Cliff---In defense of the machine shop that said your current springs
are OK, they probably are. The shop would be in a better position to
know your head thickness and rocker geometry, and whether there was a
chance of the springs now in place to bottom out.
On the other hand, cam grinders may like a certain spring to be sure
they're capable of closing the valve when the rpm's are at the upper
limit, and also strong enough that the cam follower will indeed follow
the lobe. (Too strong of a spring can be unneccessarily hard on the
valve train) If you can supply the cam people with enough details about
your engine to let them determine the spring, this should then give them
back the advantage.
The one burnt valve you experienced is more likely to have occurred from
the valve not closing. Insufficient (like zero) lash, for whatever
reason, can do this.
Spring binding shouldn't come into play here.
Dick
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