Weird engine banging sound

[jabba.rides]

I have a 86 kx125 that I got at the beginning of the summer and have not had much time to work on it yet, but am excited to ride it soon. I have done a few thing like clean the carb replace the clutch discs and replace the spark plug. However I recently noticed that the engine makes this weird banging sound. I have a few other issues like the fact that the top end leaks coolant that I recently noticed. However I want to know if this sound is normal and if not what it could be. Any help would be appreciated as I am rather new to this bike and bike maintenance in general.
https://drive.google.com/file/d/0B1Y7U4BU9d14V19FT1ZHaWVGeWs/view?usp=drivesdk

Thanks, Jabba

[KXDINO]

DO NOT start engine , pull top end off and inspect , coolant in the combustion chamber is a major disaster waiting to happen.and needs to be fixed.

[Rocco H.]

Hello. I had the same problem with coolant leaking into the cylinder, took the cylinder head off and put a very thin coat of gasket maker on the cylinder and cylinder head. That stopped the problem.

[umberto]

Coolant leaking indicates a warped head. If you put it on a flat surface, such as a pane of glass, you should be able to see the warpage. I think there may be a guide on here on how to lap your head, I'll try to find it. As for the knock, that sounds bad. I would pull my cylinder off and check your rod clearances. You've most likely got some wear issues and may need to rebuild the bottom end.

[umberto]

Here is a handy guide on how to check rod tolerances if you've never done it before.

http://www.kxriders.com/forums/index.php/board,56.0.html

[jabba.rides]

I took off the cylinder head and put it on a mill at my work and checked the flatness with a dial indicator it seemed to be fine. I've replaced the gasket and it is no longer leaking. I did not see any coolant in the cylinder when I first took it apart. It is still making that weird noise. I wonder if there is something wrong with the kips?

[Rocco H.]

Did you check clearance's on rod bearing's and that stuff?

[Foxx4Beaver]

doesn't sound like this does it?

https://www.youtube.com/watch?v=2XjmsMtcbL8