Gravity not affecting bone


I’m trying to learn my way around the physics but I can’t understand why this isn’t working.
I’ve a skeletal mesh with two bodies (and thus two bones).
In the PhysicsAsset i’ve added a constraint connecting the two bodies at the shafts centre (see image attached). As I don’t want the upper body to move or rotate at all I have set it to Kinematic and disabled gravity. The lower body is being simulated, has a mass and gravity enabled.
However once I run the simulation, or add it to my scene nothing happens.
The constraint has the default settings but i checked the “Disbale Collision” box. Both bodies have a predefined mass and I disabled the “Collision Reponse”

I would expect that, using these settings, the lower body to rotate along the constraint and endup pointing downwards.

If I set the upper body back to ‘simulated’ both bodies detach (constraints doesnt keep m in place) and they start spinning and moving frantically.

Reimported, and regenerated the bodies. It works fine now.