Magnetos always have safety break screws fitted to them to prevent that kind of damage,one for a single and two for a twin4, Remove spark plugs
replace them into the plug caps and 'earth' them out somewhere on the bike while turning the motor over Magnetos dont like producing a whole heap of voltage (spark) without somewhere for it to go, ie the spark they produce if not discharged somewhere outside the mag, the earthed plugs in this case, will possibly find a way to earth inside the Magneto damaging it.
It's simple to do just wrap a bit of wire around the thread and maybe a pushrod tube etc.
if you're doing this with petrol leaking etc make sure it doesn't ignite is etc!
HiThis is one long oil change!Not sure where the gearbox drain plug is located.Lools like it could be the large brass nut on the lower front corner of the gearbox/kickdtart cover,next to the.exhaust pipe.One of the books states it's behind the kickstart cover.Any help appreciated.Dan
Danno, in view of the number of questions you have raised on the forum surely the time has come when you need an experienced Vincent owner to visit you and give you some guidance. There's plenty of them in Hertfordshire. Anyway, the gearbox drain plug is hidden from view but still readily accessible behind the big alloy plate on which the kickstart cover is mounted.HiThis is one long oil change!Not sure where the gearbox drain plug is located.Lools like it could be the large brass nut on the lower front corner of the gearbox/kickdtart cover,next to the.exhaust pipe.One of the books states it's behind the kickstart cover.Any help appreciated.Dan