07 kx250f knocking

[bigbike]

The other day, my sons bike overheated. There was blue smoke and a burnt odor. From looking at the plug, it was running very lean. I relaced the rings and the main jet but there was a knock in the motor and still running lean.
I check further and found some play in the connecting rod big end and the left crancksaft bearing. I put in a hotrod crank assembly and oem cranckshaft bearings. I still found a bit of play in the left bearing even if it fit thight on the crank and in the crankcase. After re-assembling, I still have the same knocking and still runs lean. I double checked timing chain and everything. I starts and runs good. I tried another crankshaft bearing and it still has some play. Is this normal? If so, what would be the knocking noise?
THANKS!

[deuceshigh7]

well the rod should have left to right play, but up and down play is bad.. don't know which motion u are referring to but what happened to mine was that the bearing housing cracked and was allowing the rod and bearing to slide around...

if u are running lean, take apart the carb and do an overhaul on it with some carb cleaner and compressed air, there might be something stuck in one of ur jets...
-nic

[Dave16]

It's probably your cams they are probably too close to the valve buckets.

[steviep]

if your valves are shimmed incorrectly it could be a valve hitting your psiton and if you dont get it checked asap u will have a big problem on ur hands so make sure u get the valve clearances checked and make sure everything in the head is good bc these kawis have said to have very bad head probs...i also have experienced this me and my friend have gone through 4 heads bc of valve buckets shattering