must look when I am home, but it's one of the last in Book 2, where you put the second big part with the two stanchions similar to the one on the back on the chassis...
and it's just the wrong sense... so if you pull the ones in the back out, the ones in front go back towards the chassis... so... somewhere must be a mistake or chainwheel turns in the wrong direction...?!
I have no idea...and I would be grateful for every idea that could help me get back in the game :)