Hi, by the direction this 4 pronged 'nut' works I think that the 'slotted' round bit in the centre unscrews with a RH thread.
make or find yourself a 'two lip' large screwdriver or possibly adapt a 1/4" screwdriver socket from your socket set.
+ apply some heat to free it up I guess.....
succes

Hi Vincent

Thanks for the suggestion, I will give it a try

email (option): steve@bsa-inc.com

I'm not having much luck with removal of the 'slotted' round bit in the centre as it is very difficult to get a purchase on it as the two slots are very shallow.

Has anyone got any ideas of the best way to proceed or does anyone know of any JAP engine gurus and which forums they frequent so I can get a bit more advice/suggestions?

Any help appreciated

email (option): steve@bsa-inc.com

Problem solved.

Tig welded an old socket in two places to the 'slotted' round bit in the centre. The heat from the Tig welding and use of a ratchet drive easily allowed removal the offending centre part. Incidentally it was a LH thread.

The outer 4 pronged drive is an integral part of the gear sitting behind it in the picture

email (option): steve@bsa-inc.com