Imagine your engine valve is like a spinning top. For it to work perfectly, it needs to spin smoothly and stay perfectly centered. When we "resurface" an engine valve, we're basically giving it a fresh, smooth face so it can seal tightly. But two important things, "concentricity" and "runout," need to be just right for that fresh face to do its job.
Think of concentricity like this: you have a target with a bullseye. The valve stem is like the arrow, and the valve face is like the bullseye. For good concentricity, the center of the valve face needs to be perfectly lined up with the center of the valve stem. If it's off-center, even a tiny bit, it's like your arrow hitting the target off to the side.
Why is this important? If the valve face isn't perfectly centered, it won't sit evenly in its seat in the engine. This can cause a weak seal, letting gases leak out and making your engine less powerful. It can also make the valve wear out unevenly, which means you'll need to fix it again sooner.
Now, imagine that spinning top again. If it wobbles as it spins, that's like "runout." For an engine valve, runout means the valve face isn't perfectly flat or round as it spins. It might be a little bit high on one side and low on the other, or it might have a slight wobble. (egg-shaped rather than a circle shape)
Why does this matter? If the valve face has runout, it won't make full contact with its seat all the way around. It's like trying to close a door that's a little warped – it won't seal tightly. This can also lead to leaks, uneven wear, and a less efficient engine.
When resurfacing an engine valve, you're grinding a new, smooth surface on the valve face. It's super important that you pay close attention to concentricity and runout during this process.
By carefully controlling concentricity and runout, you will ensure the engine valves are as good as new (or even better!). This helps the engine run smoothly, powerfully, and last a long time. It's all about making sure those spinning tops are perfectly true!