It's not a washer! It's a seal protector that goes above the boss.
If it is loose on the crankshaft, throw it away.
These alloy protectors were introduced to prevent grass wrapping around the
crankshaft and destroying the seal, thus preventing the scavenging of the fuel mix.
In rural areas, it wasn't grass that chewed out the bottom seals on Victas. It was bits of hay band left lying around [often also used for tying up garden plants to stakes, on farms]! The worst cases resulted in the seal spinning in its seat, and chewing out the seat. When this occurred, we'd glue a new seal in with epoxy resin, and warn the owner to clean up hay band from their lawn.
If they did not, it was going to be a full stripdown and bottom half crankcase replacement for their mower, if it happened again.
