My son was riding my '05 Beta Rev 3 and he said it just died when he was going slow after an hour long ride in the hills, then the kick start was totally frozen. I initially thought he scorched the piston but it seems fine. Then I thought the kick starter gear might be jammed but that's not it either. No shimmer in the oil and it had plenty of coolant so I don't think it overheated. The + wire connection to the fan was a bit loose so it might have not been running but I assume it would have caused a seized piston if that was the culprit. I can move the piston without the jug installed by hand turning the rear wheel with it in 5th but it's pretty tough and I feel like it should move freely without anything causing compression.  That makes me suspect the crankshaft bearings or something in the gearbox but I don't know any other tests besides splitting the case. Also still can't make the kick starter move after removing the jug. Anyone have any experience with these symptoms? Thanks 

Couldn't you remove the clutch basket and disconnect the the primary gear from the rest of the gearbox.
Then you can check each of the crank and gearbox individually.

 Pull the mag cover off and turn the flywheel backwards with a socket and ratchet. If it`s mains it will probably free up. Happened to me during an event and pushed it back to the pits, spun it loose made it back to section 3 and it stuck again. Pushed it almost 5 miles that day!

 Of course you have to do new mains, seals and gaskets.

On 7/6/2022 at 5:47 PM, lineaway said:

 Pull the mag cover off and turn the flywheel backwards with a socket and ratchet. If it`s mains it will probably free up. Happened to me during an event and pushed it back to the pits, spun it loose made it back to section 3 and it stuck again. Pushed it almost 5 miles that day!

 Of course you have to do new mains, seals and gaskets.

You were right. I put the jug back on, pulled the mag cover off and spun it in reverse. Sure enough the kickstarter freed up and it fired right up. Definitely sounds like the bearing is toast. Thanks for your input.