Went to the dealers today and had a look at their plugs

Whole new box and they are marked 6r12* with that dot on the end, only ones they have - they measured a steady 140 ohm on my crappy dvm

They also had some 6r12G (the pretty gold ones) - they measured 20,000 rising to 60k ...so there is some capacitance in those ones?

I wonder if they have changed supplier or we get different over here in the UK? or if infect the ion sensing actually cares at all??

Anyway, the replacement front spark lead is half the resistance of my orig one and well within spec so I'll see if that reduces my tendency to log knock

 

Initial impression:
My bike likes these plugs. Idle is better, smoother.
I may need to adjust the timing a bit, or check the AFR. A little pop but that could simply be the cooler weather. Getting ready to down load the logs, so we will see.
The HD plugs I pulled out were 6R12's, no *. Three thousand miles on them. rear looked a little lean.

 

Two hours of logging show no false retards.
I think I am going to like these plugs.
After tomorrow, I will pull em and see how they look.

 

Without proper high voltage spark plug resistance checking equipment measuring with a DVM, as Tsani mentioned earlier, is simply not reliable.
While QC is always in question all we can rely upon is the stock plugs to be our best guess without knowingly introducing another variable into the ion sensing mix.
Bob

 

225 miles today on the NGK plugs. From 0 to 100, some good high rpm down shifys, no issues at all. Not a burp. I would have no problem running these and they can be checked with a DVM. It's good to know I have a good go to plug besides the OEM plug. Champion makes the OEM plugs but has come under fire in the aviation community where reliability is a must.

I have a 1000v Meg ohm meter. I will see if that gives me a reading on the OEM plugs. Problem would be the scale. Really not fine enough down low.

But for now, I am going to run the NGKs. My bike like them. YMMV.

 

If you drive it hard enough and load up the cylinder with hard throttle, you simply need Harley's plug. I can get away since I ride easy with an NGK but the resistance is way off from Harley's bike plug. The compression affects the resistance value and the ignition reads it. This is Harleys ping sensor, at least on the older bikes like mine. Make sure your gas is mid grade or higher and use a Harley Plug.

 

With my dvm the old two that came out were a steady repeatable 9K and 7.5K.

The new ones are a steady and repeatable 140 ohm, as are another couple of samples at the dealer.

I only know how to compare like with like ?? which was why I raised the question

Incidentally, the service manual quotes the resistance spec for the spark leads, but not the plugs themselves? I don't really want to get into a discussion about how ion-sensing works and Harley's 3 patents on the subject (apparently), that has been done to death elsewhere - I was just wondering what others read for resistance across their ohm plugs

 

I understand how the sensing works and I am ok with the NGK plugs doing the job. But that's me as I have said, YMMV. It's not just the plugs you need to be concerned about, the wires and the ignition module all play into it as well. There are other factors too and once you go from the stock platform, you are changing the parameters of the circuit design. This includes ECM calibration, compression, cams, plug gap setting and timing as well. And I am well beyond that. Your not going to be able to read it with a DVM or at least with the average DVM.

 

When I get a bike in that has false knock issues changing to a std 6r12 plus usually eliminates the issue.
For higher compression builds I find reducing the gap will help false knock.
As long as you don't care about false knock virtually any plug that fits will run the engine. You may never know or realize differences in performance while riding down the road. Fuel mileage will vary with false knock events that end up as long term timing changes.
I try to eliminate as many variables as possible when tuning these engines.
Now that the M8 uses a normal knock sensor (sensor bolted to engine) false knock may not be as prevelent when tuning. Time will tell.
Bob

 

yup. Time will tell.