Hello, I am working on my grandpa's 1971 CB750 K1. He bought it in 1971 and used it until about 1985 when it sat in a garage on a dirt floor. Surprisingly, there is very little rust and the pistons aren't stuck. The kick starter turns over just fine. I haven't tried starting the engine yet but I noticed this on the right side of the engine at cylinder 4. Now I am not a professional at all, but to me, it seems like a casting issue from the factory, just because I don't see any corrosion. The motorcycle used to run just fine so I am curious as to what this is, or if it is a problem. As of right now, I do not have any more pictures or close-ups of this issue. Let me know what you think this is and feel free to drop a comment. Is the whole engine trashed, or is there still life for this old Honda?