[V8] Noise that is driving me absolutely CRAZY!!

[Paul Jager]

I would start by looking in-depth at all the clues that you've got
available, getting them all down and then looking at what is behind the
clues, before stepping to the diagnosis phase.

For example, these things happen with heat:

Clearances decrease (between moving parts),
The block expands, belt tension increases (if not properly compensated for)
Grease/oil viscosities decrease
Rubber and plastics get more pliable.
Oil system flows more freely
Cooling System pressurizes
Combustion system leans out as cylinder temperatures increase.

As per the blurb below the diesel sound itself is more a pressure wave
noise.


Paul Jager
www.jageng.com

The noise produced by a diesel engine is a combination of combustion noise
and mechanical noise. Fuel properties can affect only combustion noise. In a
diesel engine, the fuel ignites spontaneously shortly after injection
begins. During this delay, the fuel is vaporizing and mixing with the air in
the combustion chamber. Combustion causes a rapid heat release and a rapid
rise of combustion chamber pressure. The rapid pressure rise is responsible
for the diesel knock that is very audible for some diesel engines.

Increasing the cetane number of the fuel can decrease the amount of knock by
shortening the ignition delay. Less fuel has been injected by the time
combustion begins and it has had less time to mix with air. As a result, the
rapid pressure rise, along with the resulting sound wave, is smaller.

One design approach to reducing combustion noise is to shape the injection -
setting the rate slow at first and then faster - to reduce the amount of
fuel entering the cylinder during the ignition delay period. Another is to
use indirect-injection.




-----Original Message-----
From: v8-bounces at audifans.com [mailto:v8-bounces at audifans.com]On Behalf
Of kyle leatherwood
Sent: March 19, 2006 6:25 PM
To: v8 at audifans.com
Subject: [V8] Noise that is driving me absolutely CRAZY!!


Ok everyone.  I have officially gotten tired of hearing this abnormal noise
that my 91 V8 5 speed makes.  This noise ONLY appears when the engine gets
to operating temperature. Between startup and operating temp, the engine is
as quiet as a mouse (a tiny bit of lifter tick on occasion).  This noise
sounds like there is a freaking diesel engine under the hood.  Engine has
had entire t-belt service done with new bearings and rollers all around.  I
have pulled both valve covers and checked cam chains, they are great.  I
have pulled off the serp belt to eliminate accessory noise.  Odd thing is
that Mark Willoughby's 4.2 5 speed makes the exact same noise.  Keith at
Germanautoconnection says he rebuilt the entire valve train on a 4.2 once to
try and eliminate the noise, but to no avail and told me not to worry about
it.  Car drives beautifully, no loss of power of any kind.  AARRGG.

Anyway, as anal and picky as I am about my vehicles, this noise is driving
me nuts, so I must find out what is causing it.  My 1990 with 130,000 miles
makes no noise whatsoever, and this one only has 116,000 on it.

Has anyone out there run into this and found out what it is??

Any help with finding this out will save my sanity in driving this wonderful
vehicle.

thanks,

Kyle


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