Guru
Joined: 11/02/2018
Location: AustraliaPosts: 1910
| Posted: 10:01pm 26 Jan 2023 |
"How can I avoid it? So running the tank empty is a bad idea? Better to shut it of by the switch?
This is just speculation.
1) As it was running out of fuel there would have been a lot of extra oxygen in the exhaust producing oxides of nitrogen.
2) When the engine stopped the exhaust valve was open.
3) As the engine cooled the water vapour (note 1) in the exhaust condensed and reacted with the oxides of nitrogen producing droplets of acid that, with the remaining oxygen rusted the valve stem.
4) When you tried to start the engine the rust prevented the valve stem sliding back through the valve guide.
5) No compression, no start.
Note 1
When a hydrocarbon burns in oxygen the carbon produces CO2 and the hydrogen produces H2O vapour.