Lower plug on dual plugged '04 GS

[PETDOC]

I was doing a tune up on my '04 1150 GS and have noticed that everytime I change the plugs (every 10,000 miles), the center plug looks great (NGK BKR7EKC) while the lower plug (Bosch YR6LDE) looks like it is slightly fouled (ie, little dark). These are the plugs that came on my bike and the bike runs great so I'm not inclined to change anything, but I was wondering if a slightly hotter lower plug would be indicated. I have seen someone make reference to the fact (?) that on the '04s the lower plug is only there for enhanced low rpm combustion. In essence it is there for EPA compliance, and does not function as a true dual plug set-up--hence, will always appear a little fouled. Does anyone know if this is true?

[MrB]

IIRC, that is not uncommon and not really an issue. I had the same bike and my lower plugs were a little darker than the main plugs.

You'd get more responses over at the GSPot forum on ADVrider.com

[cjack]

Must run cooler. Wonder if it needs the next up heat range. I wouldn't experiment, one would think BMW has it figured out.

[rinty]

Doc:

There was a great article on this in the MOA News a few years ago. The situation is that on the boxers there has never been optimal combustion at the periphery of the combustion chamber i.e. in the area just above the outer top edge of the piston, all the way around. For '04 BMW placed a second plug in that area, the better to complete the combustion. The end result is cleaner burning, one more horsepower, and reduced surging.

In his book, "The Gold Plated Porsche", former Car and Driver editor Stephan Wilkinson states that hemispherical combustion chambers are not the best ones for optimal combustion efficiency, as this was an issue for Porsche in its earlier boxer engines as well.

Rinty

[feds27]

....I have seen someone make reference to the fact (?) that on the '04s the lower plug is only there for enhanced low rpm combustion. In essence it is there for EPA compliance, and does not function as a true dual plug set-up--hence, will always appear a little fouled........

Yes, I posted that on the Pelican parts forum. When I did my last plug change, I brought the plugs with me to the dealer and asked the shop foreman about it. He recommended sticking with the BMW recommendations and then went on to explain how the plugs fire on the '04 dual sparks. The center plug fires all the time, the lower plug fires at RPMs lower than 2000 or something like that but only on the exhaust stroke.

I was using NGK for both center and lower plugs with great results. I used the same center plug as you and then the lower plug was a 8 range which is a colder plug that cross references to the BMW recommended Bosch. The good thing with NGK is that they have much smaller heat ranges so if you decide to step up the lower plug to a 7 range to match the main plug it probably wouldn't be a problem. I had tried a 7 as my lower plug and ran the bike for about 100 miles, the plug looked a bit better than the 6 but after I spoke with the dealer I decided to reinstall the 8 range. The odd thing is if you look up R1150R in NGK books, they show a 6 for the lower plug which is two heat ranges hotter than the 8 cross referenced from the BMW Bosch plug. For NGK a lower number means hotter, so the 6 is a hotter plug than the 8.

I also did some cross referencing on Autolites and looked up the R1150R in the Autolite books and I found a similar thing, the spark plug manufacturers seem to recommend a hotter plug for the lower.

If you have time check out the Autolite and NGK websites to find their recommendations based on the R1150 and also do some cross references from the BMW Bosch plug numbers on sparkplug.com. You'll find the numbers don't match.

[GlobalRider]

These are the plugs that came on my bike and the bike runs great so I'm not inclined to change anything.

Therefore don't.

Yes, those are the spec plugs and yes, the bottom one is a medium brown in color.