R1100RT Denso Iridium Spark Plugs

[tlangman4]

Oilheaders-

My 2000 R1100RT is currently in the shop getting some much needed updates from sitting too long in the previous owners garage. The complete tune up will include installing the Bosch EV14 injectors from EME. I will also be replacing the spark plugs and am considering the Denso Iridium plugs that are available for the R1100.

Has anyone used these plugs?

It appears the Autolite 3923 are a fairly popular replacement plug as well. Ultimately I am trying to eliminate the surge that was present in the bike during the short time I was able to ride it after purchase before the weather turned.

Thank you for any useful feedback!

TL

 

[robsryder]

I have a 94 R1100RS purchased new. I have never experienced this surging issue, but I do understand that it is a problem for some. Insofar as spark plugs go, I've used the Bosch ones. Initially these had three grounds, in the past few decades there were two grounds.

On the IBMWR website there are a number of tech tips; in the section for oilheads some of these tips specifically address the surging issue -

R1100 Surging Fixes - The Internet BMW Riders

R1100 fuel injection/surging/fixes by Rob Lentini Part 1 of a 4 part series: My original four part article was originally posted to the IBMWR tech…

ibmwr.org

Oilhead R-Bike Tech Articles - The Internet BMW Riders

Technical Articles for Type R259 R850, R1100, R1150, R1200 BMWs Disclaimer: All material contained herein retains the original author’s copyright. The material presented here is…

ibmwr.org

[NOTE: edit made for technical correctness - the electrode is the centermost part, of these there is only one. the outer part, where there can be multiple, are grounds. - newer bosch plugs have but a single ground. See Paul Glaves comment below regarding "indexing" the ground away from intake valves so that fuel / air mixture more quickly "sees" the spark for ignition.]

 

[GTRider]

Based upon my experience with my ‘95 R1100RSL, I’d recommend the inexpensive 3923 plugs over the $pendy iridiums and replace them at every 6k service. I remain somewhat leery of the 0=0 adjustment routine, especially with different injectors on the bike, and suggest riding the bike with the new injectors after a thorough setting to baseline (esp. valves) before getting into deeper mods.

The surging issue on pre-twinspark 1100s was reported mostly at steady-speed riding at lower rpm with light throttle. Many riders never experienced it due to their riding styles, others adjusted their riding styles to avoid the range where surging appeared, and others delved into rather extensive adjustment or even modification of the fueling system, sometimes irreversibly.

Best,
DeVern

 

[ksdcr]

I have a well used R1100 RS, and over the years, used both the Iridium, and the Autolite 3923. I did not experience any real world benefit from the iridium’s. Went back to the 3923 Aultolites, and I find that they do improve the minimal surge that my bkie had. The one caveat with the 3923, is that they need to be change around 5-7 thousand miles, but are very inexpensive.

 

[pauls1150]

Iridium plugs will last longer but are indeed more expensive; they're also more likely to crack at the insulator tip if/when you need to adjust the gap.
I used the 3923s in my 1100 and liked 'em.

 

[robsryder]

Here are the bosch plugs as shown on the Max BMW parts fiche for the R1100RS. Next are the new bosch and autolite plugs for the R1100RS from BeemerBoneYard. I did not see Iridium plugs on BBY for the R1100RS.

 

[ksdcr]

Here are the bosch plugs as shown on the Max BMW parts fiche for the R1100RS. Next are the new bosch and autolite plugs for the R1100RS from BeemerBoneYard. I did not see Iridium plugs on BBY for the R1100RS.

View attachment 99996
View attachment 99997View attachment 99998

I usually find the autolite 3923 at my local auto parts place for about 4 bucks.

 

[GTRider]

I usually find the autolite 3923 at my local auto parts place for about 4 bucks.

Prezackly!

https://www.oreillyauto.com/detail/c/copper-core/autolite-copper-core-spark-plug/ato1/3923?q=Autolite+3923&pos=0

Some also like to mark the plugs and index them so the open gap faces the centerline of the cylinder bore.

Best,
DeVern

 

[ksdcr]

Prezackly!

https://www.oreillyauto.com/detail/c/copper-core/autolite-copper-core-spark-plug/ato1/3923?q=Autolite+3923&pos=0

Some also like to mark the plugs and index them so the open gap faces the centerline of the cylinder bore.

Best,
DeVern

I have heard of “indexing”, but never tried it. What is the process?

 

[GTRider]

I have heard of “indexing”, but never tried it. What is the process?

Rereading this, I’m smacking my forehead and remembering that the 1100 plugs are centered in the head so it’s a moot point. Sorry for the confusion!

On bikes with offset plug holes, like the airheads or a lot of older car engines, one could use a sharpie to make a mark on the plug’s porcelain in line with the open side of the plug gap, opposite the ground electrode. When the plug is installed that mark should ideally point toward the centerline of the cylinder bore, not away from the centerline. Not a big deal with today’s fat spark ignitions, but was often done back in the days especially on competition rigs. “Any small edge” kind of thing…

Best,
DeVern

 

[PGlaves]

Rereading this, I’m smacking my forehead and remembering that the 1100 plugs are centered in the head so it’s a moot point. Sorry for the confusion!

On bikes with offset plug holes, like the airheads or a lot of older car engines, one could use a sharpie to make a mark on the plug’s porcelain in line with the open side of the plug gap, opposite the ground electrode. When the plug is installed that mark should ideally point toward the centerline of the cylinder bore, not away from the centerline. Not a big deal with today’s fat spark ignitions, but was often done back in the days especially on competition rigs. “Any small edge” kind of thing…

Best,
DeVern

Yes, but! Indexing wants to ensure that the ground electrode does not shield the spark from the incoming fuel charge so the open gap ought to be oriented toward the intake valve. The issue with the triple ground and double ground plugs was/is that shielding from the incoming fuel charge was more likely to happen. One of the reasons that some 1100s surged badly and others not so much was the randomness of plug orientation. Even minor variations in torque can vary the orientation of the ground electrodes. Stock car racers would vary the thickness of the plug washers (shims) to vary the orientation of the electrodes.

Ah the stuff I learned reading Smokey Yunick in Popular Mechanics (or Popular Science) in the 1950s.

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