This is a valve spring compressor adapter I made for installing valves on a Kawasaki FD501V in a John Deere LX188. This has a valve spring cap with an OD of 0.865" and I've used an ID of 0.700". This makes it really easy to install valve spring retainers.

Obviously, this one may not fit your application, but you can scale it in the X/Y axis as needed. 

As always, PETG is ideal for functional prints, but PLA or anything else will work fine. Modeled in inches, so if it shows up tiny, scale up by 2540 to convert from mm to inches (Mainly an issue in Cura).