Coolant coming out of my pipe after top end rebuild

[Handymen72]

I have a 2004 RM125. I just completed my first top end rebuild. Bike started up after about 10 kicks. Ran for about 1 min. Shut off and noticed coolant coming out of my tail pipe. Bike also got a muffling sound. What did I do wrong?

 

[Rich Rohrich]

The cylinder head or cylinder base are leaking coolant into the engine. It's gotta come back apart to fix it.