The steering tube was machined for 41mm bearings, but the bearings I had were pressed into cups for another bike and I could not source them again... I ended up cutting apart an old alum frame to make some adapters, 41mm>34mm, 34mm is the standart headset diameter for mtb's.
I rode some more today, all went perfect and the bad noises are now gone. There is still an unpleasnat sound at mid RPM while accelerating, I think it comes from the motor :/ I'm tempted to raise the power up to 2,5kw but I fear the motor will not like that. Rigth now the bike is fast but lack some neck breaking acceleration and hill climbing power. It sures climbs, but slow (20kph
) Still, it is so small and agile! That makes me more confident in keeping speed in tigth areas where I was usualy slowing down a lot, now I can keep accelerating and change direction in a hearbeat.
On a less positive note, I think the rear swingarm is bent, the rear wheel is not in line (vertically) with the frame and front wheel :/ I don't know if this happend while riding but I dont like that at all. I will probably need to make a new swingarm and jacshaft soon