Date: Sat, 22 Feb 2003 19:23:42 -0600
Reply-To: Stan Wilder <wilden1@JUNO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1@JUNO.COM>
Subject: Re: Correct Gap of Sparks
Content-Type: text/plain; charset=us-ascii
I watched this link and everybody had real good explanations as to why
the gap should be so-and-so.
Everybody pretty much understood and explained the way a spark coil
works.
Nobody explained how you can expect perfection from goodly used 20 year
old distributors, coils and timing gears.
I think the subject got nailed soon after it was posted and it always
comes down to ........ things change in the real world, coils get weak,
points get burnt or worn, distributor caps build in the electrodes and
rotors collect metallic debris.
Heavy arching in the cap between the rotor and distributor contacts will
indicate too wide of a spark gap or additional gaps as in the wires
described below.
With air cooled I often find that the wire going into the porcelain
(plastic/Bakelite) spark plug end has been threaded on to such a degree
that the wires have all been cut and another spark gap is established. In
most cases this is visible by the burnt Bakelite where the wire screws
in.
I've also found the brass connectors that push over the threads on the
plug are broken at the weld but still appear to be working correctly,
again it is visual with a burn at the location the weld would be.
Most people don't find these things or experience the problems because
they don't work on twenty different vans in a year.
An Oscilloscope would find these things.
An Ohms meter will find them too.
Stan Wilder
On Sat, 22 Feb 2003 23:54:37 -0000 Clive Smith
<clive.harman-smith@NTLWORLD.COM> writes:
> >Very cool that you guys can give birth to a link like this and keep
> it
> going for three days and still have no clear resolution to something
> that
> you can't control or modify anyway.
>
> Well Stan,
>
> Can't say I can agree with you there. I think with a few excellent
> contributions, we pretty well nailed it!
>
> 1) For all intents and purposes, despite what had been asserted by
> quite a
> few, it was established that changing the spark gap between nominal
> limits
> would struggle to change the timing by even one degree, probably a
> lot less.
> 2) The mechanisms for this slight change were established, which
> reside in
> the coil's secondary windings' Inductance, and not much else.
>
> .. and I wasn't really suggesting there was anything technically
> clever,
> advanced, or alarming about running large plug gaps, just that for
> differing
> reasons, its been a trend (or fad) from time to time that I've
> noticed. And
> that they quite often return to more common plug gapping in their
> next
> generation. I've no idea what the state of play is today, other than
> that F1
> probably leads the way with flame throwers.
>
> Clive
>
> ----- Original Message -----
> From: "Stan Wilder" <wilden1@juno.com>
> To: <clive.harman-smith@NTLWORLD.COM>
> Cc: <vanagon@GERRY.VANAGON.COM>
> Sent: Friday, February 21, 2003 12:24 PM
> Subject: Re: Correct Gap of Sparks
>
>
> > some production engines even going so far as 0.035" plug gaps
> (maybe
> > Audis?, can't remember, or maybe in BL's mad days!).
> > -----------------------------
> > My Oldsmobile plugs gap at .065 , seems it was no mean feat for
> GM.
> > Unless you've got all new parts on a laboratory engine you're
> wasting
> > your time trying to locate nanoseconds.
> > Very cool that you guys can give birth to a link like this and
> keep it
> > going for three days and still have no clear resolution to
> something that
> > you can't control or modify anyway.
> >
> > Stan Wilder
> >
> > On Thu, 20 Feb 2003 23:38:29 -0000 Clive Smith
> > <clive.harman-smith@NTLWORLD.COM> writes:
> > > Right, thanks Steve, point taken - I'm a bit hot off the mark,
> > > perhaps I
> > > should be more diplomatic
> > > .. whatever it is, I doubt if opening up the gap to extremes
> ever
> > > cause
> > > symptons such as backfiring through the exhaust (retarded) or
> > > pinking
> > > (which was being suggested!), provided the timing was pretty
> spot-on
> > > with
> > > new correctly set plugs.
> > >
> > > The most sensitive engine I've ever come across was a 1293 cc
> Cooper
> > > 'S',
> > > with 12:1 compression ratio. These distributors had no vacuum
> > > advance and
> > > generally showed pretty accurate centrifugal advance curve, with
> a
> > > single
> > > kink, where the stiffer of two springs took over. 1 degree
> advanced
> > > on
> > > static setting and it would pink badly, one degree retarded and
> it
> > > would pop
> > > or even backfire when lifting off between gears - the later
> being
> > > preferable
> > > as it went like a scalded cat when spot on or slightly retarded,
> and
> > > real
> > > crap if even fractionally advanced. I find that many people run
> > > engines a
> > > bit too advanced for good pulling power when setting them up
> 'by
> > > ear',
> > > usually arriving at a setting ahead of the manufacturers,
> > > unwittingly.
