer have a very good manual on how to set timing so download a pdf version from the singer site