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John Deere Tractors Discussion Forum
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Spark Plug Cross Referencing

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ol' guy

03-13-2006 15:08:59




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I attended a seminar on 2-cyl JD tractors last week and a couple of the "experts" highly recommend using the hottest plugs available in restored tractors used only for show, parades,etc., and not worked in the field. Is there a chart availble that shows the plugs for different models ( A,B,G etc.) by make and heat range? For example, what Auto-lite and A-C plugs are comparable to a D-21, D-23 etc. Champion?? Thanks for the help.

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JGC

03-14-2006 15:14:13




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 Re: Spark Plug Cross Referencing in reply to ol' guy, 03-13-2006 15:08:59  
Ah yes, the ongoing spark plug debate.

I decided to check a few new plugs I have in stock for my "D". All of the Autolite 3077s measure ~1 ohm using an old analog VOM which passes some current thru the circuit under test.
Imagine my surprise when I checked two brand new Champion W-20s and found that one measured ~3 ohms as expected and the other one measured in the low Megohms!
I didn't set up a test circuit to determine if the questionable W-20 would arch internally at high (magneto) voltage.

Tip - I rotate plugs between the left and right cylinders frequently. This does a nice job of burning off the deposits that accumulate on the plug in the "lazy" cylinder.


Regards to all!
Jon

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John T

03-13-2006 19:11:45




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 Re: Spark Plug Cross Referencing in reply to ol' guy, 03-13-2006 15:08:59  
At GOG last week both at my Magneto Ignition Seminar and Round Tables and at Cork Groths Seminar I recommended use of the Autolite 3116 as it is a NON resistor plug versus the Autolite 386 or 388 resistor plugs, and that afternoon Macks Tractor Parts sold out his complete inventory of the 3116 plugs I DESERVE A COMMISSION LOL

The older Deeres like other old tractors ESPECIALY when using a Magneto Ignition, were NOT designed for either resistor plugs or resistor wires. Those elements can reduce radio interference but are an added and unwanted load on the low energy ignitions and waste energy in the form of heat and I squared R losses versus discharging all the stored energy across the plugs gap where its needed the most. In addition the Mags have to work harder and can run at higher temperatures when one uses resistor wires or plugs !!!!! !!!

If we used the tractors as they were designed at full RPM and under a full load and at temperatures over 180 degrees, theres a chance the recommended heat range of plugs may yield that nice warm gray color. HOWEVER at light loads and low temperatures and especially at idling we need hotter plugs to avoid premature plug fouling, which is why myself and the other gents recommend use of the hotter plugs.

Hotter NON resistor plugs, keeping the temperature over 180 degrees, and not running the carbs anymore richer then necesary can help reduce premature plug fouling which is a problem ESPECIALLY when using low energy Magneto ignitions.

Best wishes yall, great discussion going.

John T

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Pete/ME

03-15-2006 02:44:13




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 Re: Spark Plug Cross Referencing in reply to John T, 03-13-2006 19:11:45  
A wealth of information from guys who know their crackers, but here I am (a carpenter) who's got a 215xxx that I broke down, unstuck, cleaned up, painted and just want to do a little roadside mowing...what plug and wires would be O.K.?



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Mike M

03-15-2006 10:01:20




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 Re: Spark Plug Cross Referencing in reply to Pete/ME, 03-15-2006 02:44:13  
Any plugs will work ,but for sure stay away from the automotive wires with a carbon core. You want wire in your wires !



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P Browning

03-13-2006 18:37:21




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 Re: Spark Plug Cross Referencing in reply to ol' guy, 03-13-2006 15:08:59  
Kurt_JDB, you asked a very good question. Electronic (and electrical) devices that send energy from one point to another in the ignition system send it through a network that resists the transfer. And maximum energy transfer occurs only when there is a match between the sending end resistance and the receiving end resitance. In the electrical (and electronic) worlds we call this Impedence Matching. The magneto is an electomagnetic animal which makes use of an inductance (a coil) to develop the high-voltage spike needed to bring a spark to a selected cylinder at the right time.

Magnetos are a gem of engineering, but of engineering done years before there was a need for resistor plugs -- these really to "quiet" the environment for hi-fi sounds systems among other things. They also were developed within the frame of battery-based ignition systems, and now electronic ignition -- surely nothing like you would find on your pre-1947 two-cylinder John Deere!

So when you use a resistor plug in plug as an element in a system designed for a non-resistor plug, you place an added unknown into the total circuit. The output impedance is no longer a match to the impedance of the magneto, and when a mis-match occurs, some of the energy which was to have been transferred is reflected back into the magneto. Reflected energy can overheat the coil, and enough of such abuse will eventually begin to show up in degraded performance.

I write tonight for all to hear -- men like Duane Larson and Glen Schueler have devoted an untold amount of hours trying to bring to us the vey best recommendations in spark plugs and magnetos. These are specialists! Listen!

