[s-cars] Engine completey hosed

Sun Jan 18 14:11:51 PST 2009

 I'm 100% on board with this theory.? It would explain why it sounded like detonation... because it essentially was.? Flame from #4 is preigniting #5... pounding the rings and piston to destruction.? The same could be said for #1 and #2.

This idea sounds very plausible, and would explain why certain pistons are melting away.? 700 miles of this sort of thing would probably lead to what I now see.

Dave

-----Original Message-----
From: Calvin Craig <calvinlc at earthlink.net>
To: K Hayes <abiglizard at mac.com>; djdawson2 at aol.com
Cc: Audi S Car List <s-car-list at audifans.com>
Sent: Sun, 18 Jan 2009 12:49 pm
Subject: RE: [s-cars] Engine completey hosed

Kenny,

#4 fires just previously to #5.  The cylinder fires near TDC between the
compression and the power stroke.  We'll just assume it is at TDC for easy
math.  Of course this will cary by a number of degrees based upon engine
conditions and timing setup of the individual car.

Since all cylinders fire every 720 degrees of crank rotation the separation
between consecutive firing events, which #4 and #5 happen to be, should
nominally be 144 degrees of crank rotation.  This means that the piston in
number 5 is approximately 36 degrees after bottom dead center and therefore
a good way into its compression stroke at the time #4 fires.  Now, what we
know about a compression stroke is that it doesn't build much compression if
the valves are open.  Ok, I'm being a smartass :)  Depending upon cam
timing, which I don't have readily at my fingertips for any Audi cam at the
moment, the intake valve will have probably closed some 30 to 40 degrees
prior to tyhis firing event.  Also, there is some time necessary for the
flame front to travel through the headgasket leak and into cylinder #5.

The point I am trying to make is that both valves in the #5 cylinder are
most likely closed, or damn closed to completely closed when #4 is firing,
which could create something akin to detonation in the #5 cylinder.
Although it is a bit different because the piston in #5 is most likely
further down in the hole than when normal detonation would occur.  I don't
know how this would make it worse or better on the piston, but I can tell
you it probably doesn't do anything good for the piston's longevity.

--Calvin

-----Original Message-----
From: K Hayes [mailto:abiglizard at mac.com]
Sent: Sunday, January 18, 2009 11:33 AM
To: djdawson2 at aol.com
Cc: Audi S Car List; Calvin Craig
Subject: Fwd: [s-cars] Engine completey hosed

When #4 was firing, #5 should have had a valve open, right?  So
expansion gasses would have either gone into the intake manifold or
exhaust manifold.  Exhaust manifold no problem other then weird back
pressure, but what would that do to the intake manifold and other
cylinders.  Dave, what does the intake manifold look like inside?

Kenny Hayes

On Jan 18, 2009, at 11:05 AM, Calvin Craig wrote:

I would think that the flame travel appearing as detonation and
therefore
putting downwards pressure on the piston as it was coming up may have
caused
the broken up piston.  Too bad we don't have individual pressure
monitors on
each combustion chamber :)

--Calvin

   -----Original Message-----
   From: djdawson2 at aol.com [mailto:djdawson2 at aol.com]
   Sent: Sunday, January 18, 2009 8:40 AM
   To: calvinlc at earthlink.net; forgied at shaw.ca; s-car-list at audifans.com
   Subject: Re: [s-cars] Engine completey hosed

   Eh...

   As they say, stuff happens.  Having the car flatbedded for 700
miles and
arranging alternative travel for the occupants probably would have
cost me
nearly as much as cleaning up this mess.  Part of me knew that when I
was
making the trip back home.

   I would agree that the flame travel is what caused the burn... and
that it
started with the headgasket.  But I am still wondering why it burned
up a
piston.  The damage to my head is very minor... nothing like the pics
in the
link that Dave F sent.  I am certain the head is repairable.

   Oh well... I did get 60k fun and fast miles out of it, and I'll
get many
more once I get this resolved.

   Dave

   -----Original Message-----
   From: Calvin Craig <calvinlc at earthlink.net>
   To: djdawson2 at aol.com; forgied at shaw.ca; s-car-list at audifans.com
   Sent: Sun, 18 Jan 2009 1:05 am
   Subject: RE: [s-cars] Engine completey hosed

Dave,

Is it possible that the headgasket breached between two cylinders
thereby
allowing the flame front to travel from one cylinder to another.
This would
explain the "detonation" because one cylinder would see it as a
pre-detonation event.  I could see how doing that for 700 miles would
cause
a problem.  That's the best hair-brained theory I could muster.
Sorry that
this happened to you.  It reminds me of my first engine rebuild I did
when I
was 17 and the engine let go when I was 18.  The stupid oil pump bolt
had
backed out and I wasn't running an oil pressure gauge.  So I would have
easily been able to fix it in time for just the price of an oil pan
gasket
but instead I ruined all the bearings.

--Calvin

-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com]On Behalf Of djdawson2 at aol.com
Sent: Saturday, January 17, 2009 11:50 PM
To: forgied at shaw.ca; s-car-list at audifans.com
Subject: Re: [s-cars] Engine completey hosed

  Holy smokes... that guy's is WAY worse than mine.? Mine is a very
small
"line" between 4 and 5.? I'd like to see his pistons, and I'd like to
know
why it happened at all.? The headgasket doesn't bother me... it's what
happened to the pistons that makes me scratch my head.

FWIW... it was an all metal headgasket, and I did use ARP studs.

Dave

-----Original Message-----
From: David Forgie <forgied at shaw.ca>
To: s-car-list <s-car-list at audifans.com>
Cc: djdawson2 at aol.com
Sent: Sat, 17 Jan 2009 8:06 pm
Subject: [s-cars] Engine completey hosed

Dave: Sorry for your loss.? Such failures are NOT uncommon, e.g.:

?

http://forums.audiworld.com/s4s6/msgs/253448.phtml

?

The problem could be a metal/paper headgasket (instead of the later all
metal gasket) or

it could be stretched OE head bolts (I sure Hap will chime in on that
note).? High boost

engines probably need an all metal head gasket and ARP head studs and
nuts.

?

But that is just an opinion.

?

Dave F.

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