[Farmall450]

Originally Posted by ol'George

It depends what one is working on, some seats are *30, others, *45 or *46.
An interference fit of *1 is not uncommon, I have never noticed much of a difference in longevity or performance.
But too large of a seat width can cause carbon to build up allowing valves to burn.
Too narrow of a seat area can cause excessive heat in the valve causing warpage/breakage.
Best to stay with the particular engines recommendations.

I have dressed small diameter stones down smaller, for a little 3-5 hp engine and purchased larger stones for a big valve engine.
With the quick way style one usually needs more $$$ to go bigger or smaller,
Cutters are not inexpensive,
also some heads are shrouded more than others.
It all boils down to what the mechanic usually works on.
Different tools for different mechanics and engines.
If a shop usually works on small lawnmower engines a few cutters will usually be suffice.
But not for a mechanic that might do a large displacement engine one day and a small compact vehicle another day.

Usually an interference fit of *1 is accomplished with a Valve ground at *45 and a seat cut to *46 as the seat stones are easily dressed *1 difference.
But making both *45 and paying attention to the width will work just fine, under normal conditions.

Now if one wants to do a 3 angle valve seat job, stones are easier to accomplish that, as you can set the seat width exactly in the center by
using different degree stones.
OR if building a engine that turns high rpm's and needs to breathe better but is limited on valve diameter, one can cut the seat to just hang the valve on the outer edge and increasing the bowel diameter(and flow) but still staying within the rules of a particular valve diameter.
These old skool things we did back in the day when factory or aftermarket parts were not available,
Today, a click of the mouse and a pocket full of $$ gets a person a lot of performance and/or power, and economy.
Sorry off topic again.

No worries, all good information. I agree that it's rarely done today -- cheaper to buy new valves than have a machine shop cut them.