I have been checking the oil stick, adding oil from a quart bottle down a funnel to add oil as needed. The problem being it is hard to judge how much oil I have added and it could result in excess oil.
Today I filled a 4 ounce jar then added it down the funnel. It needed more after the addition and I added another four fluid ounces which brought me close to the full line. Put the funnel and jar on a cloth to let them drain and left them on a shelf for next time I add oil. The funnel and jar are upside down on the cloth and will not collect dust. With this method you cannot overfill.
By overfilling an engine too much the oil can start foaming from being splashed all around by the crank. As it is, the oil is typically only high enough that the crank can pick up enough oil to splash it up into the cylinder. But if too much oil is being splashed by the crank, then it is about the same effect as putting too much soap in the laundry washer, it foams up way too much, and once the oil foams, it keeps foaming, and eventually almost all of it ends up being foamed up and then has pretty much ZERO lubricating abilities anymore. Slightly overfilled will do nothing really, but being meticulous like mentioned above can't hurt. But especially an older machine, little overfilled won't hurt cuz it'll prolly burn it off soon enough. But if you get more than about a quarter inch past the MAX line, you very well could be (but not guaranteed) asking for problems down the road.
No prob. The question actually reminded me of a joke I played when I was Teacher Aide in Small motors class in high school. A student came to me and asked a question. He had a pretty good understanding of things during lectures and whatnot, seemed like he mostly knew what he was doing, so I figured he was being a smart @$$ when he asked the question, so I gave him a smart @$$ answer...
The question was "what do I do if the oil is just touching the bottom of the dipstick?" I answered (again figuring he was joking with me) "Hold the dipstick upside down till the oil runs up to the FULL or MAX line, then fire up the motor."
So yeah, he actually did just that, the motor blew up after running for a while, he told the teacher, I got yelled at (although the teacher did see it as kinda funny afterwards.) So I learned not to assume anything when students ask what I think is a stupid question. It then got to the point of getting the look like, I can't believe you gave a serious answer, I was screwing with you...but that was better than the earlier alternative.