07 250f lower rod bearing failure?

The other day I was riding on my motocross track and coming out of a corner while I was getting back on the throttle my bike just lost all power and bogged down so I hit the kill switch. When i tried to kick the motor it was super hard to kick so I hauled it back to the shop took the valve cover off timing was ok, cam chain was ok, and valve clearance was in spec. I turned the motor over by hand it seemed ok so i tried kicking it again and it kicked fine until it finally fired, which it took forever to do and it usually starts on the 2nd kick, it bogged and died and was hard to kick again. I have both side cases off the motor and everything seems to be fine so far. I just rebuilt the whole motor probably 20 hours ago and did not replace the crank because everything was inspect according to the manual. What do you guys think?

Start with the simple things first. Eliminate the carb, air filter, spark etc. etc, etc. Although none of those would explain the hard to kick over. If you do get to the point that you are tearing down the engine, inspect as you go down. Inspect the cams, cam caps and cam bearings. Check the piston and cylinder wall.

Kind of strange that it was hard to kick then you were able to turn it over by hand. Maybe check out the auto decompression and double check the tensioner. When you say you rebuilt the entire motor except the crank does that mean you still split the cases and replaced bottom end bearings/seals and what not or did a top end?

I split the cases replaced bearings seals and what not. When it was hard to kick it turned hard by hand for a while and then eventually felt like normal again after a couple rotations of the fly wheel. Somethings binding somewhere. And whatever it is caused my motor to bog down and loose power but it didn't make any weird noises when it happened. I've already been through the carb checked spark

Since you split the cases I would double check the flywheel and make sure it hasn't backed out or worked its way loose and that it is still lined up on the key correctly. That would explain why it is sometimes hard to turn over. Could be the chain binding up a little. Might explain why it is hard to start & bog down but didn't actually jump a tooth. Also makes sense that it got easier until it fired again. When kicking it doesn't nearly comes close to the rpm as running so it could have "un-binded" itself but as soon as the motor fired up it binded up again. I have also seen bolts back out on the clutch side (idler gear, balancer, etc" and give enough play to not mesh up and cause binding. Doesn't really explain the loss of power but could be something to check. Once its hard to kick try spinning the wheel backward to see if it frees up. Hope that helps.

how many metal shavings in the oil filter?

My big end just seized on my 07. I stripped it all down and the rod was solid then I got the crank out and it ended up freeing itself but when I rotate the rod on the crank I can feel its locks sometimes on the rotation, so yours might be doing the same , the bearing is breaking down so it's locking then unlocking.

My big end just seized on my 07. I stripped it all down and the rod was solid then I got the crank out and it ended up freeing itself but when I rotate the rod on the crank I can feel its locks sometimes on the rotation, so yours might be doing the same , the bearing is breaking down so it's locking then unlocking.

yeah that was the problem, exact same thing that mine was doing

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