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Spark plug info for dual spark RT


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Yesterday I put in Denso Iridium plugs I had bought for my RT, before doing the valve adjustment and throttle body sync. The IK22 primary plugs had been easy to find, but it had taken some research (through clubplug.net) to find the iridium cross reference for the secondary plug. I used IXU24's for the secondaries. Since the factory BMW manual predates the dual-spark model, it doesn't show the torque for the secondary plugs, which are 12mm thread instead of 14mm. I found some generic torque specs on sparkplugs.com showing that 12mm plugs get about 2/3 the torque of 14mm plugs in aluminum heads. So I used 25 Nm for the primaries and 16 Nm for the secondaries. I also looked up the Denso specified gaps for both plugs, which is .032" for the IK22 and .035" for the IXU24. They are factory gapped, come with plastic sleeves to protect the electrodes, and when I checked mine they were pretty darn close to spec.


The bike runs fine with the new plugs, but I can't say I notice any real difference, other than the incremental smoothness it picked up due to the re-syncing of the throttles.

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Bosch had a standard procedure for installing plugs, if i recall properly, 12mm plugs with a flat type washer are to be torqued from 11-18 ftlbs in an aluminium head.



what kind of life are the iridium plugs suppose to provide?



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The sparkplugs.com site has info stating that in a standard automobile engine they should last 40K-60K miles. But they are probably "working harder" in an oilhead; certainly the higher compression ratio would have an effect. I'll be happy to report my findings when I check them every 6000 miles! smile.gif

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  • 10 months later...

Better late than never.


I checked my Denso plugs (top and bottom) at the 18,000 mile service and all four looked nice and clean and light gray/tan in color. Essentially no deposits, absolutely no hint of oil or soot. The stock secondaries had been getting sooty and oily and I believe fouled at some point. The engine had been burning very little oil, so I don't think the change in plug performance is related to engine break-in. FWIW, I'm happy with the Densos and will be sticking with them.

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  • 1 month later...

Progress report on Denso Iridium plugs for dual plug RT:


I checked them again at the 26,000 mile service and they still look great and run great. Negligible electrode erosion (really only visible on the ground electrode; the pointed center electrode doesn't seem to wear) and a nice light tan color all around.


These plugs have now been running about 18,000 miles so far. I'll probably replace them at the 30K service just for good measure.

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