The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: suecanada on April 20, 2011, 09:26:49 AM
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I asked John Rayski of Euromotoelectrics about the resistance type WR 5 DC sparkplug for my R65LS. I had just finished reading Snowbum's tech article that said not to use them. Here is what John Rayski replied:
Sue,
The use “WR” type resistor spark plugs in a BMW R Airhead vehicle application are of no-consequence in regards to performance, coil incompatibility, component longevity .
I asked this question about 5 years ago, when Bosch USA discontinued the availability of the non resistor W5, W6, W7DC.
The amount of resistance is inconsequential .
Period.
I previously worked for Bosch USA and my old engineering colleagues do not understand what all the issues are that the Airhead community is concerned about…
In the meantime, we sell hundreds / per month of each resistor plug #....
Oh well, old habits …
Thx for asking and hope that helps…
Best Regards,
J o h n R a y s k i
Euro MotoElectrics
Be interesting to ask Rick Jones of Motorrad Electriks. Both of these gentlemen's knowledge of electrical issues I trust highly. Both offer a highly recommended upgrade to our airheads alternator output and other fine products and offer fine customer service!
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The Resistor Plug debate is a bit like an oil thread...everyone has an opinion. I'd have been happier if "The amount of resistance is inconsequential" had been qualified as applying to electronic ignition bikes where for the most part it is probably true.
For a points set up I'm still inclined to trust Snowbum who strikes me as being a very smart guy with in depth knowledge of electrics/electronics besides being a very experienced Airhead mechanic.
I'm also inclined to trust this guy who set out to test the theory himself. http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1257432246/14#14
I believe the debate will continue.
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I inadvertantly used resistor type spark plugs in my '81 R65, never had a problem with them .
I was using Bosch Platinum plugs, the plugs didn't seem to like the 'wasted spark' ignition system too much .
The center electrode is a fine wire and none of it extends past the ceramic insulator .
After about 8,000 miles (13,000 km) of usage, the center electrode was eroded to about . 080 inches (2mm) below the surface of the center insulator, so I had an effective spark plug gap of about .110 inches (2.8 mm), when it should be around .028 inches (.7mm) .
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The way it was explained to me is that you basically have a series circuit comprising the coil secondary, spark plug cap resistance, spark plug resistance, and spark plug gap. Since the plug gap is basically infinite resistance any resistance offered by the spark plug is irrelevant.
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Since the plug gap is basically infinite resistance any resistance offered by the spark plug is irrelevant.
Yes - until the arc is struck then the resistance across the plug gap falls dramatically to the point where excessive resistance in the plug circuit will have some effect as some energy will be dissipated in the resistor reducing the energy that would otherwise be dissipated in the spark. It can't be otherwise. It's simple ohms law. Well maybe it's not simple but it's still a fact.
The link I posted demonstrates that if you go on adding resistance the spark eventually gets weak enough not to fire a plug in less than perfect conditions.
Now the real question is whether this reduction in spark energy has any practical effect on engine running. For most people there may be no practical consequences as a good electronic ignition system has so much excess energy available that it can afford to lose a small amount across the resistor.
A points ignition system may not be able to always afford the reduction in spark energy in all circumstances because it only has half as much as the electronic ignition to start with (or more probably less than half because of less efficient switching).
BMW designed the points ignition to have 1000 ohms in the plug circuit. 1000 ohm plug caps are very hard if not impossible to find these days so many people are having to run with a 5000 ohms plug cap and this doesn't seem to cause a problem. Adding another 10,000 ohms with a resistor plug is just asking for trouble though.
I need a lot of convincing that 15 times more resistance than BMW intended is not in some marginal circumstances going to provide me with a weaker spark than the engine requires.
And "The amount of resistance is inconsequential" is too much of a generalisation to convince me even if it did originally come from a BMW source.
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Can't we just go back to the spline lube question? [smiley=ROTFLMAO.gif]
And what about that oil thread, and the tire thread, and that loose thread on my underwear...
Monte
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I didn't seem to have a problem with the Bosch platinum plugs that Bob had in my 1988 R100RT ? But, my wife considers me a very resistant guy!
Practically speaking, there is generally plenty of voltage to overcome a paltry extra 5K or 10K ohms of resistance in the secondary coil circuit, especially with the fast switching edges of the transistorized ignition circuit. The extra resistance will reduce available energy at the spark gap slightly, so indeed in fairly marginal situations the extra resistance could make a difference between JUST being able to start and not starting at all. I would also assume that the spark plug itself will run a bit hotter as the plug cap (if a resistor cap) will be dissipating heat from its internal resistor as will the plug with its insulator-shrouded resistor, so the plug/cap combination will be warmer. Enough to have an adverse effect on the life of the plug, I don't know, but not likely unless you expect to get 8 years of usage our of your spark plugs.
I could see where the lower-powered points ignition setup would be more likely to be adversely affected, but still not likely to the point of causing major system failure.
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Can't we just go back to the spline lube question? Smiley
And what about that oil thread, and the tire thread, and that loose thread on my underwear...
Sorry Monte
You know I can't resist !