I’ll still put knurling in the car lot repair category.  Knurling simply raises a very small area or strip on each side of the knurling groove to restore the desired clearance back to valve stem.  This is ultimately a very small percentage of the guide area and ends up not being a high mileage repair.  If the camshaft is a performance grind with higher than stock lift, then the wear problem associated with knurling becomes compounded.  If the guide is worn enough to need repair, then guide replacement is at the top of my list.  I’m simply more partial to screw in bronze guides over other guide styles as their success rate and longevity is high in the applications for which I’ve used them.

Oversize valve stems would be a more desirable fix for worn guides as opposed to knurling as this would allow the surface area of the guide to be maximized.  Keep in mind that the guide area is where the heat is transferred from the valve to the head so anything (ie. knurling) that minimizes this area will keep the valve itself from cooling as quickly.  But off the shelf availability of oversize stems is decreasing as time goes along making this a less viable option.  As far as wear characteristics of stainless on bronze, the bronze guides themselves prefer additional stem clearance regardless of the valve material and this has to do with the expansion rate of bronze versus that of iron.

There are several different options regarding bronze valve guides ranging from a pressed in guide or guide replacement, a guide liner, and a screw in guide-insert.  Regardless of the type of bronze guide used, 0.0020”-0.0025” valve to guide clearance for the intakes and 0.0030”-0.0035” for the exhausts is preferred.  This is roughly about 0.001” more clearance than what you’ll find for iron guides in a new condition.

A disadvantage to the screw in guides would be their difficulty to replace after they’ve been installed but, ‘cross my fingers’, I’ve never had one go bad to date and I’ve been using these in my engines since the early Eighties.  The screw in bronze guide inserts are available from Atlas (Winona brand?).  K-Line makes a bronze guide liner with a spiral flute which have superior wear properties but these have been known to slip or become dislodged if the valve is subjected to extreme heat.

Daniel.  Haven’t seen the photo spread but that sounds like the screw in guide inserts to which I refer.  Atlas is the only brand I’m aware of for these.

My local machinist and friend, Bill Smith, started doing head work back in the '70s, and he bought a Winona brand guide and seat machine.  It sounds like the same guide inserts you are referring to, he bought them from Winona, but they could have easily been re-boxed Atlas inserts.  A little story about him.  Back in the days blueprinted heads began to show up on NHRA stockers, he was trying to break into the business then dominated by an Indianapolis shop.  I suggested that he offer to do a pair of heads for a certain Indy racer that could not quite run on the national record, and if the car would not then run under the record, he did not need to pay for the head work.  The racer agreed, the car immediately went a couple tenths under the record, and the next week Bill was inundated with sbc stocker heads from Indy.  I have often wondered aloud to Bill that I don't see how he makes any money, he's too finicky with his work for the prices he charges.  But he's been at it for 35 years.

John

Alan.  Takes more than a simple reaming to install sodium valves in place of standard valve stems.  For the Y engines, you’re talking about going from 11/32” to 7/16”.  Much of the time, we’re going the other way around in taking heads that originally had sodium exhaust valves and switching the valves out to ones with standard sized valve stems.  In these cases, new guides are installed.  Daniel was commenting on the oversize valve stems (0.015") that use to be available that simply allowed for the guides to be reamed and not require knurling.  As has been brought up, finding these valves for the Y with slightly oversized stems is now difficult by lieu of manufacturers sticking with the fast moving parts end of the business.

Daniel probably likes being called SUPREME but the name Supreme Being does get attached to the heavy posters on the board.