Ive just tried to fit a Brand X 44IETS headset to my son’s Octane Zircus frame and it ain’t working.

Im sure Ive got the right headset. The head-tube internal diameter is 44mm top and bottom, and the cups pressed nicely enough into the frame. Popped the bearings into place, slid the split crown race onto the RS Revelation fork and offered it up to the frame.

No dice. Once it was in there, the fork wouldnt turn in the headtube. Its as if there are no bearings in there (I promise, there are bearings in there)

So I pulled it apart, knocked the bottom headset cup out and assembled it on the bench. Same again. Once its assembled, it wont go around in the lower headset cup.

Ive installed the odd headset in my time, but Im doing something very wrong here, or Ive ordered the wrong headset or something.

Any advice?

There are a couple of reviews, one Russian and one Spanish, under the link that you posted that may help. I pasted them into translate.google.com

Cheers Timba. The Spanish review says it all. Will see if I can find something to raise the bearings a few mm.

After mounting the headset not turn me the address, after unmount a couple of times, I realize that the bearings are not working because the conical portion of the fork is abutted on the inside diameter of the lower bowl, so had to reduce the diameter of a few millimeters to get it to work correctly bearing, ultimately if you’re a handyman and want to save a few euros, it is a somewhat drastic but feasible option.