Modern Vespa

Hi all, I had a full new Px 244 engine built 1690 miles ago with all uprated components and even new casings. I rode faultlessly until this morning, through the gears absolutely no indication of what was to come, pulling up hill in third/ change to 4, transmission dies, engine still running, but no drive. Turned off I can change gears on selector and clutch pulled in makes a difference like it's engaging, kick start acts like the clutch pulled in. There's no crunchy noises, and free wheels ok . Ideas please guys, I'm a bit rusty.

Clutch key ?

I would pull clutch cover and clutch and have a look. Anything else is a guessing game at this point.

Maybe the big circlip popped out of the groove in the clutch basket?

Whatever it is, it's clutch side related. Could be an eaten woodruff key or eaten primary teeth, especially if you used BGM cogs (lots of fails lately)…

Thanks Guys, interesting about the Bgm cog issue.

Put me down for "it's the clutch," too. In particular, I think you've sheared the woodruff key.

I sheared my woodruff key a few years ago and it was a similar experience. Assuming that's the case, you'll almost certainly need a clutch puller to get it off--the usual two screwdriver method won't work. Then there will be the question of if the crank or cog can be saved.

Crimaz make a hardened woodruff key for high output motors, but splined cranks are becoming a thing for a reason.

I don't think it's the cogs. Broken gear teeth tend to get caught up in the rest of the gearbox and jam it solid (at a minimum) in my experience.