The cylinders of my IO-540-C4D5D have a green stripe painted on their cylinder head. According to https://www.lycoming.com/content/understanding-engine-color-codes, this means that I have 0.010 oversized steel cylinders. There is also a side note, where it says: “Color code applicable only to engines overhauled in the field. Lycoming does not sell oversize cylinders”.
What exactly is oversized about my cylinders, and why would oversizing be part of an overhaul and what is a possible side effect?
The cylinder bores were machined slightly oversize to remove wear and fitted with new matching pistons. Before new replacement PMA cylinders became widely available (driving down prices) it was standard practice to overhaul cylinders when the rest of the engine was overhauled. There is no particular side effect and if you have a good shop to do the cylinder work it may still be cost effective. On some engines cylinders may crack due to thermal cycles when they have a lot of hours on them, regardless of having being overhauled or not, but I don’t think your IO-540 is terribly prone to cracking cylinders.
Interesting. Thank you. This means that my cylinders have more volume, hence suck in more air/fuel, hence should generate slightly more power at the same RPM.
A tiny bit, yes 
About 1 HP
