valve job question

[CLsnyder]

----- Original Message -----
From: William T Wilson <fluffy at snurgle.org>
To: <diy_efi at efi332.eng.ohio-state.edu>
Sent: Monday, May 03, 1999 2:23 PM
Subject: Re: valve job question


> On Sun, 2 May 1999, Shannen Durphey wrote:
>
> > > Cleaning the carbon deposits off of the piston isn't really all that
> > > important because they just come right back when the engine runs the
next
> > > time.
> >
> > Sounds like a tire shop I went to once.  "No need to clean the mud off
> > the wheel before we balance it.  It just gets muddy again anyway."
>
> Heh.  No, that's different, because the carbon deposits don't affect the
> operation of the engine.  Really.  Unless there's so much of it that it
> causes dieseling.
>
> My suggestion is more akin to saying "no need to clean the mud off the
> wheel before you rotate the tires."
>
Actually, carbon deposits CAN affect engine running. Compression ratio is
increased, making the engine more prone to detonation. If the cabon starts
to flake you get hot spots, making the engine more prone to detonation. Soft
carbon absorbs some fuel, causing cold low-speed driveability problems and
causing engines to fail sniffer tests.
Coating the cyl wall with grease before bringing the piston to TDC  for
decarbonizing was standard procedure - along with washing the cyl walls and
rings down with ATF any time a head was removed to remove ALL traces of
glycol from the rings before re-assembly. Glycol on the rings can cause an
oil consumption problem on an otherwise OK engine very quickly.
25 years as an auto mechanic - a good number of rebuilds, valve jobs, and
decarbs under my belt. Never a problem with ring / cyl damage.
> :}
>
>