My son has an 06 ttr 90.  Has been well cared for and runs great after a new carb rejetting. Was riding this weekend in the desert and my son laid the bike over in some soft sand on the left side -opposite the kick starter side.  Since his leg was trapped-it laid over until it stalled and until i could get to him-Possibly a minute or two.  So i picked up the bike, hit the starter and sounded lke a dead battery, so tried to kick it and would not kicK either- great- siezed motor. Pushed it back to the truck, pulled the plug and it was soaked with oil.  Kicked it wIth the plug out and a large amount of oil shot from the plug hole.  Good- not seized.  So i pulled the exhaust pipe and kicked it a bunch more Times to pump the oil out, cleaned the plug ( did not have a spare) put the plug in and kicked it.  Started right up but oviously lots of smoke and Oil mist that pertty quickly cleaned up.  Put the exhaust header back on and let it idle for 5 min.  All seemed well and we rode for probably 50 miles almost wide open.  Dodged the bullet.  Ran a bit rough on the top end i figure because of the oil soaked plug.  Next day-he drops the bike again on the same side (left) and same deal-cant turn it over.  Is oil somehow leaking up the timing chain race?  Seems it is happening very fast.  What else could it be? The bike runs so well that the valves dont seem an issue.  And it does not burn oil or smoke.  Any thought would be apperciated before i start tearing it apart.

My sons's TTR90 did the exact same thing last time we went riding.  I thought I was going to have to do a top end on it, but the smoke cleared up and it has been running fine since.

I don't know why it does it either.

Here's a guess as to what happened.  The newer bikes have crankcase ventilation that is directed into the airbox / intake to burn the fumes from the crankcase.  This is for pollution control.  There's a tube somewhere on the top of the crankcase that connects to the airbox.  Similar to your car.  Normally, with the bike positioned upright, or while riding, only crankcase fumes enter the tube.  However, when you lay the bike over, liquid oil can get in the tube, get sucked into the intake, then into the engine.

thanks punkinhead-that sounds logical, and the bike does have said vent hose, however if this were the case, i would expect to see alot of oil in the airbox and carb with all the oil that ended up in the cylinder-and there is none....still scratching

None in the airbox?  This is a mystery.

Punkinhead- i think you are on to something.  The second time he dumped it over-i did not drain the cylinder and run the bike-so i just pulled the air box cover and there is oil in there.  Looks like i need to route the crankcase vent hose to a high spot without a feed back to the engine intake- i know this is not the last time it will happen-son is still learning.  Good call.

Good detective work and persistence.  It sounds like the first time you just lost the evidence because you ran the bike.