After an afternoon of trying and measuring I replaced both the motors in my K-line S2. One engine was jammed and the other had huge play on the axle.
The swap is straightforward, apart from making more space with the multitool to fit my new motors (sanyo motors instead of the cheap Johnsson stuff) my hard time was to swap the pinion from the old to the new motors.
I used a small pully-remover (thing with a screw in the middle and 2 or 3 arms to fit behind the pinion) to get the pinions off.
The hole in the pinion is about 0.1mm smaller than the axle (3mm) so it doesn’t fit straight away. Hammering the pinion in place will destroy the axle of the new motor and the teeth of the pinion.
Here’s the trick; Heat the pinion with a hot air gun till it glows, pick it up with a small set of pliers and put it in front of the new motoraxle.
Put the motor in a wrench, so that the axle is straight and close the jaws. They will pu***he hot pinionwheel over the axle and after cooling down the pinion is crimped on the axle.
Thanks Daan for the hint. Will keep that in mind. Good job.