did you "pre-flight" that engine before you started working it? Oil level, airways clean, no leaks, air cleaner, etc....any idea of when the last time the crankcase oil/filter had been changed?
And surely would help the engine experts here if you could provide the full engine make/model/type info from the engine's ID plate....

One would always like to see more than 80 #s , but you don't always. Sometimes , how fast it builds compression can tell you something. The engine has a compression release, so that compression # itself isn't a tell all. For me, I would check oil level and see if it seemed contaminated w/ oil or seems normal. The correct oil level is obtained by wiping down the dipstick and setting it at the low point on the tube w/o screwing it back on. Is there fuel present in the filter that you can see? Try a new spark plug?

Thank you both for your responses. It's good news to me that it may be something other than a big engine repair.

Regarding questions- the mower has a 16 HP Kohler. I will look for the id plate for any more information. I was told that the mower went to the local John Deere dealer every year for maintenance.

I've checked the oil every two hours before this happened and it's always been full and looked brand new. I'll check that again using the technique suggested. I don't know if the mechanic did a "pre-flight" as I wasn't home when he was here. I'll check those things and try a new spark plug if everything looks good.

Thanks again for the help.