SB 9 Back Gear will not stay engaged

[RVbeemer]

Lordbeezer, my #84029 has the same adjuster screw & locknut as your photos.
matthewmuppet, I think the lathe in question is the solid headstock non-removable spindle bearing & cap model. It’s The super finished type, like mine.
rvbeemer, i think the detent you are missing (between the backgear lever & the spring) just keeps tension on backgear fore and aft movement. Maybe just enough tension to keep it from popping out of gear. My lever does not appear to have detent notches in it, so I guess it’s tension only, just restricting loose movement. You can make a detent.
And remember, I’m by no means an expert. I’ve had mine almost 40 yrs, I know most things about it, but still no expert.
It appears your detent may have shot out under spring pressure when removing the backgear. Kind of like parts flying out of a pistol (never to be found) during dissasembly.
rvbeemer, your SB9 looks really good in black.
that’s all I got.
and I could be wrong about any of this.

Mac, It may be for restricting loose movement but may be enough pressure to hold it. Doesn't take much.
I knew there was a reason for the hole with a spring in it. You may be right about the ball shooting out but I'm guessing whoever "rebuilt" this lathe, probably lost it and went on with assembly

 

[lordbeezer]

Mine has a plug instead of ball. Little more bearing surface. Can measure if would help.

 

[RVbeemer]

Greetings All,
An update on my back gear problem. I removed the lever and installed a ball, I actually had one on hand, reinstalled. No luck. The shaft has more slack than the ball will take up. So, I removed the lever once more after marking the hole location, and ground a slot across the side with a rotary file until the pin would fit. I actually found a 1/4" pin with a detent ball on hand! Those good old junk drawers! So, everything fits good, the lever will not ease off, problem solved! I am going to cut the pin shorter today. Thanks to everyone for suggestions and ideas and trying to help me.

 

[DavidR8]

Greetings All,
An update on my back gear problem. I removed the lever and installed a ball, I actually had one on hand, reinstalled. No luck. The shaft has more slack than the ball will take up. So, I removed the lever once more after marking the hole location, and ground a slot across the side with a rotary file until the pin would fit. I actually found a 1/4" pin with a detent ball on hand! Those good old junk drawers! So, everything fits good, the lever will not ease off, problem solved! I am going to cut the pin shorter today. Thanks to everyone for suggestions and ideas and trying to help me.

Very happy you got this sorted out!