BMW R1200R R1150R/T F800 K1200R R1100R/T R1250R RnineT Message Board

I bought a pair of Autolite XS-3923 Platinum Spark Plugs.
Manual states .031" Gap - Autolite states .025" Gap - Stock NGK's were .020".
Thoughts?

The 0.031" (which manual?) is surely wrong. 20-25 thou is the norm. The NGK BKR7EKC I use have multiple non adjustable gaps and are correct out of the box for my single plug per cylinder model.

Page 12 and 83 https://www.dropbox.com/s/1e1ov95vm2ssl ... l.pdf?dl=0

"4. If installing new plugs (every 12K miles), check that they are still set at the factory set gap of .031 in (0.8mm)."

Or look at service data in https://www.dropbox.com/s/8cb55xst44iw3 ... S.pdf?dl=0

"Spark plugs
Electrode gap 0.8 (0.0315) mm (in)
Wear limit 1.0 (0.039) mm (in)"

I apologise . The NGK BKR7EKC are indeed specified at a gap of 0.03" and 0.8mm in my paper owners manual. Maybe because it is a multigap type plug? I don't know the design of the plugs mentioned in your first message.

Oilhead maintenance manual by Carl Kulow and others.
https://www.dropbox.com/s/1e1ov95vm2ssl ... l.pdf?dl=0

The piece about spark plugs was written by Rob Lentini.
Page 83 "I took the dive, bought Autolite 3923s, set the gap to the BMW specification of .031” or .8mm, and went for a ride. They worked great!"
Page 84 "So here are your options, gapped at .031” or .8mm:
OEM:
Bosch FR5DTC (3-electrode)
Bosch FR6DDC (2-electrode)
Non-EOM:
Autolite 3923 (1-electrode)
Champion RC9YC or RC9YC4 (1-electrode)
(Note: If you are hard-core Bosch, their 1-electrode Autolite 3923 equivalent is the F6DC)"

Is there a list of suitable spark plugs for our bike?
That 3 electrode Bosch FR5DTC is cheaper than the standard 2 electrode NGK, in the UK anyway.

I replaced the factory installed Autolite plugs on my '02 R1150r at 15,000 miles, 24,000 km .
Installed the same Autolite plugs then .
I put 45,000 miles,73,000 km on that set of plugs .
Part of the annual registration process required an exhaust emissions test, I did the last test on these old plugs and the exhaust gases, was at 5% of the legal maximum .
A national auto parts store here in the US, O'Reilly's, had platinum spark plugs on sale at that time, can't remember if they were Autolite or Bosch, put those in and saw no change in engine operation, or fuel comsumption .
I don't think it really matters in the long run, what plugs you use .
I experimented with my airhead bikes and Guzzi, the multiple ground electrode, platinum, iridium, etc .. plugs, nothing really produced any additional benefit .
I also think the 12,000 mile, 19,000 km recommended replacement, isn't warranted .
To get back the subject of this thread, I use .031 in. gap, I think that's around .78 mm .

My service record shows I have changed my plugs approximately every 6000 miles (3 years or so, yes I'm a low mileage fair weather rider). Getting the plugs out and cleaning the head casting of grit, bitumen and flies is such a faff that I put in new plugs each time. £16 for two plugs seems a bit expensive and may try Green Plugs next time.

The premise behind iridium plugs is less wear of the electrode hence more consistent performance.
Also lower resistance, creating less heat in the Plug.
I mainly like them because they last far longer than any other types.
Less maintenance = more riding!
Thanks for all the feedback, I will gap them to .031".
Now to finish installing new fork seals.....

I installed a pair of these some years ago and one of them blew the iridium pellet off its tip and disabled the ignition system. I don't know where that little pellet went but I hope it is softer than an aluminum piston!

I sure hope it went down the exhaust.

I can't measure my plug gap with feeler gauges.
The gaps are curved and are not effectively adjustable.
Looking up plug equivalents reveals that the oem NGK I use are not equivalent to the other plugs quoted above. Maybe European fuel does have different ignition and combustion requirements?

The NGK dual electrode plugs I pulled out were at .020"and less.
The gap varied from one electrode to the other on each plug.

gregor wrote:I can't measure my plug gap with feeler gauges.
The gaps are curved and are not effectively adjustable.
Looking up plug equivalents reveals that the oem NGK I use are not equivalent to the other plugs quoted above. Maybe European fuel does have different ignition and combustion requirements?

You have to use wire gauges, they are common here in the us auto parts stores. Also stainless safety wire comes in .20 .25 and .32 here in the states.
The octane system for rating is different for sure. I have always ran the cheapest (lowest octane) here in the us in my 1150 w/ no problems. I generally just install the plugs (usually NGK) out of the box with just a quick look to make sure the gap is some what close. The modern ign systems will fire anything that has some gap..Ha! The manufacturers gap their plugs at the factory to what they think and have tested to be correct for that plug.

Having said that , here in CA (states) the fuel is formulated different from the rest of the country and I'm not sure what they do in Europe/UK but that should have no measurable effect on the engine.

I will get around 16K to 18K between changes. They would probably go much longer but it seems once a year works for me.(I except what ever mileage I have on the annual change). I get mid 40s' or higher for fuel mileage.

Never seen or used a wire gauge, I know of them in principle. But adjusting a side electrode plug may be tricky. NGK work fine out of the box and old ones look a nice even grey colour. When we had leaded fuel they were fawn if running ok.