I have a relatively old Craftsman 34cc 4-stroke string trimmer that broke all the teeth off the recoil gear. I modeled this to be similar to the original, using the original spring and string. Roughly 70mm x 70mm x 36mm in size. This will insert and be held in place using the original internal tooth lock washer. 

The middle disc is a tad flimsier than the original but has held together. Some reshaping may be necessary, as I am still working on this model to finalize. Having said that, it has worked for 2 weeks. 

I would not recommend PLA. I did not have ABS or Nylon around, or else I would have chosen one of those. I printed the model in PETG, Temp 238 °C, bed temp 80°C, and 55% infill. I will probably print again at 75% infill. I ended up having bed issues and printed the model on its side. When working with the model, I could only get tree support to work in the areas of the model that needed support.