Resistor spark plug converted into a non-resistor spark plug (with pictures)
 

Well I have done it. I have converted resistor spark plugs to non-resistor plugs. I did this because non-resistor plugs are so hard to come across despite what anyone on here says, you can not walk into any local autozone and buy non-resistor plugs without either going to the dealership or ordering them online. The plugs that I have are Champion RS12YC #401. The recommended plug is S12YC, no R. These plugs are only $2.09 at autozone and they almost always have them in stock.

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Using my multimeter I set the dial for resistance and short the 2 leads together to get a 0 resistance.

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Next I connected the leads to either end of the spark plug, I'm not sure what the resistance is supposed to be, but the multimeter dial is set at 200k and the plug is showing 22.3 resistance. I guess if I moved the dial to 2000k It would be 223 resistance. This may not be the exact resistance of the plug because its kind of hard to take the pictures and hold the leads in place to get a solid connection. Either way the resistance is there.
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Next take the spark plug and unscrew the cap. This step you need to be careful as the tip seems to be threaded into the porcelain with thread lock. Use visegrips to get a firm grip on the tip and a regular crescent wrence on the body.
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If you look down into the plug with the tip out you can see that it is hollowed out.
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Next empty the contents of the spark plug which will be a smal cylinder-shaped piece about <1 cm and a small spring. the cylinder-shaped piece is the resistor.
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Next I take the resistor (just to make sure it actually is the resistor and I test it against my multimeter.
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Now this is the part that varies, I was originally going to use a 10 gauge unsheathed wire cut the length of the resistor, but then I wanted something solid so I grabbed a coat hanger. After realizing the coat hanger was not made of copper, I decided to grab my old Bosch H9DC plugs and crack them open and cut out the copper core. I guess you can use any type of metal that carries a current, especially since there is a spring in the plug that is probably just steel or some alloy, but since this is new to me, I chose to play it safe.
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Finally put everything back together, minus the resistor and then hook the plug up to the multimeter leads and you should now have a non-resistor plug :D. *Note that the spring goes in first and then the legnth of copper. Another variable of this is to bypass the spring and just use a length of copper that will reach the plug's bottom, but not be too long on the top.
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.....The dealer sells the right plugs....you can find them online too....

I'm going to make some,and see if my 1/4 mile times improve at the track.I run triple grounds for my nitrous,can't have fouling plugs.

True, but the point is to not have to order online and wait for 3+ days just to get spark plugs and that goes for the dealer as well. Sometimes they need to order non-resistor plugs and the price per plug was something like $ 7.68. So why hassle when you can just go to pretty much any local parts store and buy some resistor plugs and make your own? Actually, making your own costs less and takes less time than going to the dealer or ordering online. I'm fortunate to live 5 mins from the dealer, but not many other members have that accessibility. So this is something to help out those that want the convenience and cost-effectiveness of making their own non-resistor plugs. By the way, I did notice a much smoother performance once I took out those resistor plugs I previously installed. My remote start would take 3-4 tries to crank the engine, now its just one....maybe 2 if the engine is cold and sat overnight.

Cool info. Glad it worked out for you.

Not that I am against these sorts of modifications, I think I've just become lazy. Last time I ordered spark plugs for my 190E I bought 12. I think the change interval is what 16K? I buy nearly all of my parts online as it is anyway.

It is good to have an alternative though. I actually was able to buy the proper non-resistor NGK's for my 420SEL at the AutoZone last summer.

ismalley:

Re: meter readings

Inasmuch as you were using scales for Kohms (thousands of ohms), the numbers displayed on the meter represent that number of thousands of ohms, i.e., 22,300 ohms,and 139,000 ohms! Those figures are way above the actual resistance of 4700-5000 ohms which is typical of spark plug internal resistance. Technique counts.

After you converted to a "non-resistor" configuration, you should have used the 200 ohm scale to more properly gauge the result of your efforts.

I didn't really look into the measurements of the plugs prior, I was just concerned that there was some resistance in then and that after the modification that resistance would be gone. I did toggle between 200 & 2000, but the overall goal was to get zero resistance in the spark plug itself. The showed zero resistance after the modification. I don't know whether 200 or 2000 matter, but I'm assuming since the plug is now a non-resistor plug, it should not matter what the dial is set to as the values should still show zero. I still have some Bosch HRDC0 plugs, I can test those with the different scale values of my multimeter. What should the values be of the resistance of those plugs?

Not sure why you would go through this effort as the non resistor plugs are still available. May cost a few dollars but you are assured of quality.

The fallacy in your modification is that you may read 0 ohms using the less then 9VDC provided by the multimeter.
you can use any type of metal, but all metals are not equally conductive.
Copper is the most common in non resistor plugs as the NGK BP5EFS, but the best conductor would be silver as in the hard to find Beru/Nology S1K Silverstone plugs

Impress a service voltage of 35KV + and you may find even the slightest gap between conductors can create an internal arc which will degrade the plug.

You can't compare a solid top to bottom electrode with the pieced together electrode you are creating.

