Subject: Auto Conversion - Conversion
From: Rotary Engine
Date: 3/8/2007, 8:41 AM
To: AARotary Engine



     >> One more question Joe.
     >> Was the EM2 or the Microtec controlling ignition?
     >>
     >> Paul
     >
     >
     > I have the MicroTech. That's what Atkins sells with his engine
     > package. It seems to be a reasonably complete and robust system.
     >
     > Here's a picture of the broken sparkplug.
     >
     > Joe Hull
     > Redmond/Seattle WA, Cozy-Mark-IV - 71hrs
     >
     > Thanks for the picture Joe.
     >
     > I think a slightly smaller gap might prevent the broken ceramic
     > from dropping below the ground electrodes.
     >
     >
     > Paul Lamar ...No rotor no motor.
     >
     > That is a different spark plug from the standard 2nd gen
     > BUR7EQ-L/BUR9EQ-T? Looks more like the spark plug used on the first
     > gens?
     > Perry Mick

    Thanks Perry.

    Jim Mederer and Dave Lemon, have you seen this failure before.
    The supposition is the ceramic insulator failure took out the
    apex seal. Is this a common problem in racing engines?
    --
    Paul Lamar ...No rotor no motor.

    Hi Paul,

    A broken plug insulator usually means the plug was too hot,
    detonation - or both.

    Jim Mederer

    Thanks Jim.

    I know it is not a common problem in street engines as there
    have been over a million Mazda rotary engines sold and if this
    were or is a common problem I am sure Mazda not have sold a
    million engines. This plug was from a normally aspirated engine
    with 35 hours of high power running so detonation was unlikely.

    So keep checking your plugs guys when the engine is new
    to be sure they are not overheating and the plugs are of the right
    heat range.

    It is the duty of the engine builder to put heat range plugs in
    the engine that are consistent with its intended use. If the plugs
    prove to be too cold than adjustments can be made later.

    Jim, given this scenario what plug numbers would you recommend?

    Paul Lamar ...No rotor no motor.

Hi Paul,

    Many things affect heat range selection, so I can't give a
"recommendation", only guidelines.  Ultimately, for aircraft use, I
believe you are better served with the coldest plug that doesn't foul
excessively.  This gets wrapped up with the power of the ignition,
compression ratio, mixture, timing, cooling, plug gap, plug design, and
a lot of environmental factors.  As a rough cut, for a near-stock
engine, 2 steps cold from the standard heat range is a reasonable
starting point.  And beware;  Trailing plugs are more susceptible to
detonation than Leading.

Jim Mederer

Thanks Jim.
Here are the NGK plug part number codes
from http://www.math.uwaterloo.ca/~rblander/NGK.txt

Paul Lamar ...No rotor no motor.

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		NGK SPARKPLUG CODES
		===================


Here is the table of values for NGK spark plug names.

The breakdown is like this: [B] [CPR] [6] [E] [S] - [11]
Six fields.  Some, e.g. the second field, are optional.
Some fields may have multiple letters.

Field one: Thread diameter.
  A = 18mm      B = 14mm        C = 10mm        D = 12mm

Field two: Construction.
  C = hex size 5/8"     K = hex size 5/8 with projected tip (ISO)
  M = compact type      P = projected insulator type
  R = resistor          SD = surface discharge for rotary engines
  U = semi-surface discharge    Z = inductive suppressor

Field three: Heat Range.
  2 = hot, up to 10 = cold.  There's no 1, I guess.

Field four: Thread reach.
  E = 19mm      F = tapered seat
  H = 12.7mm (1.5")     L = 11.2mm (7/16")

  If this field is blank, an 18mm diameter plug has 12mm reach,
  and a 14mm plug has a 9.5mm (3/8") reach.

Field Five: Firing end construction.
  A, B = special design (no details given)
  C = special ground electrode
  G = racing use
  GV = racing use V type
  H = half thread
  K = 2 ground electrodes for certain Toyotas
  L = half heat range
  LM = compact lawn mower type
  M = 2 ground electrodes for Mazda rotary engine
  N = special ground electrode
  P = platinum tip (premium)
  Q = 4 ground electrodes
  R = delta ground electrode for BMW
  S = standard 2.6mm centre electrode
  T = 3 ground electrodes
  V = fine-wire centre electrode, gold palladium
  VX = platinum tip (high performance)
  W = tungsten electrode
  X = booster gap
  Y = v-groove centre electrode

Field Six: (after the dash) Wide gap.
  8 = .032"             9 = .036"               10 = .040"
 11 = .044"             there is no 12          13 = .050"
 14 = .055"             15 = .060"              20 = .080"


Other notes:
There's more, such as for metal shell plugs, "V-Power" plugs
for North American made cars, and other stuff.  I'm not typing it in.

Some Motorcycle-related comments...

Some bikes use the DR8ES-L plug.  Theres's no indication what the 'L'
means; it does not appear in the symbol chart for field six.

Seeing as I specialize in Honda V4 info...

ST1100 (hey, it's a V4) : CR8EH-9
VF1100 : DPR8EA-9
VF1000 : DPR8EA-9
VF750, VF700 : DPR8EA-9
VFR750, VFR700 : DPR9EA-9
VF500 : DPR8EA-9
VFR750R (1990) : CR9EH-9
VFR750F (1990) : CR9EH-9
VFR750F (1991-92) : CR8EH-9

Extended-life platinum tip plugs replacing the CR9EH-9 are
available as CR9EHVX-9.

Resistor plugs are used for two reasons --

 1. They cut down electrostatic interference.

 2. They provide a sharper "edge" to the voltage spike, making for
    a stronger, shorter spark. On high RPM motors, this is important.

The projected insulator simply describes the shape of the plug head.
A projected insulator sticks out a little further into the combustion
chamber.

--------------

I've proof-read this for typos and I believe it to be accurate
to what appears in the 1992-93 NGK catalog from which it is taken.

You can reach NGK at  800-855-8151 (?), 714-855-8278