> > >
> > > The fact that the timing probably moves the right way under
> high
> > > cylinder
> > > pressures and rich mixtures, might mean that someone, sometime
> > > realised this
> > > (in the coil trade) and being inherently inductive devices,
> they
> > > never felt
> > > inductance per se was particularly a design goal, it just comes
> out
> > > in the
> > > design to resist heat and a duff environment (oil cooled) as
> quite
> > > high.
> > > Many would say these things are never considered or known about,
> but
> > > I
> > > generally find that the work has been done sometime way back
> and
> > > conclusions
> > > drawn, decisions made, long since forgotten about.
> > >
> > > I thought there was a strong trend starting twenty or thirty
> years
> > > ago to
> > > make much higher powered ignition systems that would
> succesfully
> > > drive a
> > > spark across bigger gaps, some production engines even going so
> far
> > > as
> > > 0.035" plug gaps (maybe Audis?, can't remember, or maybe in BL's
> mad
> > > days!).
> > > The arguments here are obvious, mainly stemming from igniting
> weaker
> > > and
> > > weaker mixtures for economical cruise with the larger spark
> that
> > > should
> > > ensue when it does finally jump - though maybe that trend has
> > > diminished due
> > > to starting and poor running problems when a 0.032 or 0.035
> gap,
> > > missing a
> > > service, becomes 0.037 or even 0.040" - and the consequent bad
> > > reputation
> > > gained.
> > >
> > > Clive
> > >
> > > ----- Original Message -----
> > > From: "Steve Delanty" <laurasdog@WEIRDSTUFFWEMAKE.COM>
> > > To: <vanagon@GERRY.VANAGON.COM>
> > > Sent: Thursday, February 20, 2003 10:24 PM
> > > Subject: Re: Correct Gap of Sparks
> > >
> > >
> > > > Clive,
> > > > Honestly I don't know what difference in delay or required
> > > > voltage would be between .025 and .030". It would all depend
> > > > I'm sure on the particular coil, and also on the pressure in
> the
> > > > combustion chamber at the time of firing.
> > > > Ignition coils have quite a lot of inductance and are pretty
> > > > slow devices as far as transformers go. I've played with a
> few
> > > > high voltage projects using ign coils to generate HV and they
> > > > don't work well at switching frequencies over about 300-400
> Hz.
> > > > It wouldn't surprise me if a change in plug gap of .010 could
> > > > change the firing delay by 10's of microseconds.
> > > >
> > > > I agree that the change in timing may be minimal, and that it
> > > > may be swamped by other factors (sloppy distributors), but
> > > > my point is it does make a measurable difference.
> > > > And every little bit helps, eh?
> > > >
> > > > If someone had some time with an O-scope and a high voltage
> > > > probe, it would be easy to put some real numbers to the whole
> > > thing.
> > > >
> > > > Steve
> > > >
> > > >
> > > > At 01:38 PM 2/20/2003, you wrote:
> > > > >Steve,
> > > > >Great, and thanks for some serious input. A breath of fresh
> air.
> > > > >Inductance has a lot to answer for...
> > > > >
> > > > > >At 3600 RPM one degree of crank rotation takes about 46
> > > microseconds...
> > > > >Changes in spark gap can definately make small but easily
> > > measurable
> > > > >changes in timing.
> > > > >
> > > > >a) So what is the difference between a 0.025" and a 0.030"
> gap
> > > (typically,
> > > > >assuming the ign. system will indeed fire across 0.030" gap
> > > > >Unless its of the same order as 46 micro secs then the
> timing
> > > effect is
> > > > >negligible as few can set timing to within 1 degree, even
> today
> > > and not
> > > long
> > > > >ago that same oscilloscope would show the centrifugal and
> vacuum
> > > advance
> > > > >mechanisms splattering the timing across a huge range, maybe
> +/-
> > > 5
> > > degrees
> > > > >of the mean (design) curve, in a bad dizzy.
> > > > >b) So this effect effect would have no relevance to a
> capacitor
> > > discharge
> > > > >system?
> > > > >c)... AND, everyone, this effect is BENEFICIAL, as far as
> timing
> > > goes
> > > (not
> > > > >spark quality). Because, as the charge volume and BMEP
> increase
> > > the spark
> > > is
> > > > >retarded (guessing at 1/20th degree!) and as we lift off,
> the
> > > spark
> > > > >advances - - exactly what the vacuum advance system does,
> 'cept
> > > it moves
> > > the
> > > > >timing 100 or more tiomes as much.
> > > > >
> > > > >
> > > > >Clive
> > >
> > >
> >
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