I have done one through the sump in the past, fiddly but worth the effort to save an engine stripdown. However, before going in, all guns blazing, bear in mind I have had a few cb550 bikes where the kickstarter wasn't working - apparently, as in it failed to engage the engine when operated, often after an overhaul. Really odd as during the engine overhaul I would be using it a lot to check all the gears mesh etc etc, only to find it not engaging when trying to start the completed bike. Oddly the fault self cured after a shake down run - had it happen a few times either just after a rebuild or on bikes ( well engines) that have been stood for some time, though often they will have workedc fine for a few dozen operations, then start playing up. Never seem to get it once a bike is in regular use.