Singer 112w 115 timing adjustment for larger needle and stitch length changing help needed.

[DMH]

I need some helping locating information online on adjusting the hook timing on my double needle drop feed Singer 112w 115.  I'm moving to a larger needle (20) and need to know how to adjust the timing for these types of machines.   I have a needle bar that has no marks.  The instructions for this machine says it can still be done even without marks on the needle bar, but also says I should set the stitch length to 8. I'm not sure when I change the stitch length if it actually changes.  

I bought this machine from a couple on Facebook marketplace that has an upholstery business, but I have not had much luck with consistent operation since I purchased it a few months ago.  Everything from getting the right size table top from a swing machine supplier I would never use again to installing a simple knee lifter that turned out to be made horribly especially with this terribly made table top.

Edited Tuesday at 11:50 PM by DMH