trx250r has spark but wont start

in a car if theres antifreeze in the block the heads or black has crack and let water in but idk
 
that is what i think is a crack but i didnt see one and then i thought seals possibly but could it be the bottom end causing this if so ima buy a complete new engine or ima buy a big bore top end so id like to know what i can do
 
im not sure exatly where the water jets run on that motor so couldnt tell u
but some where either a gasket is bad or a crack
but it sounds like it could be a head gasket
 
no it needs to happen anyway it is bugging me and that seems easy to do and ill check that and i might tear apart the bottom end to make sure its all good and doesnt need a rebuild and how do i check if it needs rebuilt