NG engine making a knocking noise when cold and ocassionally when hot.

[rob hod]

    Robert,
 A quick summary of the little I know about bad big ends, see how much seems
to apply to your case;

    Usually not a very deep sound, with the hood up it sounds a bit like a
small hammer(s) being rapped smartly on the block or similar large dense
steel object.
    Using the BF screwdriver as stethoscope (blunt end in ear , sharp end on
object) you can eliminate other areas by revving and listening.
    Rattle on startup until oil pressure builds
    Rattle when hot due to oil thinning and localised pressure loss
    Oil pressure won't necessarily read lower on the gauge, cos it may not
be much lower at the point that it is measured.
    Usually you can find a rev setting where they rattle, try holding
different revs (car stationary and in neutral) and see if theres one rpm
where the noise is particularly prevalent.

    Main bearings dont rattle, they 'rumble' or 'groan' for want of better
adjectives.

    Assuming you want to keep the car;

    If it is the case that the big ends are gone then the only proper repair
is to remove crank (and hence engine?)and assess for damage/deposits which
would mean a repolish or regrind in addition to new bearings.
    Often when bearings fail they leave their soft metal lining on the crank
journal or score it. Any such imperfections would destroy new shells so
quick you would cry.

 If  the mains were ok you should be able to get just the big ends polished
or ground.

You need to be very happy about the people you take the car to, as once its
apart you are in their hands with a dismantled engine.  Any good shop knows
the sound of bad big ends *without* dismantling the car! Maybe you should
try and get a second opinion or third before you let the engine be
dismantled

    HTH

rob
----- Original Message ----- > Message: 4
> Date: Fri, 12 Apr 2002 08:18:27 -0700 (PDT)
> From: Jim Green <jeg1976 at yahoo.com>
> Subject: Re: NG engine making a knocking noise when cold and ocassionally
when  hot.
> To: Robert Stirrat <Robert_Stirrat at DMCWave.com>,
> "'quattro at audifans.com'" <quattro at audifans.com>
>
>
> --- Robert Stirrat <Robert_Stirrat at DMCWave.com> wrote:
> > Hello,
> >          This is a question for the oily-handed
> > amongst you.   My 92 Series
> > III Coupe has started to make a knocking noise from
> > the engine, about five
> > or six knocks can be heard when I start it from
> > cold.  When I run rev the
> > engine by pulling the throttle cable, one or two
> > knocks can be heard.  It
> > sounds to me that the noise is coming from the top
> > end at cylinder 5.  There
> > is no loss of power or oil pressure from the block.
> >
> > I took it to a local garage, they had a look at it
> > and seem to think it
> > coming from the bottom end, and said they'd need the
> > car for two days to
> > drop the sump and check the shells.  Is this likely
> > to be the crankshaft
> > bearing shells or the connecting rod shells?
>
> If it sounds like somebody is wacking the top of your
> engine with a large hammer, it's probably a bad rod
> bearing.  It could be a crank bearing since the noise
> goes away when it warms up?
>
> > Is there anything else it is likely to be?
>
> Not really.
>
> > I should mention that I also had a ticking sound
> > from the lifters, this
> > prompted me to check the oil level.  Curiously, this
> > was below min, curious
> > because I had the oil changed some 6K miles ago, and
>
> Umm, 6k miles?  Your car could easily go through 2
> quarts of oil in that time, plus if that's you regular
> schedule, you probably do have some botom end wear.
> 3k miles is the max I ever go between changes.  My
> lifters always let me know around 2k miles that my oil
> needs changed soon.
>
>
> > also curious because I
> > don't have any leaks.  I topped up the engine with
> > .75 litres and the
> > ticking has gone.  You may also recall I had a
> > misfire on cylinder 1
> > recently which I sorted with a replacement lead.
> >
> > I'm telling you this as I am wondering any of this
> > symptoms were
> > contributary to the onset of my engine noise?
> >
> > Will the connecting rod and crankshaft bearing
> > shells be replaced as a
> > matter of course along with the sump gasket when the
> > garage carries out this
> > work?  Is there anything else I should insist upon
> > them replacing when the
> > have the bottom end apart?
>
> If they have to replace any bearings they will have to
> pull the crank out , which means dropping the
> transmission, or pulling the engine which would be
> best.  If you do have a bad bearing you want to make
> sure you get all the metal shavings cleaned out of you
> engine.  You may also look at a new clutch while your
> in there.
>
> HTH
>
> =====
> Jim Green
> '89 90tq EFI
> http://www.geocities.com/jeg1976/car_home.html
>
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