Whenever an engine sits idle for some time, at least one set of valves, sometimes more, will be open to the atmosphere. Air, and moisture cycles in and out of the cylinder due to temperature changes. It's not uncommon to find one cylinder heavily rusted, to the point the piston meets a big obstruction, while others show little or no damage. I remember a very low mileage Oldsmobile 350 with rust pits so deep in one cylinder it had to be bored and sleeved, even though it was possible to re-ring all the other cylinders to standard bore size. That one cylinder had been open to the atmosphere through an exhaust port, while the others had remained sealed up. It only sat unused for about six months!
Jerry
