cylinder head

[jiminicricket]

hi all can anyone give me an idea as to why my c15 has blown some lumps out of the combustion chamber as shown as the dark patchs in the photo it has only done 1k since rebuild regards.  Jiminicricket

[snowbeard]

not that I could answer your question, but maybe with a better picture? 

[BSA_54A10]

If there is no corrosponding damage to the top of the piston then it was probably some earlier cracks or corrosion that let go under operating conditions.
Polish it smooth and shove it back on.

[jiminicricket]

thanks to those who answered there was no damage to the piston so may just do that (polish it up and bang it back on)

[beezalex]

I'm sorry, but it's still not exactly clear what you're referring to in the picture.  I see some pitting between the valves directly across from the spark plug that looks like the result of detonation or corrosion (hard to tell) and I see carbon deposits (pitch black) around the perimeter of the exhaust valve and near the spark plug.  The former is in a very unusual place for detonation damage and the latter is because you're running too rich.  Is there much carbon on the piston?  What compression pistons are your running?