Alright dude, when does it knock, at idle, under load or on the overrun? That might give some indication as to what might be up with it.

If the shop said the big ends were good then dont worry too much, if the main bearings go then you'll get a rumble which will get louder and louder. Not a knock, well unless the ball bearings escape!

After 50 miles from a rebuild? Dont worry about the smoke at the moment really, might just be excess oil in the exhausts? It could of course be the right hand crank seal drawing gearbox oil in and burning it. IF the exhausts cross over like they do on the '16.

Could be worth going back to wherever rebuilt it, if your worried. They should be able to answer any questions!

Cheers
Paul
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More **** two strokes than you can shake a **** stick at.