Ed A.

When I last needed plugs I too was able to source NGK non resistor's for my 420sel without a problem, only a few dollars each at O'reilley's.

This is a good point, I did not think about the degrading of the plug internally, but wouldn't also apply to the resistor as well? It is not a solid conductor and it too would be able to have a gap in between. On another note, the plug does have an internal spring which would make sure that there remains a solid connection between the conductors. I will pull the plugs in a few months to check the integrity of the components. Also, I do not understand what you mean about the fallacy in the modification using < 9VDC.

I have tried oreilly's, as a matter of fact I was on the phone with them today and they said they do not stock them, nor does pep boys, nor does autozone. They all cross referenced to a resistor. My location is Palm Springs and there are plenty of older and newer model MBs on the road. When I go to the junk yard I usually make it a habit to go and pull one of the plugs in the MBs there and I have yet to pull one where there was a non-resistor plug in it.

You would be surprised at the effect of contact area. Your copper replacement slugs might not be as smooth as the resistor's contact area. or maybe it its better, I'm not sure.

The voltage that passes through that area, normally, is between 20 and 30 kV, with a 5K resistor that's about 4+ amps of current. With the 9V that the volt meter can supply you only get 0.18mA. A fraction of how much current will actually flow through there. That will have an effect on your measurement to some degree.

To be honest, I've not been able to buy the plugs for my m103's locally. I have been able to buy the plugs for the m116/m117 locally.

I was just checking around and found NGK BP5ES-11 plugs at Advance Auto. It says they are nickel and no resistor. Nickel is a good conductor. Would they be a good replacment for the copper core plugs?

Paul

Some useful info from NGK:
http://www.ngksparkplugs.com/docs/tech/design_symbols_plugs.pdf

I see no mention of nickel core. All the websites I looked at said copper core.
NGK 7732 BP5ES-11 Nickel Spark Plug

Ok, the -11 means it is designed for a wider gap. I just sent the question to NGK to find out about the nickel core vs the copper core. I'll let you know what I find out.

Paul

Thanks much for this resarch/write up. I've found the denso plugs for cheap at one place online, but in general availability seems low and prices high.

Is that old grey looking slug that you pulled out of the resistor plug made from a material that provides resistance and the copper you put in it's place is done to deliver no resistance?

I wonder if you could just fill the cavity with silver solder?
We are having difficulty finding the non resistance plugs here for a sane price...also have driven to the city only to find out that the parts guys computer tells him he stocks the ngk bp5es for the 420sel, but then he comes from the stock shelf holding bpR5es. The R stands for resistance plug. Strangely the computer also tells him the bpR5es plugs are 4.99 for a package of 2.....but the package he brings me is a molded plastic case with 2 spots but only one plug in the package....guess they are 4.99 for each plug...with a bonus invisible plug.

I would not use solder because I'm not sure about the heat tolerance. I would only stick with w$ in the original core. There is a reason they chose copper. Also, there is a small spring inside the plug as well I left that in ensure maximum contact. What I did was just crack open a Bosch plug and cut the core to the proper length. On a side note, I have have recently switched back to the RS12YC plugs as there is no documented facts that it causes any adverse effects tho the ignition system. 2 separate.independent mb mechanics confirmed this for me and neither of them has heard of mb publishing anything regarding the use of resistor plugs. I did not put the resistors back in I just got new set. Good luck

Back to non-resistor plugs.
 

Ok so after leaving the last set of resistor plugs RS12YC in the car, I did not have any issues with driving it for 40,000+ miles. Went in a few days ago and bought another set, but I was still curious about the non-resistor conversion and so I went to a hardware store and purchased a foot of solid copper rod the same diameter or extremely close as the internal resistor of the plug and I cut it down to the same length. Anyways, converted the plugs to non-resistor plugs with the solid copper rods and drove around with them for about a week now. I can't say if its because the other plugs had about 40k+ mile on them or if its because these have no resistance to them, but there is a definite noticeable difference in the smoothness of the driving, especially the acceleration. I also notice that when I'm on the freeway doing 70 mph it feels like I'm going slower.....or rather like I'm not putting a lot of effort in to keep speed. Hard to explain. Before it was like I had my foot on the gas quite hard just to maintain 70 mph and the engine even sounded like it was revving harder, but now its so smooth and effortless. Funny thing is, the car didn't hesitate with the resistor plugs and it always started right up and idled smoothly So I didn't notice the difference until after putting this last set of non-resistor plugs in. From now on I will just do this conversion to keep using non-resistor plugs, plus the RS12YC are only about $2 vs H9DC0 at the dealer which run for about $7-$8. A foot of the copper I got, which actually has 3 solid copper rods (1 white sheathed, 1 black sheathed, and 1 bare rod) was only .90 cents. Several members have stated that the non-resistor plugs are readily available online, but to this day I have yet to find any readily available which are direct replacements for the m103. I have seen most manufacturere numbers contain a "R" somewhere in the part number which denotes that the plug qis a resistor type plug.