Hi! welcome to the forums!
Cool looking asset!
When the engine part is fully Kinematic its almost as if it has full control over anything it’s attached to.
Try increase the mass of the marker for the engine vibration and make sure it has Translate Motion = Soft
I did a tips and tricks for a heart beat which would act the same…
https://forums2.ragdolldynamics.com/t/heart-beat/187
Hope this helps
J