Could do with an explanation of just about all the parameters but maxMotorForce is the one that just makes no sense.

Say you have a jack, car lift, ram or anything similar.
So
rigidBodyA = ram/piston
rigidBodyB = base
generic6Dof.setLinearLimit(new Vector3D(0, -4000, 0), new Vector3D(0, 0, 0));
generic6Dof.setAngularLimit(new Vector3D(0, 0, 0), new Vector3D(0, 0, 0));
generic6Dof.getTranslationalLimitMotor().enableMotorY = true;

You want the ram to be able to lift a certain mass.
so
Moving in Y only with default gravity
to lift a rigibody of mass 200 the maxMotorForce seems to have to be 33.333 or greater.
Where does that value come from?
What actually is maxmotorforce in terms of mass and force?

Instead of using maxmotorforce If apply a centralforce of 2000+ (mass*gravity) to rigidbodyA then everything works fine.
And it will stop within the bounds of the constraint (as long as the force is less than the all the mass in the system).

just dont get maxmotorforce :(