I recently bought a second hand BMC teammachine 2016(?). The frame looked in really good condition. Back home I started the build by servicing the headset. Af purchase time the stem was off the fork, and I did not ask why, I assumed because of transportation. I cleaned, tested the bearings and they felt very smooth, so I put it back together with new grease. At the step of ajusting the preload by tightening/loosening the top cap I could not get the right amount: or there was play, or it was too tight and rubbing (the headset cover would not turn with the fork, same for the spacers , unlike the stem which would turn). I first thought I had put the bearings the wrong way around, but I can rules this out now.
I dismantled my commuter road bike, which headset I have serviced successfully in the past, and noticed that the only difference is that it has a compression ring (metal ring with an opening) between the top bearing and the headset cover.
Is that what I am missing here? Is it possible for the BMC headset to come without the compression ring?
Here are some pictures of all pieces making the headset, as I've bought it. The compression plug is inside the steerer tube, it is fitting there snug if it matters. Also I have run my finger through the headset bearings cups on the frame and they feel very smooth to me.