Let's start with the removal of the crankshaft and transmission – simply because I already had a gutted engine block lying around.
How to clear out the right side of the engine beforehand is described in the thread "Timing chain replacement NX250" viewtopic.php?t=694. The timing chain often starts rattling after 50,000 km and should then be replaced at that time.
hopefully the crankshaft is ok viewtopic.php?t=2379
After removing all the engine casing screws, lay the casing on its left side and loosen and remove the right side with light taps of a rubber mallet. Often the casing half doesn't come loose immediately; in that case, heat, penetrating oil and patience will help. Do not hit too hard, the brittle cast aluminum can break.
In this engine, the timing chain was apparently loose and wore down the teeth on the crankshaft; as a consequence, the piston was destroyed by contact with the valves. Remnants of it can still be seen in the lower right of the engine casing.
First, the gearshift is removed. To do this, slide the claw to the left and remove the shift shaft. If only the gearshift's return spring is defective, the transmission and crankshaft do not need to be removed. However, if the engine has high mileage or if there are metal shavings in it, it is better to disassemble and clean everything and to at least replace the ball bearings of the crankshaft and the balance shaft.
You can buy OEM parts directly from webike in Japan; at least for Europe, it's fast and inexpensive (see parts for NX250 engine overhaul thread viewtopic.php?t=2419)
gearshift reset spring 24624-MT3-000 https://www.webike.de/products/24338121.html
gearshift return spring 24651-KF0-013 https://www.webike.de/products/24338128.html
