Why do we take the time to hone and properly size valve guides in Mamo Motorsports heads when some builders just test to see if the valves move freely after machining, and then assemble it? Too little clearance, there won’t be enough room for proper oil retention around the valve, which could lead to more friction, galling and wear, or seize a valve in the guide leading to severe engine damage.
Too much clearance, the valve can move around in the guide and over time create an hour glass shape, reducing service life and creating oil consumption, leading to a loss of power from not properly sealing on the valve seat of the head.
Having just the right amount of clearance is critical for both performance and parts longevity. That's why Mamo Motorsports takes the time to measure each valve guide in each head. We also measure the stem diameter of every valve to ensure proper valve fitment and sizing so its operation is precise and it seals perfectly. It’s #themamoadvantage
Here’s our method: we set the dial
bore gauge at .3150 (which is exactly 8mm) using a Mitutoyo setting ring (positioning the dial to read zero on the bore gauge). We choose this diameter because it’s right in the ballpark of what we are targeting for the final diameter of the guide, which takes into account the OD of the valve stem being installed.
The guide in this photo measures .3146, which is within the tolerance that we are targeting. The goal is to provide just enough clearance to achieve the proper oil film thickness around the valve. It's important to note that clearances will vary based on valve stem material and the intended application, but that’s a whole other topic.