And Eli -- I hate to burst your bubble, but the sparkplug crossreference you refered me to is wrong. It shows Autolite 388 as a direct replacement for Champion D23. You can go directly to Autolite and it will tell you that their 388 is a RESISTOR plug. 'Sorry! Listen to the experts. (PatB)

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Mike M

03-13-2006 19:00:03




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 Re: Spark Plug Cross Referencing in reply to P Browning, 03-13-2006 18:37:21  
So you are saying Auotlite Co. doesn't hire any experts ? You are correct about the autolite book and web site both cross the D23 to the 388 and it also says they are resistor type. I have also been running these for years way before microsoft or the internet was formed and I just haven't had any problems. But then again I also have some with the "dreaded" Champion plugs in them and they run fine too ! Go figure ? I don't think it is the plug as much as the other stuff.

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Glen in TX

03-13-2006 21:43:51




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 Re: Spark Plug Cross Referencing in reply to Mike M, 03-13-2006 19:00:03  
Whoa nellie, I go to a fire meeting and come back and... lol.. Mike, Kurt, others, I know many are still going to run the 388, 386 and other resistor plugs and carbon core wires on a mag but it's just a no no. May get by with it for a few runs on a old tractor fine but still not good on a magneto coil. High fuel prices are putting a end to natural gas and propane irrigation, industrial and oil field engines here with magnetos but use to be thousands of them and more in this area and others. We got into coil warranty issues in the past with the makers of coils for most every mag brand out there and they recommended or stated we NOT warranty mag coils ran with resistor plugs and carbon core wires because the added resistance was hard on the points, condenser and coil life. When mag coils were no longer hand wound and they started making the coils on computerized machines and encasing them in plastic a whole batch of bad coils could get put out there and the warranty problems got worse too. In my opionion there are very few new mag coils made today that can even stand up to industrial 24/7 use and why many go with other means of power now also. With the poorer quality coils today running more resistance on them can just shorten the life. I've seen older coils on those industrial engines with the proper wires and plugs set right that would run and run until they just wore the spark plug electrodes off but that wasn't good for them either. Some coils use to run 10 years or more 24/7 only shut down for maintainance before replacement but the poor ones today are lucky to run 1 second or 3 years in industrial use. The manufacturers now may tell you different but they just want to sell you more new parts! As far as plug brand we have had some engines that seemed to like one brand over another while the same engine on another fuel type didn't like it. Also whether we like or not some of the foreign made spark plugs are really the cats meow for keeping a industrial engine running longer and are good quality. I'm not going to mention brands but we have used some of those and were able to clean and regap them and run until they were just worn out but remember we did that because some of those larger plugs cost more too.

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Duane Larson

03-13-2006 19:32:32




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 Re: Spark Plug Cross Referencing in reply to Mike M, 03-13-2006 19:00:03  
Mike,
I think it is a matter of optimization. A tractor with an engine properly broken in and in good shape can be less sensitive to individual components.

A tractor with an engine which is not in the best of shape may gain from a hot non-resistor plug, copper core wires, and if using a distributor system (or a gear-reduction mag) having the center electrode of the plug at negative voltage with respect to ground will at least have the plug/ignition system optimized.

And an ignition system like that can't hurt on any tractor.

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Eli

03-13-2006 18:09:25




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 Re: Spark Plug Cross Referencing in reply to ol' guy, 03-13-2006 15:08:59  
You guys might try this websight. I use it for the sparkplug referance table. If you bring up the sparkplug referance table then save it to your favorites you wont have to look at the sights awful wallpaper. Link



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stray dog

03-13-2006 16:51:03




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 Re: Spark Plug Cross Referencing in reply to ol' guy, 03-13-2006 15:08:59  
so glenn in tex,
what plug should i be running in my 1948 g with mag. have been running the autolite 388 with no apparent problem but maybe i am damaging something and don't know it yet. but thought i needed a hot plug. help!



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Glen in TX

03-13-2006 21:53:13




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 Re: Spark Plug Cross Referencing in reply to stray dog, 03-13-2006 16:51:03  
Try the 18mm ones I listed above. I listed them from Hot to Colder. Guys can run any kind they want but it's a parts warranty issue to me is why the non resistor plugs and metallic core wires are recommended with a mag. Most of these old tractors don't get worked enough for problems to show up till later but a mag in poor shape will tell you it don't want to push all that fire through that resistance and quit sooner on you. Battery distributor ignition is fine with resistor plugs but you will get longer life using the others.

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Duane Larson

03-13-2006 15:54:49




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 Re: Spark Plug Cross Referencing in reply to ol' guy, 03-13-2006 15:08:59  
ol' guy,
For modern spark plug interchange information the best reference is a Champion catalog. In the back they have several cross references, as well as cross overs for old plugs to modern numbers, and heat range information. The Autolite catalog also has information but the Champion catalog is more complete. The AC Delco catalog offers little info.

In general Champion offers a wider heat range of plugs than AC and Autolite.

