I would ask for the tech man to show you in the rules exactly what was violated.
As Freezeman noted, I looked at three separate jr sprint / kid sprint rules and not one spec'd the ID of the valve guide, just that the guide can only be replaced with a Briggs guide. Now, if your builder replaced a guide with something other than the Briggs guides, that would be a violation, but that's not the reason that you/he gave.
.001" larger than what? Larger than what measurement? Larger than a brand new guide? That's not unreasonable due to wear.
Now, did the tech man see something going on that breaks the spirit and intent - undercutting the guide to puddle oil and reduce drag on the valve stem, something along those lines? (It wouldn't be .001, more like .010.") We don't know without seeing the part in question or hearing the tech man's side of the story.
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Thanks and God bless,
Brian Carlson
Carlson Racing Engines
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