Spark plug resistance
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Road Warrior
Joined: Jun 2015
Posts: 1,325
Likes: 140
From: Edinburgh UK
Spark plug resistance
now don't all groan at once 
I've was chasing what looked like a bit too much knock on the front cylinder a couple of months back so I replaced the plugs and it went away ...for a while, it's come back.
I checked the spark leads, the front one is on the upper limit according to the service book (12.5K ohm) so I have one on order. Rear is slap bang in the middle of spec.
Thing is, I was looking at the plugs ...the old ones (original) measured 7K and 9K but the two new ones I put in still look like new but only measure 140 ohm
Original ones were 6R12, but the new ones, from the dealer, are marked 6R12* with a dot on the end
From what I read they should be around 4-6 K should they not? Do you think these are duff or wrong ones or something?
cheers
I've was chasing what looked like a bit too much knock on the front cylinder a couple of months back so I replaced the plugs and it went away ...for a while, it's come back.
I checked the spark leads, the front one is on the upper limit according to the service book (12.5K ohm) so I have one on order. Rear is slap bang in the middle of spec.
Thing is, I was looking at the plugs ...the old ones (original) measured 7K and 9K but the two new ones I put in still look like new but only measure 140 ohm
Original ones were 6R12, but the new ones, from the dealer, are marked 6R12* with a dot on the end
From what I read they should be around 4-6 K should they not? Do you think these are duff or wrong ones or something?
cheers
Plug resistance
just out of curiosity what year is the bike. Early Delhi cals had some that had the parameters too tight and git a lot of false knock. It was very evident in some stock and tuner cals.
Cruiser
Joined: Nov 2005
Posts: 163
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From: Wherever I put my helmet
From what I understand, you cannot check Champion made spark plugs made with the SAC9 resistors with a multimeter. Takes a high voltage setup to check them. That is why they came out with a style using FISS resistors, like NGK. So that mechs can check em. That said, seems that aircraft have been having issues of late with Champion made plugs.
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Road Warrior
Joined: Jun 2015
Posts: 1,325
Likes: 140
From: Edinburgh UK
Why is nothing ever simple 
So if champion say that FISS type plugs have black coloured terminal ends, should we presume that our plugs are SAC09? and can not be reliably measured with a low voltage DVM?
Ref: http://www.motospecs.com.au/assets/f...Difference.pdf
I just found it funny that the two old ones read 7 or 8K but the new ones only 140 ohm and wondered if it meant anything.
Maybe HD are getting a slightly different spec of plug these days??
Can we presume that if the two seem to read the same then they are probably fine?
I did swop the front and rear over when I put them back in and got negligible knock today on the same run as yesterday ...go figure ??!?
So if champion say that FISS type plugs have black coloured terminal ends, should we presume that our plugs are SAC09? and can not be reliably measured with a low voltage DVM?
Ref: http://www.motospecs.com.au/assets/f...Difference.pdf
I just found it funny that the two old ones read 7 or 8K but the new ones only 140 ohm and wondered if it meant anything.
Maybe HD are getting a slightly different spec of plug these days??
Can we presume that if the two seem to read the same then they are probably fine?
I did swop the front and rear over when I put them back in and got negligible knock today on the same run as yesterday ...go figure ??!?
Cruiser
Joined: Nov 2005
Posts: 163
Likes: 10
From: Wherever I put my helmet
Hard to say but I suspect that the HD Branded Champion plugs are indeed SAC9's. And I think maybe Champion's quality control has slipped and they got called out on it by the Aviation community. The sucky part is there is really no way for us to test the plugs without a high voltage plug tester and the only thing we will see there is the spark, not a measurement of the resistor which takes more specialized equipment. And you know HD as well as Champion are going to run their supply of older plugs out regardless. So we are left with the chuck it and try a new set method which is wasteful. The only difference between a Champion RA6HC and a Harley 6R12 is the nut at the top. One is removable while the other is not. As far as I know, Champion does not make a FISS type plug for HD's. But, NGK does. A NGK DCPR7E is what you hear most using. I am going to try a set of NGK DCPR7E-N-10. They both the same plug but the latter one has the non removable nut. Of course a pair of pliers could easily convert the removable nut to a non removable nut. The other difference I noted in the specs is that the DCPR7E has a 0.031 factory gapping while the DCPR7E-N-10 comes 0.039, which is another reason I am choosing the DCPR7E-N-10 to try as it is closer to the middle of the factory gap range. I think it sucks that those little difference doubles the price of the plug tho. And of course I also check the gapping and reset it if need be. I don't buy into that you don't have to gap it crap when it comes to standard style plugs.
Last edited by Tsani; Oct 9, 2016 at 02:32 PM.
Cruiser
Joined: Nov 2005
Posts: 163
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From: Wherever I put my helmet
Received the NGK DCPR7E-N-10 plugs today. They were gapped at 0.039 which I adjusted to 0.040. They ohmed out 4.62 and 4.67 on my calibrated fluke DVM. I will try them out this weekend on a 140 mile ride. Packaged nicely too. The gapped end of the plug was protected by a sturdy cardboard tube in addition to being boxed. Nice. I paid 22 dollars for 6.
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Road Warrior
Joined: Jun 2015
Posts: 1,325
Likes: 140
From: Edinburgh UK
My slight knock came back during a proper run so these are going in the bin me thinks. My DVM is a cheaper no name unit but the old ones read 9k so 140 ohm just sounds faulty.
It would be nice to hear if the NGK play ok with the ion sensing if you could let us know?
It would be nice to hear if the NGK play ok with the ion sensing if you could let us know?
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Cruiser
Joined: Nov 2005
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From: Wherever I put my helmet
Yeah No problem. I want to know too. and right now I am having no false events or real. So it will be easy to see if I have one. I data log almost continuously. Just too easy to keep the little blue box hooked up.
