plugs for D

jbk · Oct 22, 2014

what is the hots plugs you can put in a 38 d I have problem getting it to start if I would put a hoter plug in it would this help the problem or not

John T · Oct 22, 2014

If it has the older bigger 7/8 Plugs, I highly recommend the deep reach hotter side wire electrode Autolite 3077 or its equivalent.

If its the later smaller 18 mm (I dont think so) Id use the Autolite NON Resistor NOT the 386 or 388 Resistor plugs ESPECIALLY for a Magneto Ignition.

Sure, a good plug and its temp makes a difference, but a good strong HOT BLUE spark and precise static start timing out of the mag is more important then plug brand. Also, to reduce black carbon sooty fouling on plugs, use t stats or air curtains etc to get and keep the temp to 180 and over and dont run the carbs richer then necessary.........

John T

Lee B · Oct 22, 2014

<a href="http://aftermarket.federalmogul.com/en-US/Technical/Documents/Champion%20Spark%20Plug%20Copper%20Plus%20Heat%20Range%20Chart.pdf" target="_new">Champion Spark Plug Copper Plus Heat Range Chart.pdf</a>

I use D21 with no problems over 20 years at a time in my 44 A. Still don't know what you have now which would be a start to heat range selection.

I answered John T on purpose so you see HIS sage advise before mine. Can only repeat that if you have a mag you need non-resistor plugs and real copper wire in your spark plug wires to get every bit of the spark made on inside to the combustion chamber.

John T · Oct 22, 2014

"if you have a mag you need non-resistor plugs and real copper wire in your spark plug wires to get every bit of the spark made on inside to the combustion chamber"

I AGREE EXACTLY

No need to waste any precious energy in the form of I Squared R Heat loss in resistive plugs or resistive plug wires, I prefer to discharge it across the spark plug gap to ignite the fuel.

The thing is if those tractors were used like they were in their day pulling a heavy load at full RPM for hours on end the plugs wouldn't carbon soot foul like in todays light wimpy parade use lol That's why a hotter plug (Regardless of brand name) and getting the engines up to 180 and over can help.

Fun chattin with ya

John T

RandyB(MI) · Oct 22, 2014

Hey John T ! just a question about the side wire electrode 3077. Application / '37 JD A. JD book says .020 plug gap. In your experience would it be same if using this style plug or might one go more. Has Wico "C" , points set using "edge gap" method. Runs nice ,just wondering. RB

John T · Oct 23, 2014

Id say that relatively narrow plug gap is more concerned with Magneto use and doesn't really have anything to do with what plug you use (side wire or conventional). The coil ONLY ramps up to a high enough voltage to arc jump current across the plug gap and less gap means a lower voltage is necessary to arc current.

That being said, one hears antecdotal evidence that a wider gap makes then idle smoother (perhaps???) but I wouldn't bet the farm on that. I usually ran a tad wider maybe 0.025, but with a mag ignition, you don't want to get too extreme and if the mag (has a lot to do with its coil) was designed to operate best with a narrower gap like 0.020, that doesn't change regardless if the plug is conventional or has that side wire, 0.020 is still 0.020.

John T

RandyB(MI) · Oct 23, 2014

Thanks for the info , John , I / we all appreciate all your informative posts on here. RB

John T · Oct 24, 2014

Youre welcome, thanks for the kind words. As a retired engineer and technical writer and now an attorney, I say why explain something in a few words which I can stretch out into whole paragraphs lol lol

John T

plugs for D

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