Hi mreese,
The option you are referring to (Build → Project Only → Clean Only “ProjectName”) is a Visual Studio option, not one that is exclusive to Unreal Engine 4. What actually happens when a Project Only Clean process is begun, is that Visual Studio not only cleans the Project, but it also checks to see if it is able to clean anything that the Project depends on. Since you are using a version of the Engine that is built from source code, Visual Studio includes that dependency in the Clean process, which ends up requiring a full build of the Engine. The same occurs if you attempt to rebuild the project only.
If you wish to be able to perform a clean at only the project level, you would need to navigate to where your project is located in a Windows Explorer window.
- In the root project folder, delete the Binaries, Build, DerivedDataCache, and Intermediate folders.
- Right-click on the project’s .uproject file and select the Generate Visual Studio project files option (this will recreate the Intermediate folder).
- Open the project solution in Visual Studio and Build the project (this will recreate the Binaries and Build folders).
- When the build completes in Visual Studio, double-click the project’s .uproject file to open it in the Editor (this will recreate the DerivedDataCache folder).
You should now have a “Clean” project without needing to rebuild the Engine.