My first top end rebuild and it runs like crap........video included

It's hard to say from a video, can't really separate the sounds and establish where the noise is coming from.

If there is a hard sound coming from the lower end then my guess is that the rod journal bearing is bad. Unfortunately, just about anything wrong in the lower end is a fairly major rebuild operation.

Another possibility is that you put the piston in backwards. Are you aware that there is a front/back to the piston? Did you get it in right?

I would recommend popping the cylinder back off and attempting a few checks on the bottom end. The connecting rod should have a small amount of play side to side, but no noticeable play up and down. If you can feel ANYTHING irregular in the rod as you rotate the crank or if there is any up/down play then the bearing is certainly toast. Even if you can't feel it the bearing can still be bad.

There are similar tests to check the main crank bearings. Pop the clutch and flywheel covers off, remove the clutch and flywheel and see if you get any movement of the crank in the bearings. With the flywheel and clutch off I would expect a little bit of motion in / out, but nothing noticeable side to side.

Rod

+1 good advise :)

maybe the main bearings are bad pull up and down on the crank/magneto see if it moves, +2 on the piston check lol