Hi everyone, I have a 74 350 with low miles that I disassembled and attempting to rebuild. I know some times its better to just take it to a machine shop. If I have to bore it than so be it, I plan to measure clearances tomorrow. If all checks out will these black marks be a problem?

 

If you are not boring it, you should hone the cylinders. A good hone will probably clean those up. What caused them?

 

Believe it or not this is after flex honing. From what I've read its rust that occurs in a low oxygen environment. Has anyone ran in to this?

 

This is my opinion having rebuilt many engines...You will never have proper oil control, you will lose compression and have excessive blow by... period. You will need an over bore to do it correctly.
The hone marks are not right either. They are too horizontal.
A good house has a good foundation...same goes for an engine.