Thanks both for your replies.
I’m rebuilding the engine and treating it to a new crank (new old stock bought for a great price a couple of years ago), new bearings, seal, clutch refurb and a 12v powerdynamo/vape kit.
I’m going to try locally heating the crankshaft around the key and see if I can remove it without damage. If not, I’ll do the obvious and source a new one…….
I’ve stripped the engine and it’s the only part that hasn’t come out easily……..although I’ve yet to press out the bearings. Been pretty impressed by how easy these engines are to work on. I bought a clutch removing tool for the clutch basket but have made do with my collection of drifts and 2/3 legged pullers (made by me during my apprenticeship….a long time ago!) from my toolkit for everything else.
Probably needs a rebore but that can wait to things free up after this bloody virus passes!