Unfortunately this is not a simple "yes/no" question.
Sometimes an engine can be disassembled and there is little if any cylinder wear, especially if the oil has been changed regularly and the engine has been properly cared for. If there is no wear you can hone the cylinder walls and put new rings in, provided that the pistons are also not worn. Obviously worn pistons need to be replaced as well.
If the cylinders have as little as a couple thousands of "taper" you need to have the cylinders bored and replace the pistons/rings with an over-sized version. That kind of cylinder "boring" doesn't change the displacement enough to make any significant difference.
Enlarging the cylinder bore will increase cc's in a 2 stroke and ci's ina 4 stroke.....
Not without some insanely big bore sleeves.
The bore refers to the Inside diameter of the cylinder. The Piston will be nearly the same diameter, with the piston rings making up the difference. Convert the bore to area by multiplying by pi and dividing by four, and multiply by the stroke and the number of cylinders and you have the volume displacement of the engine.
Possibly worn cylinder bore(s), or worn out or broken piston rings.
Changing the cyl bore does not affect the ignition timing of the engine.
what determines when should bore and engine
No. There isn't enough material in a 305 to bore that far oversize without hitting water.
Worn cylinder bore, worn piston rings, poor valve seat condition, tired valve springs.
The Bore of an engine is the tube that the piston goes up and down in.
Yes. Boring the cylinders means that you have made the hole bigger. Although it's only a few thousandths of an inch difference, that is quite a lot when the piston is traveling through there HOPEFULLY for a long time. If you bore the cylinder without putting in the appropriate sized pistons & rings you will have NO compression and the engine won't run, and even if it did, it would wear out VERY quickly. So, YES, you do need to put in new pistons and rings when you bore the cylinders. And while you're at it, if you live in a high altitude (4,000 ft elevation or above) you can usually select pistons that will raise your compression by 1 point without causing trouble for the computer.
std bore is 4.050
You bore and stroke any piston internal combustion engine the same way. You replace the crankshaft with one with a longer stroke, or have the stock crank machined to increase its stroke. You also have to bore the cylinders to whatever size you want, within the limits of the cylinders, and use shorter connecting rods and larger pistons that match the diameter of the bore. Then you reassemble with the proper size main bearings and piston rings, and you have an engine with larger displacement.