And if sombody can tell me why my exoust got so hot...

its usually caused by lack of water flow through the exhaust, did it just happen on one side or both ?

The amount of water was good new exoust and impeler

did you back flush the system ? you could have blockage in the coolers

I would try and get a small bore a scope (camara) and try to look in the cylinders.

But i had a good amount of water coming aut of the exoust

That is a good idea...maybe if i can find it somwere

You will probably see why it got so hot when you pull the head off to replace the piston. My bet is that the piston is melted and the head gasket blown between cylinders

Piston melted i bet...

Post a pic of the plug number. Obviously there are deeper issues, but it does look like a longer reach plug than what the heads take.
So kind of curious.