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I've just received my engine and started checking parts, specifically the valve head. There are areas between the cooling fins which are blocked by excess metal as a result of the casting process. Some places there is a small hole which could be opened by some careful filing. Some places there is no hole but the area could be opened up by drilling a small hole then filing carefully. My question, is there any danger in doing this other than the obvious careless mistake of breaking through a critical wall?

I couldn't upload a picture here but if you go to my website, there are pictures in the ENGINE menu.
(http://Www.expercraft.com/cdgundy) or just search "Light Earth Aviation".
Oops! It seems Expercraft has changed something. Just try the search of Light Earth Aviation.

You should do this if you expect the engine to cool properly. I used an angle grinder with a thin cutoff disk to open up the fins. I then drilled to open the holes in the passages through the heads. Be very careful not to drill into the ports.