Below you can see the half part of the right (as we ride the bike) of the crankcase. Be aware that the driveshaft and the countershaft are actually alligned so the 2nd drive gear and the 2nd Driven gear are in contact. In the picture this is not happening because when I split the crankcase , countershaft moved so in picture is a bit higher from its original position.
I will try and explain a bit how the transmition between Neutral and 2nd works:
2nd Drive gear rotates as it is attached and "locked" to the countershaft.But the 2nd Driven gear is actually rotating freely on drive shaft (Neutral Position).It needs 4th driven gear to rise up,bind with it and force drive shaft to rotate (2nd Gear Position). This happens because the 4th driven gear is bind to drive shaft in a way that they rotate together but the gear can move up-down.
4th driven gear is moving up and down because the 1st fork embraces it and forces it to move like this.The fork its self is forced by the gear shifting cam rotation. The fork has an cylinder arm that it is attached to the cam's guidlines.Guidelines look like this
(sorry for diagram but i have no clear picture for it)
As the cam is rotating it forces the arm (and so the fork ) to move up or down to certain positions. The arrows on the pictures indicate the position of 1st and 2nd shifting fork as cam rotates to 1st, Neutral and snd gear.
When I eventually opened the crankcase I believed that the damage would be something obvious.Possible broken teeth of gears, forks, or other parts.The real problem was that everything looked ok (with no excesive damage but all parts had minor surface - contact - damage). I made a conclusion that all this small problems were added together and formed the automatic gear shifting problem.
What is happening:
As 2nd driven gear and 4th driven gear come close, the damaged contact surfaces cannot hold the torque provided so the gears detach (To see exactly how these gears work please consult a online part store or wait for me to post a picture!).The detachment pushes the 4th gear down so the fork is forced to move also.Eventually the fork's arm presses the cam guidline and the cam rotates to neutral.
If you look carefully on the picture you will see that the 2nd gear position is in a guidline that forms "a top of a hill" on that spot.So it is easy for the arm to rollback to neutral position.
I hope you can understand what is happening.Plz forgive my expression mistakes but mechanical terminology in english is something completely new to me.