Piston to valve Clearance?

[gvr4]

Do you deal with metals at those tolerances? If so, I'm sure you are aware of the changes that will occur over the temperature range seen by a component like a valve. 0 clearance at 70 degrees means -.025" or so at 600-700 degrees

There's also a phenomenon called valve float that really tends to make a mess out of things if there's too little clearance. It's easy to see how a pushrod engine would end up with quite a bit of valve float because of all the extra mass in the valve train. But valve springs in an overhead cam engine have a lot less inertia to contend with, and I'm wondering if this translates to tighter acceptable clearances.