Hi, my son got a 87 250 mojave that doesn't run. I found water on the piston and milky oil. I pulled the head and cyl off, and the head gasket is intact ( thin copper gasket) don't see any cracks in the head. The head was on tight. Anybody got any ideas?

 

Makes me wonder if someone took it for a swim. Lot's of stories on here about folks getting water in their engines while playing in the mud and water.

 

I wondered about that myself. Before I tore it down I had him drain the coolant(he said it looked like water), and fill it with antifreeze. When I tore it down it had some antifreeze in the cylinder. It gets cold here, I was concerned that it might have froze and cracked something, but I don't see any cracks in the head.

 

There is only a few ways water can get on top of a piston.
#1 Blown gasket, or crack.
#2 Ingested in the intake by air or fuel system.

Why wasn't it running? Personally I would have gotten it running first. Like tencubed said, it might have gone for a swim and there was nothing wrong with the engine.
Is an 87 Mojave 250 water cooled?
I would just put the thing back together and deal with it from there.

 

If there are no visible cracks you probably have a gasket leaking. To really check for cracks you need to take the water cooled parts to a machine shop that has the equipment to do this. There are a few different methods which any good shop will be able to do for you. Might have them check for warped gasket surfaces at the same time.

The fact that the anti freeze was in the cylinder indicates the problem was not as simple as someone submerging the bike.

 

the problem is most likely the meachanical water pump seal....i would flush everything out and replace that and you should be good to go.

 

Thanks for all the input, I'm going to pop the valves out to get a better look at the head while it's off, then check to make sure it's not warped. Will post results.