I had a craftsman large rider mower with a v-twin engine that kept bending pushrods. I would remove the valve cover, straigten the rod with a hammer, pound on the end of the valve to unstick it, and slap it back together to finish the yard. I did that about 20 times.
Then I saw a youtube video that said that is caused by overheating and a mouse may have built a nest in the shroud around the air cooled cylinder. I took the shroud off and, yep. That cylinder was completely caked in dry mud and straw. I had to chizel it out of the fins with a slot screwdriver. And the other side had a nest too, but it was all feathers and straw - no mud.
It ran great after that.
Now you got me thinking. We also have a Murray Select rider w/a 46” deck. Put a good bit of money into it - two tires and rims, new blades, new headlight lenses, new battery, plugs, seat cover, the whole Magilla. Ran great for a quarter acre, then stopped cold. The starter motor cranks independently, the engine turns freely, and I replaced the starter relay. Still nothing. I even hotwired the seat safety override. I have a new ignition switch and throttle relay to install, but now I wonder if one of those little pests maybe got in the garage and chewed on some wiring I can’t see. I mean, there’s only so many parts you can replace on the thing that could cause it to stop like that.