Owen_Dyneto Quote:
(snip)I would think a more correct definition of valve float is when the valves fail to follow the action of the camshaft profile on valve closure due to inertia of the moving mass.
Dave, that is a correct definition, particularly if you add that the failure to follow the cam profile is due to insufficient spring pressure above a certain RPM, a broken spring or some problem with the cam lobe. Also, on an OHV design engine it is ALWAYS the exhaust valve float that causes a problem because the piston is coming up in the bore just as the exhaust valve is returning to its seat. If there is valve float, the exhaust valve is "hanging out there" where it can be hit by the piston. This usually, but not always, bends the face of the exhaust valve, although sometimes it will also crack the piston top...both being a bad situation.
Tim Cole Quote:
The diameter of the spring affects the frequency. Larger diameter lower the frequency. That is why high performance motors have a smaller inner spring.
The first part of your statement is true, but it is not why high performance engines have a smaller inner spring that is an interference fit with the ID of the larger outer spring. It's the interference which reduces or eliminates the harmonics of the spring pair through friction. A single spring (large or small) will have its own harmonic which at the right open/close frequency can cause some of the coils to contact each other. Ignoring coil bind at max lift (which would break one or more springs immediately upon initial startup), harmonic caused coil bind does not happen with interference fit spring pairs (or triples for that matter).
Craig
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