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Q-authority:
I did some math and measurements. And here's what I came up with
Typical valve stem diameter .2310" (both Int. and Exh.)
SI valve guide interior diameter .2362"
O.K., subtract the valve stem diameter from the Valve guide diameter and you get .0052"
So let's round that number off to 5/1000ths.
The factory clearance for valve stem to valve guide is less than 1/1000. Now double that clearance number when you apply it to my previous math (because its less than 1/1000th X'2 to account for both sides of the valve stem).
The SI valve guides appear to be out of tolerance (worn out) new, right out of the box.
The BGB recommends using a 6mm Taper Reamer to ream out the valve guide. 6mm is .2329" a reamer of this size would pass through the SI valve guide without touching the inside of the guide.
I don't mean to sound uppity, or act like a monkey with a handful of poop . . . . . but I'd reconsider the SI brand choice.
In the small town where I live, I garantee that no machine shop would be able to do a 4ag valve job. They'd run a 1/4" (.2457")drill bit through the guide and congratulate themselves on what fine work they done did.
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