Held the Belleville washer in some vice grips and slightly enlarged it with a cone drill to allow it to clear the threads. The hardened washer clears the keys on the motor shaft.
My original washer was cracked so I could never tighten it.
I removed the spark plug and filled the cylinder with a light cargo strap to lock the engine to help tighten assembly.
Hi Weka, I have probably a hundred of them here in a box but postage to NZ is cost prohibitive. Myson lives in Ukland so I know postage well. Glad you got it sorted