Lately our generator has been using oil at an increasing rate. A little over a week ago after I had added oil . . . about 10 seconds after I started the generator I heard what sounded like "pffft". I looked over by the oil dipstick and found that it was gone! After turning off the engine I found it a few feet away, cleaned it off, put it back and started the engine again. When I restarted the engine again I was a little too close leaning over to see what would happen. Yep, it went flying out again along with a mist of oil on my white shirt. I've since rigged a wire clasp to hold the dipstick in place so that we can at least keep running the generator and check the oil level every several hours. The pressure in the crankcase is caused by "blow-by", which happens when the piston rings begin to wear out letting some of the combustion gasses get into the crankcase. Oil also gets into the combustion chamber and some is also pushed past the crankcase gasket.
I showed what was happening to the generator repairman. Even though he had been told what I had seen he still startled and jumped when the dipstick blew past him. I had to chuckle a bit.
I took a couple of videos showing the dipstick getting blown out. One video that I took only shows a loud "pffft" sound and a puff of mist because the dipstick was in tight to begin with. I lightly pushed in the dipstick so it wasn't in all the way and took the following video where you can see the dipstick more gently pop out.