Carbon in water passages?
 

We had to tear down my friend's 540 due to a faulty rocker arm. The engine has maybe 15 hours on it, broken in properly on a stand,and then ran hard.

With the head gasket off, the water passages around the cylinders are black, and leave black trace on my fingers that smells like carbon. On one part where the gasket partially extends over the deck from the water passage, theres a big black circle that looks just like the carbon on the top of the pistons. IMO it is carbon, but I can't understand how this much gets into the cooling system.

What can cause this? Head gaskets not sealing? When the engine was running, it ran nice and cool. It tends to get a little hot when it starts for the first time in the water, but we figured air bubbles in the sea strainer/system. Once it cools down, it ran at the 180 degrees of the thermostat all day long.

Only a slight tap made us tear it down (to find the loose rocker arms).

Thanks for the help

Joe

Look for a crack in the cylinder wall.

Ouch, I hope not! Will check