Autolite 3923 spark plug

I've read on the Internet BWM Rider's webite about the aftermarket Autolite spark plug (as published by Rob Lentini). My buddy just changed his GS over to Autolites and is happy with the result. So, I took and plunge and bought a set Sunday and installed them. However, the plug is MUCH longer than the twin electrode Bosch plug (I believe it's the F6DDC) that I took out of my bike.

Also, the plugs as purchased are NOT gapped at 0.8 mm as implied by the IBMWR article, but at about 1.09 mm (as indicated by my feeler gauge).

Has anyone had issues using these plugs? I've only ridden a few miles since changing the plugs, but I'm wondering if I should change. The bike seemed smooth, but new plugs should help some.

BTW, my 95RS has very little if any surging. The Bosch plugs were a little darker than I expected, though.

Thanks,
Jim

hi jim,
don't want to get into the one brand better than the other controversy, someone else can do that, but i would never put in a plug that wasn't the same size.
jerry

My 2003 R1150R has only 2200 miles on the odometer. I noticed a very slight hesitation at 3600-3800 rpm in 2nd and 3rd gears, nothing I couldn't live with but something I wanted to improve.

I installed Autolite 3923s set to .034" (within bmw spec) about 350 miles ago. I immediately noticed quicker response at the low rpms, especially at low speeds in 1st and 2nd gears. The new plugs also seemed to make a difference in the hesitation described above, eliminating all but the most imagined "surging." Of course, some of the improvement could be attributed to breaking in. Whatever the cause, the bike is running well.

Regarding the length, the 3923s appeared to be about 1mm longer than the stock NGK plug. Not enough to make a difference, IMO, especially since many have used them successfully.

The 3923's will work fine in the R1100. Yes, they are longer than the 2 prong plugs, but if you go back to ancient history the oilhead came with a 3 prong plug which is the same length as the 3923 and equivalent plugs. Long story short, there are dozens of oilheads running with the 3923, none of them have ever had a clearance issue.

just to be clear; i have also used 3923's
in my 1150. first time laid 'em next to oem champion plug and didn't see any difference in size.

jim had stated they were a "lot" longer than the bosch that came in his bike.

if i found that to be the case, i'd rather error on the side of caution, and do some checking first.

have nothing against the autolite plug. in my case didn't see any improvement in performance.
can't beat the price though.

The 1100 and 1150 do not take the same plug - same size but different heat range. The 3923 is not the correct heat range for the 1150. The correct for the 1150 is the Autolite 3922.

I should clarify what I mean when I say that the Autolite plug is longer. The distance from the base of the threads (the shoulder of the plug that is torqued against the cylinder head) to the end of the threads is exactly the same between the two plugs. The difference is that the single side electrode on the Autolite plug goes over the top of the center electrode, whereas on the Bosch dual side electrode plug, the two side electrodes come to the side of the center electrode. This makes the plug longer by about 3-4 mm.

My dad is an auto mechanics instructor and has 40 years of drag racing experience. When I spoke to him about the difference between the two plugs, he said something that made a lot of sense. Since electricity always follows the path of least resistance, the spark will NOT split simultaneously between the two electrodes on dual (or triple or quad) side electrode plugs. The spark will always jump to the side that is closest to the center electrode until there is carbon buildup on that electrode, then it will jump to the other electrode. So there is probably no performance benefit to a multiple side electrode plug, but it may last longer because the side electodes only see some fraction of the total spark events during the life of the plug.

Thanks for the feedback.

lazygoodan said:

I should clarify what I mean when I say that the Autolite plug is longer. The distance from the base of the threads (the shoulder of the plug that is torqued against the cylinder head) to the end of the threads is exactly the same between the two plugs. The difference is that the single side electrode on the Autolite plug goes over the top of the center electrode, whereas on the Bosch dual side electrode plug, the two side electrodes come to the side of the center electrode. This makes the plug longer by about 3-4 mm.

Click to expand...

More than likely the plug is a different heat range, it may also be because of the different manufacture, stick with the correct heat range plug, you can cross reference your original plug number to whatever other brand plug you may choose to try.

My dad is an auto mechanics instructor and has 40 years of drag racing experience. When I spoke to him about the difference between the two plugs, he said something that made a lot of sense. Since electricity always follows the path of least resistance, the spark will NOT split simultaneously between the two electrodes on dual (or triple or quad) side electrode plugs. The spark will always jump to the side that is closest to the center electrode until there is carbon buildup on that electrode, then it will jump to the other electrode. So there is probably no performance benefit to a multiple side electrode plug, but it may last longer because the side electodes only see some fraction of the total spark events during the life of the plug.

Thanks for the feedback.

Click to expand...

Your Dad is correct, the dual prong plugs are over rated, you can see this when you put a car/bike whatever on a scope and Dyno, I never saw any increase in performance with split fire no matter what brand plugs (I used to be blessed work in a shop that had a Dyno, Scope and 4 gas analyzer)
We saw better results with dual pluggin the heads, then you need to change your timming.

The part of them lasting longer is still debateable but not unproovable

Tom

I've looked at spark plug cross reference lists and NGK code keys at various websites, but I can't find an exact cross reference for the stock BKR7EKC for the R1150R, probably because it's a dual ground plug.

In NGK code, the numeral after the initial letters denotes the heat range, from 2=hot to 11=cold. The NGK BKR7EVX-11 and BKR7E-11 both cross reference to the Autolite 3922, which seems to indicate that the 3922 is the correct heat range for the "7" series NGK plugs in the R1150. However, the hotter "6" series NGK plugs cross reference to the Autolite 3923, suggesting that the 3923 is hotter than the stock BKR7EKC and probably not the plug to use in the R1150R.

So then, what gap to set the Autolite 3922s for an R1150R? According to the NGK code charts, the "11" suffix after the dash indicates that both the BKR7EVX-11 and BKR7E-11 are "wide gap" plugs (1.1 mm / .044"). Do you suppose the Autolite 3922s should also be set to that wide gap? Or should they be set to the 0.8 - 1.0 mm gap specified for the stock plug?

Follow-up:

I tried the Autolite 3922s gapped to .032" (BMW spec .8mm+) in my R1150R with even better results than the 3923s. I guess it pays to use a plug with the correct heat rating! Thanks to saab93driver for the tip.

Joe D

I have used the autolite 3923s for 30000 miles with no problems. they MUST be gapped to .032/.031 They are way out with their factory spec. you will notice the difference.
I have Dyno'd my GS with both plugs with no change.
A plug is not going to void a warranty unless it falls apart into the cylinder and is not OEM.
AS to the surging ...its not a plug problem...it is an FI. prob. the new dual plug is an attempt to fix it but Fuel mapping is the key.
20.00 canadian is a bit much for a plug.
Thats my 2 cents.