Mizkaki

Joe,

The needlebar movement is usually measured at the bushing just where the bar enters and exits the head. The best way is with a gauge until experience allows you to eyeball it.
Many Singers (ie 401, 500 and others of that era) and sometimes other brands have two timing marks (score lines) on the needlebar. On these you lower the needlebar to it’s lowest point (DBC) the upper timing mark will just be at the bottom of the bushing. Then raise the needlebar until the lower timing mark is in the position that the upper mark was at before moving. This movement was .093”.

You said that the machine is stitching with its new needle. Leave it, after all this is your goal. The .093” measurement is an old industry standard. The factory and techs in the field learn that you sometimes have to fudge this due to casting and machining variances.
Use the .093” as a starting point.

The Japanese 15 machines with the bobbincasse/ hook facing the left usually have the timing pin set. If this has been changed it is very evident. The pin will have been punched or drilled out and the hole threaded for the set screw and usually another hole will be drilled and tapped for the second set screw.. So unless there is a set screw or two at the timing point, I doubt that the timing has changed. It probably has always been just barely off of the standard .093”.
Hope I helped.
Cathy