Crank hard to turn

Dont know if this has been posted or not but need help

I bought an 08 yz450 SE. The guy told me it had the top end done right before he got it. It would crank right up first or second kick when cold but then when it got hot it would kill and wouldn't crank up till cool again. It seemed like something was putting it in a bind I don't know, I have rode alot of dirtbike that were race ready but not a 450 and it has been the hardest to kick yet. So I it took had the valves adjusted and did whatever and the mechanic said it started right up first kick rode it a little ways and it died said it sounded like it locked up made a loud sound. So he Crunk it up again and he said it killed back out said it seemed like something was dragging so he took the clutch cover and clutch off and I went and looked at it because I didn't understand what he was talking about. I got there and you can barely turn the crank with the cylinder and head on and without the spark plug in and he don't know what it could be said he never anything like it.

Remember it ran great till it got hot before he messed with it. Any help would be great

Could the timing chain tensioner be to tight? Idk alot about dirt bike motor have only tore into a hand full of them and took a stab at it

You need to isolate the parts or part that is stuck/sticking. If the engine is fully assembled minus the spark plug it could be almost anything. I'd start by checking the cam chain tensioner. I've seen people actually crank them down instead of simply releasing them. After that remove the cams and check them for scoring, also inspect the journals. If it's still tight you can remove the clutch and primary drive gear to determine if it's crank/ top-end related or a transmission problem. Good luck. Btw, sounds like you need to fire your mechanic.

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