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Glen in TX

03-13-2006 16:16:25




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 Re: Spark Plug Cross Referencing in reply to Duane Larson, 03-13-2006 15:54:49  
I posted this last Thursday:
These were recommended plugs for JD 2 cyld. gasoline tractors and crosses. LP tractors can use a colder plug if needed.

18MM non resistor spark plugs:

Champion D23 = AC C88L or Autolite 378
Champion D21 = AC C88 or Autolite 377
Champion D18Y extended tip = Autolite 3116
Champion D16 = AC C87 or Autolite 376 or Denso L14U
For gasoline stay with the hotter plugs and not the D16. Try Brillmans or some of the other vendors or NAPA local if you can't find them. Use the NON resistor type plugs listed above with a magneto and metallic core wire also. Autolite 388 and 386 are resistor type and NOT recommended for mag use although suppliers will tell you they cross to a D21 do NOT use them on a magneto! Info showing the 386 & 388 are suppressor (resistor) plugs can be found in downloadable charts at autolite.com

Non resistor 7/8-18 spark plugs:

Champion W18 = AC C77L or Autolite 3077 or Champion W89D

Champion W14 = Autolite 3076 & 3075

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Duane Larson

03-13-2006 18:15:14




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 Re: Spark Plug Cross Referencing in reply to Glen in TX, 03-13-2006 16:16:25  
Glen,
Oops - I didn't see your posting as I was gone. Useful list.



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Glen in TX

03-13-2006 21:04:11




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 Re: Spark Plug Cross Referencing in reply to Duane Larson, 03-13-2006 18:15:14  
I know Duane, it was kind of hid in another JD A post. We had several spark plug conversations while you guys were gone lol. I did finally find that several cross charts will cross the D21 to a 388 but it and 386 are resistor plugs in Autolite charts. Earlier I thought the Denso L14U would compare with D21 Champion but found more crosses it is comparable to D16 until I have some in hand to look at. Found some other Bosch plugs but too cross to a colder plug in AC and Champion catalogs although Bosch listed them for JDs. Another iffy cross unless you have them in hand to compare.

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Kurt_JDB

03-13-2006 17:43:39




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 Re: Spark Plug Cross Referencing in reply to Glen in TX, 03-13-2006 16:16:25  
Glen,

Can you explain to us what is the problem with resister plugs and a magneto? And what is a resister plug, anyway?

Kurt



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Glen in TX

03-13-2006 23:21:56




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 Re: Spark Plug Cross Referencing in reply to Kurt_JDB, 03-13-2006 17:43:39  
Ole guy is saying why did he ask this? lol. and radio people are going to hate me. lol.

For a mag John T covered the tech part of it very well above and I mentioned the parts life warranty issues.

Non resistor plugs may have a small sealed gap inside also but not as much and plug core construction will differ having a solid metallic core or laminated metallic cores with little resistance. Aircraft, military and industrial magneto ignitions have used non resistor "shielded" spark plugs and wires for years to control RFI, Radio Freqency Interference also. Some of those shielded type spark plugs are take apart type allowing for a replaceable resistor core to be installed for some pulse type ignitions and solid cores for magnetos as well. Older cars had lots of metal surrounding the engines and that would suppress some of the RFI but later lighter made vehicles and higher voltage pulse ignitions and composite body constructions don't suppress the RFI well.

Early resistor plugs used a carbon type core inside the plug between the metal rod cores to suppress the ignition noise with radios. RFI, Radio Frequency Interference, the tac,tac,tac you hear on radio speakers around a non resistor type ignition source is what the resistor or RFI suppressor type spark plug was made to control. Also later on RFI control was built into spark plug wire cables and some distributor rotors as well. Later resistor type plugs use a sealed controlled gap or gaps inside and different type metal cores and even composite materials to control the RFI. As many different designs of RFI suppressor plugs out there as brands. Other layered metal cores were used in the electrode part of the spark plug to also give longer electrode life to the plug. Most modern resistor plugs can not have the resistance measured properly with a common low voltage ohmmeter and it takes a high voltage pulse (1Kv) to first be applied to eliminate contact resistance and false high readings.

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Kurt_JDB

03-14-2006 04:31:43




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 Re: Spark Plug Cross Referencing in reply to Glen in TX, 03-13-2006 23:21:56  
Thanks for the info Glen.

How "bout the rotor in a Wico magneto? Doesn"t this have a carbon contact that would act like the resistor carbon in a plug? Any problems here?

Kurt

PS Hope the fires stay out of your neck of Texas.



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Glen in TX

03-14-2006 10:01:00




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 Re: Spark Plug Cross Referencing in reply to Kurt_JDB, 03-14-2006 04:31:43  
Dist. carbons are small and more dense material and hurt more by not being there and too much arcing which makes the coil work harder and heat more. Any excess heating will kill the coils breaking down the insulation inside between the windings.

The fires were 150+ miles from here E NE of Amarillo but we are still dry for the potential of the same disaster.



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