I am guessing your Mother's mower had a Kohler Courage single cylinder engine.
Those engines have been very troublesome. It seems like everytime they get one part straightened out, another part gives trouble.
-Some of the early engines were shipped with the top cover not torqued properly, and the block cracked near the exhaust valve cam gear.
-They probably had a good design in the counter-balance weight, but it slid back and forth in a similar fashion to the design Briggs and Stratton was using and Kohler changed it when Briggs complained.
-Then they went through a spell where the rod would seize to the crank and break. Kohler repaired several at our shop that were just plain questionable whether it was a manufacturing problem or negligence on the part of the owner.
These engines are particularly sensitive to being low on oil, so if you ever have one, check the oil every time you use it.
There was one that the crank seized in the bottom main bearing. Kohler said they thought some had been made with the main bore undersize.
There were several issues with the re-designed counterweights, On some the bushings the counterweight moved on loosened up in the counterweight. On others with aluminum bearings on each side of the counterweight, the aluminum bearing shattered.
One thing I would like to stress here-The Courage twin cylinder engines seem to be every bit as good as the Kohler Command engines. Its just the single cylinders that have so many problems.
As far as older Deere mowers go, They are pretty good mechanically. The hoods are a joke and expensive to repair. I cannot say much about the box store Deeres, I would stay away from them if they had that same Kohler engine in them. Most of the better Deere tractors run Kawasaki engines. They are pretty good, although some of the older water cooled Kawasakis do have a camshaft that may prove to be a problem after 600 hrs. or so.