My Whyte 901 circa 2012 developed a knock in the front end from the headset. I have removed the stem and forks and both cartridge bearings from the tapered headset, I was planning on ordering a new set of cartridge bearings to replace this set however am unsure what to order. The headset is the stock FSA orbit ZS (I presume this means zero stack), I am now thoroughly confused between integrated, aheadset, internal headset ect can anyone tell what sort I am running and if this impacts on what cartridge bearings I can use. Thanks in advance.

Note: I did take it to my LBS who confirmed it was the headset but declined to sort it out because “those monster MTB headsets are a pain”, so I think he must just have a roadie bias, hence having a go myself.

You sure the headset didn’t just need tightening up? Bearings wearing causes it to be gritty to turn, not knocking.

Same as a road headset though, your LBS is crap! You get taper steerers on road bikes too. Did they check it was tight?

give this a try:
https://www.canecreek.com/headset-fit-finder

No they didn’t check it was tight, but I have tightened it up myself and still had a small amount of play. I have the 1.5inch bearing out now and it is certainly rough and gritty feeling, it seems to have plastic shield rather than rubber seal, so I don’t think I can try re-greasing it. Thanks for the link above will have a look.