A Salute to the Pros.

My kid just replaced the lower manifold gasket and upper plenum of his
'95 Bonneville - 3800 Series II.  Preventative measure due to many
catastrophic failures of those on that engine.
Car has 82k miles and is real clean.  Got it from a little old lady.
There were no problems except the tensioner was weak according to the
kid, so he put a new one on while we were doing the job.
New plenum has modified EGR stovepipe to eliminate melting and new
manifold gasket is aluminum framed versus plastic.
Job went well, and we took our time with everything.
Old gasket looked terrible with rot, and needed to be changed.
Plenum around the stovepipe looked ok, but who knows what the heat was
doing to the plastic.
I mostly helped clean parts, acted as gofer and provided what I knew
from many years of amateur wrenching on cars, including a couple
engine rebuilds.
I'm real particular about gaskets/gasket surfaces, the right dope or
no dope and torquing.  But I left him alone often, as he's real good
at wrenching, better than me.
Spent a little time on the computer getting the correct intake
manifold torque specs and tips.  The factory shop manual
has them at 89 inch pounds, when they're actually 132.
Disappointing that a shop manual is off like that.
After the engine reached operating temp a chirping started, at idle
only.  Intermittent, not steady.  Loud enough to hear 60 feet away.
Never heard anything exactly like it before, but it was close to
sounding like an accessory bearing.
But not quite.  Irritating as hell.
Couldn't pin down where it was coming from, even with a stethoscope,
but it sounded low on the engine.
I asked the kid if the new tensioner was a lot tighter than the old
one, and he said it was.  Told him to replace the water pump.
Wouldn't hurt, cost only 35 bucks for a new one,  and with 82k on
a GM pump, why not?
Besides, it wasn't the A/C compressor, alt or PS pump from our
analysis.
Back at operating temp, the chirp resumed.
Kid crawled all over the floor under the car and says he thinks the
harmonic balancer moves too much when he wiggles it.
So I look at the Bonneville forum, and sure enough, plenty of them
fail too, and sometimes cause belt chirping.  I never noticed the serp
not running true when hearing the chirping, so I didn't buy it, and
told him to take the car to a dealer mechanic.
Time to admit somebody else should take over the diagnosis.  But I
told him I would put the balancer on my card since he was tapped out.
That's what he wanted to do.
He's real worried, because he dumped maybe 1/8 cup of coolant in the
valley when he removed the manifold.  He changed the oil before
starting it again, but who knows.  I told him I've heard rod and cam
bearings go bad, and even wiped them into the crankcase, and they
don't sound like that, and get worse off idle, but now he's even
getting me worried.
Next day he calls me from work and says he put a new balancer on and
it's been 20 minutes and no chirping.  He's happy as a clam.
Everybody's happy.
Calls back a few minutes later and says the chirping has resumed.
Calls back 10 minutes later, says he's running it on the rack and has
pinpointed the noise to be coming from the rear engine or transaxle.
Now he's got my wife worried and depressed (mothers!), me worried
because I'm going to have to cash a CD to lend him money for a car,
and he's practically crying, thinking he's lost a really nice car.
But he's really calling me because he wants advice.
I told him again, this time with more force, "Take it to a dealer.
They work on these damn things all day."
Like I said, he's a good wrencher and has a bunch of those
AS whatever certs, but this is his first 3800.  He is really averse to
giving up.  Besides, he specializes in suspensions.
After work, still wearing his mech uniform he takes the car to a Chevy
dealership a couple blocks away, and since they're slow the service
manager has him pull right in.
A dealer mech is walking by, hears the chirping, and tells him to pop
the hood.  Pulls the oil filler cap off, and it sucks hard, almost
killing the engine, then it comes right back, and the chirping is
gone.
Pulls the PCV that came with the new plenum and tells the kid
he forgot to put the o-ring on it.  Happens to have the right o-ring
10 feet away and puts it on.  Five minutes total.  No charge.
The chirping was the rear main seal sucking air.  
Kid calls me on the way to the bank to get 40 bucks to slip to the
mech.  He's on cloud nine.  And a bit embarrassed.
But the whole family was happy again.
Somewhere there's a moral to that story.
Since I don't moralize, I'll leave what that is to others.

--Vic