How to....

[Flog]

Found the sprocket nut (is that what it's called?? - yeh I'm newbie!) loose today - how the chuff do you tighten it, as sunk in so can't get wrench on it? And.... why would it come loose or just life....?

 

[GrahamPaul]

That's a bummer. It's something which mostly seems to have afflicted Trek so far.

Bosch CX gen 4 chainring nut

Chainring nut / spider nut or other names... Has anyone experienced their chainring nut coming loose? Today is the first day my Rail has let me down, I had to cut my ride short today when I felt a vibration at my feet, checked the chainring and it was wobbling and the spider nut had come...

www.emtbforums.com

I started a thread on how to change the chain ring here: Bosch Gen 4 - How to change the chainring? - EMTB Forums

From this you can see the tools you need to remove the crank (a Park Tool CCP-44 is one option) and then a Spider Nut tool. I bought the Unior 8 Tooth Cartridge Bottom Bracket Tool - 1671.2/4

Watch out: many sales websites try to sell you the Gen 3 tools as being suitable for the Gen 4 motor. According to Bosch, they are different.

Also, the spider nut is reverse threaded. You do it up counterclockwise, should you decide to do it with a hammer and chisel...

The tightening torque is quite low (probably because the nut is aluminium) so locktite or similar is well worth it.

 

[Flog]

Reading the original post is pretty identical. Felt a rubbing / abrasion every turn and then looked down to see the chain ring going round like Del Boys robin reliant, squiffy. Although, not just the chain ring nut, while I was down there, also checked the pedal crank nut and that was loose as well.
Guaranteed if I buy the tools will be a one time use, may try bike shop and loctite.
THANK YOU