I knew I was going to get in trouble with that post about NGK BP6ES vs
BPGES-ll plugs.
I shall explain further. The BP6ES were designed with gaps of .035"
max in mind. When electronic ignitions that could fire larger gaps came
along it was seen that the end of the center electrode and the lower
surface of the ground electrode were no longer parallel with each other
when gaps of over .035" were used. This "slanted" gap meant that the
plug would erode quickly at the point of the smallest gap. So, the
plugs didn't last as long because they were firing across the small area
at the smallest gap and eroding the metal at that point. Resut? The
ground electrode quickly burned away and misfire occurred diu to the gap
increasing.
So the -ll NGK plugs appeared which have a longer ground electrode
which can be bent around a longer curve and still stay in the proper
relationship to the center electrode. The same thing applies to plugs
made by any mfr for electronic ignition engines.
Now there are plug-gappering tools that reform the ground electrode as
the gap is adjusted (kind of a die tool). Problem is that the ground
electrode may not extend all the way across the center electrod after
this operation.
Conversely, if you use the -ll type plugs and gap them to, say. .032",
the electrodes will be misaligned the other way.
So, ya hafta get the plug for the gap you wanta run.
CR
Paul Hunt wrote:
>
> Haynes says 25 for the 25D4 and 35 for the 45D4 and 45DE4. 40 is not
> unreasonable for a sport coil. Never heard of 'large gap' plugs, the
> single-electrode Champion and NGK I use are adjustable for any gap I have
> ever heard of.
>
> PaulH.
>
> -
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