Leakdown problems after valve job (long)

[Jay Whitely]

Hey guys,

On a customer's car, I recently did a fresh rebuild on
his S13 Silvia DET motor.  Part of the rebuild of the
head involved a 3 angle valve job, resurface, and
polishing of the combustion chambers.

When I went to pick up the head, I noticed they had
forgotten to polish the combustion chambers.  So, they
went in and polished them AFTER the valve job (valve
seat work) was done.

Another note: I wanted to assemble the valve seals,
springs, retainers, etc...myself. So, they gave me
back the head with the valves in the head but not
fully assembled with the above mentioned hardware.

The machine shop says they test all their heads to
hold 30 inHg of vacuum before leaving their shop. Can
they still accurately perform this test without the
valve springs pulling up on the valves?

Now to my point: After assembling the motor,
installing it into the car and putting about 15 miles
on it to seat the rings, I did a compression and
leakdown test.

Here were my results:

1. 100 psi, 66% leakdown, intake valves
2. 135 psi, 30% leakdown, intake & exhaust valves
3. 107 psi, 67% leakdown, intake & exhaust valves
4. 135 psi, 19% leakdown, intake & exhaust valves

I then removed the cams completely from the engine and
retested with very similar results. This eliminated
the cams and/or HLAs from the equation.

So, on all 4 cylinders, I am getting leakdown through
the intake and exhaust valves.

Several machine shops have told me that the machining
may have been slightly off and driving the car MIGHT
help to finish seating the valve seats.

The shop that did the headwork told that they vacuum
test all their heads and that I must have bent all 16
valves at some point. I really doubt I did this.  I
was apalled when the guy told me this, as if I was a 5
year trying to assemble an engine. He told me that no
amount of running will "ever unbend the valves".
"You're gonna have to pull the head and bring it back
in," he said.

This is an 8.5:1 CR motor with JWT S3 cams. Vacuum
gauge readings at idle, warmed up are 13 inHg, steady.

My only theory is that when they went back in an
polished the combustion chambers, they might have gone
astray a bit and affected the valve seats slightly.

My question is this: is it possible that in some
circumstances, driving the car might help seat the
valves a bit more or should they be perfectly seated
right from the beginning and they will never get any
better?

I would hate to have to pull the head again,
considering my customer has a $200 GReddy metal
headgasket in there.  Any advice would be greatly
appreciated.  For now, I am going to put a few hundred
miles on the motor, seat the rings, and restest later
to see how things look.

Thanks a lot guys,

=====
Jay Whitely
Tampa, FL
1996 200SX SE-R
GTi-R powered, F-MAX Stage 2