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Is this Bad? 1971 CB750 K1


CB750 Member
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Minnetonka Minnesota

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?

No not yet, I don't have this bike in my immediate possession I was just taking some pictures and I noticed this. I was wondering if anyone has seen anything like this. I can see the spark plug in there which to mee doesn't seem like a good sign
Seeing the spark plug isn't an issue, if you look on the other side you will see it also. It looks like the cast for the head was bad, not the head, and you have extra aluminum on the fins. I would take out the plug just to make sure the hole isn't compromised. I would not take it all apart without looking that over and maybe a compression check first.