The very top part - the small centre part I have cut off - was. The rest is smooth down to the end of the crank and there is a small lip part way down. Too small to get a slide puller to grip it. Nothing was screwed into the thread as this was for the puller to be threaded into it to remove it. The remaining smooth bore, and the fact that it slightly widens at the lip about 15mm in, is why I was thinking of threading it and putting a long bolt through it to push against the crank. I would get the same effect if I welded a nut to the end of remaining coil. Probing inside it I can feel where the Woodruff key is and if I turn it on its side and fill the hole with plusgas it leaked out at various points where it joins the crank. I can say with 100% certainty that it is a push fit with a Woodruff key to stop it spinning. I haven't attempted to pop it off for a while but I am now tempted just to get it off anyhow - with the exception of damaging the crankcase as this has the engine number on it.

I can only suggest threading it and using a high tensile hex head bolt as the jacking screw, put it under tension and soak with plus gas, tap the head of the bolt with hammer, heat the bolt head and le the heat transfer through to the tapered surfaces, more tension.

Repeat until successful

Hi I am from Mexico , Torreon Coahuila and have just one YA 6 of 73 newly bought yesterday . I know we will have some language barriers , but I would like you to comment a little more about how it works with start up . I do not see my electric motor .
I still can not get turned on, I have spark , gasoline in the carburetor and apparently will not start .
A greeting and thanks for uploading your project .

Hola yo soy de México, Torreón Coahuila y tengo justo una YA 6 del 73 que recién compré ayer. Se que tendremos algunas barreras de idioma, pero me gustaría que me comentaras un poco mas de como es que funciona el arranque con marcha. Yo no veo ningún motor eléctrico a mi YA 6.
Yo aun no logro encenderla, tengo chispa, gasolina en el carburador y al parecer no quiere arrancar.
Un saludo y gracias por subir fotos de tu proyecto.