3D print ideas

Helmet hooks on wall, washing covers, exhaust plugs(tpu), hooks, radiator sand protection grid(tpu), watch/computer handlebar mounts could be usefull. Makerworld and other 3d sites have print files and settings. 

Best ones I've seen are 3D printed oil funnels with threads.

Great for 2 strokes or certain bikes where the oil fill is awkward to get too. Saves any drips or spills.

The thread doesn't need to be too amazing, just good enough for a secure hold

Little “spacers” to take the free play out of KTM/Husky throttles.

Printed oil funnels are great. It's the first thing I'd print...

Friend of mine printed a replacement clip for my chest protector after i crash tested the original. Works fine.

Whatever you print for use with bike maintenance, make sure your filament is chemically compatible with whatever chemical it is going to come in contact with. 

A chain gauge, a chain greaser (you can find them already designed online). I watched a youtube video of a guy 3d printing a gasket for the bowl in his carb. I'm not sure how well it holds up to gasoline but it was pretty clever regardless. I like tool holders/organizers for all of my moto specific tools in my tool box.  You can print some multiboard which are free files and make all kinds of random tool holders. https://www.multiboard.io/ 

I built an electric bike with a CRF450 frame and 3d printed all of the mounting brackets as mock ups before I cut any steel. I didn't need the radiators so I printed shroud brackets in place of the radiators. I made a DC switch holder that goes inside the stock tank so it looks like a gas cap but its actually the switch.

 I designed and made a tube/tool container for my gravel bicycle, I'm sure you could make something similar for parts if you do woods riding. 

This is very important to consider.

PETG is going to be your best bet for most things that contact chemicals of any kind, or will be exposed to UV light.  PLA is by far the most common material and easiest to print with, but it will degrade quickly in the sun and does not tolerate heat well.  A word of warning for PETG though, make sure you have the right bed surface on the printer because it likes to weld itself to anything it touches, I use a smooth PEI sheet on my printer that I can be pretty rough with to get the parts off.

OP feel free to PM me if you have any material questions, more than happy to help.