[SEL] Spark Plug Design (Check This Out)

Jim Hardman jim at hardmanfamily.net
Fri Jun 29 06:40:10 PDT 2007


Like so much in life, there's not much new.  Pre-combustion chambers in spark plugs have been touted since 1915.  Mosler advertised their Vesuvius plug spouting a gusher of flame, pictured bottom side up against the backdrop of an erupting volcano.  The Mosler Spit Fire was a well made spark plug.

Closed-base plugs were legion;  common examples include Reflex No. 1, National Torpedo, S&M, Never Miss #8, Blue Blaze, Randall, Sunderman, Comet, Inner Fire, EverReady Meteor, S&S, Bulls Eye (Conical Shell), Ball Multi, Janney Steinmetz, Vim, Sharp Spark, Hill 3A, Pep, The Ball, Mezger Torpedo, Reliance, Guide, H.P., Unique, Atlas, EKO, etc. etc.

Like the recent "Split Fire" plug with two ground electrodes, they didn't do much.

The idea of getting more spark to the combustible mix was also promoted by using two plugs at once;  a series plug installed opposite a standard plug (the hot lead ran through the series plug, then hard wired to the standard plug) allowed simultaneous ignition on opposite sides of the cylinder;  on some big L-head or T-head engines, where RPM was high and combustion chamber large, the concept had merit.

The one spark plug gimmick that really did work was an "intensifier" or external gap.  The coil had to produce higher voltage to discharge through two gaps in series and the resulting spark was "thick and strong" to quote the ad men.  When the working plug was partially fouled (current bleeding through carbon deposits on the porcelain or having to fire through oil on the points), the intensifier really did work.  Modern engines use this principle today... ignition wires contain no wire, they are carbon tracks promoting external resistance equivalent to an external gap.

Curt, you say that you have to clean your '55 Ford tractor plugs every time out... try an external spark gap.  These were originally little spacers fitted to the top of the plug;  gaps were sometimes visible inside glass sleeves or marbles, but often were open.  I have a few extra red fiber open gap examples if you want me to send a set to you.  Send your address off list.

Jim

Jim Hardman, Dorset
(A lonely conservative voice in green and liberal Vermont)

PS... It was good to meet Dave and other list members at Coolspring!



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