Fork oil replacement for the second time

[3alfa3]

68.000km, second fork oil replacement today. First replacement was at 40.000km, today after aditional 28.000km. Only left leg like before.

I used Motorex 4W both times (16cSt@40C - original oil is 15,3cSt so the same).

When i replaced oil first time at 40.000km, oil was dark grey/black, lots of silver at the end of pouring into measurement jug. That time, it was obvious that old oil is bad, big difference when riding cold and hot bike.Viscosity difference was noticeable cold/hot.

Motorex 4W have Viscosity index of over 250 and from 40.000km to 68.000km did not noticed any difference all that time, both cold and hot.
That oil was almost the same color as new Motorex 4W i put today and with no or very little silver color at the end of pouring.

I used this method both times:

Both first and now second change, 395ml was poured out and the same amount poured in.

Oil and dust seals are old as bike and in great condition and i did not replace them.

[3alfa3]

Btw, some numbers...........   Stock 2020 Z900, EU model.....

I weigh 96kg (212 lbs) naked.
When i bought Z900 in 2020 (new), i put 5-6 aditional turns of preload for the rear shock so 7-8 threads are visible (forgot the number, but lets say 7-8 visible threads). Did not have to adjust rebound for shock - it was OK and its OK even today. Static sag is 10-12mm for the shock, rider sag is 44mm.

Forks:  preload is at stock settings: i have 36mm rider sag (20mm static sag). Rebound is 2 clicks left from fully closed. Its strange that stock preload give only 36mm since I weigh 96 kg naked, but its checked multiple times. Never had bottoming out, lowest zip tie position was 25mm from casting (15mm before casting is bottom for forks travel on Z900) so for the last 68.000km i had 10mm "to spare" and thats OK.

[JerryZ]

so there is only oil in one fork  ?!  whats in the other  ??  just air ????

[KellyL]

Originally Posted by JerryZ

so there is only oil in one fork  ?!  whats in the other  ??  just air ????

It's got some oil too, but just for lubrication. There's no damping involved in that leg.