Installing Perfect-Circle Valve Stem Seals

[jlandry@domain.elided (John A. Landry)]

Greetings fellow grim Reapers,

Something that I discovered last night while assembling the 392 heads on my
rebuild project made me think back to a comment that I *think* I read here
on the Digest.

Someone mentioned they either installed themselves - or had installed by
someone else - Dana Perfect-Circle rubber/teflon valve stem seals on their
valve guides.  As I remember, they had some reason to pull off the valve
covers where they discovered the valve stem seals were shredded and
destroyed.  This is sort of scary thought.

So last night I installed the new PC valve stem seals on the new guides I
had machined and installed in the heads.  Without going into a lot of
technical details, the instruction sheet that came with the seals explains
that you *must* have l/16" of clearance between the top of the seal and the
valve spring keeper when the valve is fully open.  If the original o-ring
seals are also used on the valve stems, this 1/16" clearance would need to
be taken from the bottom of the o-ring seal (which sticks out slightly
below the bottom of the valve spring keeper) to the top of the PC seal.

As I was preparing to assemble one of the intake valve springs, I checked
this seal to retainer clearance by using a dial indicator to measure the
appropriate valve lift.  What I discovered was that the valve *could not*
be fully opened before the o-ring (or valve retainer if the o-ring wasn't
used) would contact the top of the new PC seal.  In short, the valve guide
- in it's stock height - is too tall for the PC seal.

I had machined my valve guides on a small bench lathe using PC's special
cutting tool *prior* to installing the new guides in the heads.  This tool
is designed to turn down the OD of the guide so the new "cup" style seal
can be fitted to the shoulder.  A lathe is not required as the tool is
designed to be used with a hand drill, but since the new guides were not
yet installed and the lathe was handy, I decided to go ahead and do it that
way.  During the cutting process, I took special care to make sure I didn't
reduce the length of the valve guide any more than needed to just square
off the end where the seal would go.  The cutting tool is designed to cut
no only the OD of the guide, but will also cut the end if you get that far.
The cutting tool will easily reduce the guide OD *and* reduce the length if
you want to.

I installed the new guides to the exact depth specified in the IH shop
manual using a hydraulic press.  It was not until last night that I
discovered I should have cut the guides shorter and then pressed them
deeper into the head to give adequate clearance for the new PC seals.  I
can *easily* see how this would be overlooked by anyone... especially
someone not familiar with these seals and how they fit the guide.

In it's factory configuration, it appears IH designed the valve guide
position to give 1/16" clearance between the top of the guide and the valve
stem o-ring.  So anything added in between without machining the valve
guide is going to eliminate that clearance.  The teflon insert in the
center of the seal is approximately 1/8" thick, so the valve guide must be
reduced in length by approximately the same amount to retain what seems to
be a standard 1/16" clearance.

For the person that had their seals destroyed, I'd sure think this might be
the cause of the problem.  If the valve guides were simply machined in the
OD and not length, the new seals would be crushed and destroyed in just a
few engine revolutions.  Again, the instructions that came with the seals
aren't the most clear about this and I can see how it would be overlooked.
When you install the seals with the valves closed, it looks like you have
plenty of room.  It's not until you attempt to open it to the proper height
do you discover you have a problem.

I just thought I'd warn everyone about this in case you are contemplating
having these newer style seals installed during a head or engine rebuild.
Make sure you double check your own or the machine shop's work.  And if you
install an aftermarket cam with higher valve lift... you may have a
problem... Perfect-Circle seals or not!  If the valve lift were increased
by 1/16" and nothing else, the clearance between the factory style valve
stem seal would be eliminated and the seal would be smacking the top of the
valve guide.  Anything above that and the stock valve spring retainer would
be smacking the valve guide.

So at lunch today my project is to reduce the length of all my intake valve
guides by approximately 1/8" using the Perfect-Circle cutting tool and a
huge slow turning drill press we have at work.  But again, a variable speed
1/2" capacity hand drill would also work.

Best regards,

John L.
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