I bought a 1994 cbr 600 f2 last week. Someone tried working on it and the thermostat houseing was missing. I sprayed some water in while cleaning of the bike. Well when I went to change the oil, water poured out of the drain plug. I pulled the motor and checked it out. I cant see a hole or crack. Wondering if it might be a head gasket? The oil cooler and cylinder walls seem fine.

 

Are you sure there wasn't water in the oil already? I'm assuming that if the thermostat housing was missing that you didn't run it -- so if water transferred from the cooling side to the oil side by the pressure of only a waterhose I'd say you got big problems with that motor. Since you already pulled the motor, I'd go ahead and do a complete tear down on the head and definitely a new gasket. Still, I'm wondering if there's any other way you can think of that the water could've mixed with the oil -- doesn't seem likely that it just migrated over simply by spraying it. Was anything else not on the motor while you were cleaning it?

 

Well before I pulled the motor I ranwater into the thermostat houseing useing a funnel and about 3/4 of a gallon went in before it started pouring out of the oil drain plug. I checked the oil cooler and houseing, nothing. I checked the water jackets of the cylinders no cracks or holes. I looked at the head but there are alot of small passages I couldnt get a good look in. The only bike salvage place in the area said they had an f3 motor for $325 but he also said it has a blown head gasket.
Cylinders 2 and 4 seem to have residue looks like burnt coolant maybe?

 

Doubt this'll help ...

I changed the stator cover gasket once. Rinsed out the housing with waterhose (to get rid of gasket material that I scraped off). Pulled the oil drain plug and water came out. Maybe he did the same. I left the drain plug off for about 2 hours so that any water would evaporate then filled changed the filter and added oil. Bike's been fine ever since.