On this board and some others I am seeing two different specs for spark plug gaps. Does anyone know why, or would like to take a stab at why which one is more right than the other.

My book says .7mm-.8mm or around .030 inches.

Some others seem to be pretty sure that it is .023 inches. I'm confused.

I am using NGK BP6ES.

There does seem to be concensus on the points gap, between .012-.016.

Thanks
Eddie

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1965 220SEb Manual

Factory specs are the .023". The NGK plugs work well at .030". A wider gap will give a "hotter" spark to a certain point. It actually isn't any hotter but you have a longer arc which allows more of the air/gas mixture to come into contact with the arc. The factory specs were a "fail safe" gap for the older plugs.

my 67 250SL will not fire with the NGK and a .30 Gap,,, spent hours trying to figure out why I wasn't getting a spark.

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A Dalton

So would it be safe to say that I should widen the spark plug gap as much as I can for maximum efficiency? I assume at some point I will know when I have gone too far from some sort of missing or something like that and then I will go back down a couple hundreths. Is that the "advanced" way to do it?

I also noticed that the wider the point gap was, the higher the idle, and I believe, the better acceleration response, but if I went too wide I would start to lose power at high RPMs.

For instance, the points specs are .012-.016 inches. I just figured, okay that means .014 to be safe. But maybe I should go to .016 if it still runs well? Eh?


Should I also be going for the widest point there (points), as well, before I notice the power loss? Or do i jepardize something by doing so, i.e., maybe the car runs too hot or I prematurely wear the points or plugs?

I don't have a dwell meter btw.

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1965 220SEb Manual

I don't have a dwell meter btw.
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>

You should get one..the problem with old distributors is the parts are worn and the factory gap specs op not usually get you the dwell you want..so , a dwell meter is best b/c it is the true open/close angle the car is designed for.
The big factor in point gap is the fact that gap has a direct effect on engine Timing...if you close the gap, you automatically advance the timing, and visa/versa.... so, get a dweel..see em them ebap for cheap cuz they are outdated.

..and always set the dwell before setting the timing w/strobe.

That is the correct way..but you can fool with the points and still get a satisfactory result..but why, when it is so easy to get it perfect.
.030 is fine on those plugs..if they oil foul, don't change the gap, go to the next heat range ..[ NGK heat ranges increase with numerical decrease.]

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A Dalton

i.e., NGK BP5ES are "hotter" than BP6ES. It works the same way with the newer NGK stocking numbers. A 7333 is hotter than a 7433 etc.

Widening the gap reaches a point of diminishing returns. If you set them at .035" then after a few hundred thousands of firing the gap will widen to .036" due to wear and metal transfer from the spark.

.030" is a good setting which will give you pretty close to a combination of peak firing AND longevity.

Point gap is an entirely different situation. The points are triggering the coil high voltage spark output. Too wide of a spark delays the firing and too narrow does not allow the coil to "recharge" it's electrical field. That is a very simplistic view of the process but close enough for understanding.

>

Yeah, another way of putting it...'Inverse' works too, and Bosch are the opposite..higher/hotter.

These ignitions were not High Energy by a long shot, so I never go beyond .030 on any of them..and the spark heat is higher at a lower gap, but the kernal time is longer at a larger gap..so, a better idle is gotten with a larger gap...with .030 being close to ideal, with a Non resistor plug.

The best bang for the buck on any of these old ign systems is to simply do a point conversion and be done with mechanical switching...it's history.
Short $$$ - Big Reward

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A Dalton