318 motor valves

Hello everyone.
It turns out that I ask for the 318 motor valves that I am repairing and they tell me that they come in different measures +3, +5, +15, etc.
And stay in Chock, first see that I listen to that. Could someone help me where is that measure that refers to?
Thank you.

318 motor valves may have different measures that indicate the overmedy of the valve, that is, the increase in the diameter of the valve head to compensate for valve seat wear. To know the measurement of the valves of your engine, you must measure the diameter of the valve head with a caliber and compare it with the original diameter. For example, if the original diameter of the intake valve is 48,665 mm and the measured diameter is 48,815 mm, the valve measurement is +15

, the measure that they are mentioning probably refers to the size of the valve in millimeters in relation to the cylinder diameter. In general, when talking about measures such as +3, +5, +15, etc. It means that the valve is slightly larger than the standard diameter of the cylinder. This can affect engine compression and performance, so it is important to choose the correct measure to guarantee a good operation.
hydrotherm-bombasyplantasvenezuela.com.ve/index.html