For health related reasons caused by way too much wildfire smoke, my F650 Dakar single was parked in a storage unit in Montana for just over two weeks. We took a trailer to retrieve the bikes. The F650 was a little hard to start and smelled flooded but did start, and ran fine. I rode it from the storage unit about 300 feet to where the trailer was parked for an easy level no-ramp loading. Almost to the trailer it coughed once, almost like a little backfire, with a slight clank. When I tried to restart it it wouldn't turn over. It acted like a weak battery which didn't surprise me at the time since I had to do a lot of cranking to get it to start the first time. We rolled it onto the trailer and hauled it home to Texas from Montana.
I put a charger on the battery overnight. Still clicking from the relay but no cranking. Suspecting a bad battery I used jumper cables attached to the battery in my Ford Explorer. Click click but no crank.
I removed and inspected and tested the starter. It was fine. I removed the spark plug so I wasn't fighting compression and tried to turn the engine by turning the rear wheel. It wouldn't turn. The wheel turns fine in neutral and if the clutch is pulled. Next I removed the countershaft sprocket cover and attempted to turn the countershaft using the appropriate 30mm socket and my longest 1/2" drive handle. In gear it won't turn more than to take up gear slack in either direction.
The engine is locked up tight in both directions.
When it died it had been running maybe one minute. It wasn't overheated or even revved much. I just was riding it towards and about 3 feet from the trailer at a speed and rpm suitable for riding it off the street and onto a level trailer.
I can offhand think of a few things that could break and prevent rotation in the normal direction - a valve head jammed between the piston and head for example - but am having trouble visualizing what might block it solidly in both directions.
I don't like this bike well enough to want to pull the engine for a teardown/rebuild, but if there is something that is known to cause such symptoms - failed pump gear or something - I would go in one side or the other for a look see.
Otherwise, I will have a carcass or boat anchor for sale or I'll part it out. But before I do that if anybody has had a similar failure, (or had a friend with one, or heard about one) with a good idea or two, I'm looking for wisdom.