Doing the Subaru heads specifically for oversize valves I finish the seats on the mill as described here.
 
-I'm using Sioux tapered pilots and I run'm down in as tight against the taper as I dare with a little oil to keep'm from galling.
 
-I have used a small diameter spring on the pilot down to the valve guide to keep some pressure up against the bottom of the ball driver---but I found that the steep shape of the valve bowls creates problems finding mall enough springs and you can't get a brass lower button onto the spring because the step of the Sioux guide pilot is right there at the top of the guide in the bowl.
 
    So I fabricated a special spring out of .090" spring steel wire---that pulls the ball driver up to and holds it in place inside the ball socket---by reaching up and clamping from the ball socket driver that's in the mill quill.
 
-To make this work really good I had to precisely slot some large diameter washers with holes slightly larger than the recessed neck near the ball head.
 
-I also had to machine a little off the upper part of the main body just below the recessed neck under the ball head to allow the washer to drop down away from the ball slightly and to make room for the wire diameter of the spring to slide in there real easy.
 
-Also had to machine a small amount off the ball cup part that's in the mill quill to allow the spring a little extra clearance---just so the spring is easier to get in and out.
 
-I slip the washer onto the neck and slightly squeeze it in a vise and that crimps the washer so it stays in place.
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    This idea requires removing the spring every time you pull the ball driver up so that you can remove the ball driver from the drive socket.
 
-Even tho this is a little slow it now allows me to grind/slant the bowl end of the intake guide---where that absolutely would not allow a common spring arrangement on the guide pilot.
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    My process is sort of complicated to explain but I set up using a small round level sitting on top of a valve head to get the tilt of the heads in the ball park----then a collet with a rigid pilot to get the baseline of one hole.
 
-I built a dial indicator mount that clamps to the OD of the ball driver---where this indicator is mounted on a 45º angle and has a small point so that I can see the point against the seat area.
 
-I go thru and center up on all the seats and get numbers for the digital readout for all the seats.
 
-I also have another dial indicator mounted on a bridge---like you'd use to check valve depths-----so I drop a stock valve in onto the stock seat, get a number at the outer edge near the margin-----and since I'm typically only doing oversize valves (and Subaru heads) I temporarily set a new valve onto the stock seat----to get an idea of how deep that valve seat needs to be cut.
 
-Part of this can involve checking the overall valve tip lengths where the valves stock thru on the valve spring side for valve lash considerations
-and maybe slight alteration considerations there.
 
-I also number each chamber and I engrave the position of each valve as 1F & 1R----3F & 3R etc so that each valve has a respective seat.
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 The slowest I can run the mill is 60rpm and that's what I've found to be best so far.
 
-Then I start to cut the bowl and as soon as I see the new 45º show up---which is about .012" from my final target depth----I might stop and check that 45 with my runout gauge----or I have usually been able to go to within .006" of target depth.
 
-Measuring the seat runout with a tapered pilot is a trick----takes some practice and some belief in the fact you THINK you are getting good readings---but I pretty well feel confident that I'm in the ball park.
 
-So I measure the runout----usually have always been within about .004"---so I'll adjust the mill table slightly using the digitals----mark the seat and scrape the surface clean again.
 
-When I get the seat runout where I want it---usually within .003" of target depth----I take the first valve and use a little lapping compound to verify the seat laps in in just a few strokes and that the valve face lap line is where I want it.
 
-Then I'll drop the valve in and get a depth measurement again to verify exactly how deep I need to finish up at----and go ahead and cut that final depth.
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    I cut'm dry----and I use a little air blast to cool the tool a little just as I stop the cut---or sometimes I will roll the quill back up depending on how the cutter is sounding.
 
-The Subaru seats cut almost exactly like cast iron---maybe a hard cast iron---but they cut real nice and I don't have any chatter.
 
-I also use a 75º cutter set up on a different ball driver to enlarge the intake bowls then I hand blend the intake bowls and back up into the ports with a carbide burr and polish the carbide burr marks out----leaving a short amount of the 75º showing below the seat.
 
-I use another ball driver all set up for the exhaust seats---and this has a nice roll off the bottom of the 45º seat into the bowl.
-I virtually always hand blend ALL exhaust bowls right up to the bottom of the 45º seat cut with a nice shiny smooth finish.
 
-I have been able to get the seats depths all within .0020" total variation on each head---and after doing 5 sets of heads right in sucession I find there is only about .004" variation among all those seats depths.
 
-I feel that the seats  would all show less than .0010" total indicated runout when measured by any other persons methods.

Machining Subaru Valve Seats

Bill Jones' Photo Gallery Page 14

Bill Jones' Photo Gallery Page 14