Autolite spark plug gap

[Dingo55]

Hoping someone can tell me the gap setting for these plugs in a 1999 r1100rt

cheers

Mark

[Jim Moore]

I've always used 0.030".

[Dingo55]

ok Jim 

Thanks

[dirtrider]

3 hours ago, Dingo55 said:

Hoping someone can tell me the gap setting for these plugs in a 1999 r1100rt

cheers

Mark

Morning Mark

 

Can we assume you are talking about the Autolite 3923 spark plug? If something else let us know. 

 

The 1999 1100 spark plug gap specification is .8mm  (.0315")  with a wear limit of 1mm (.039"). The wider the gap within that range the bigger spark you can get but that means that you reach the electrode wear limit faster (at less miles traveled).

 

So the gap can depend somewhat on WHY you are installing those  Autolite plugs. 

 

If you are just after installing a cheap spark plug & getting the longest life from them then use .031" (Jim's .030" will work just fine).

 

If you are trying to get slightly less light throttle surging, or get  a slightly better idle then set them wider (in the .035" range) but this will then require earlier replacement or at least earlier plug gap checking or re-gapping.  If the electrode gap gets much over .040" then you start risking plug wire leakage (arc-through) or possible coil damage.  

 

Another thing to keep in mind is that your BMW 1100 boxer uses a lost spark ignition system, that basically means that one side spark plug sparks center electrode positive & the other side spark plug sparks center electrode negative. It also means that both spark plugs spark at every piston up (like a 2 stroke engine) so your spark plugs basically see twice as many sparks per mile as a conventional 4 stroke ignition system.   

 

 

 

 

[BABABeemer]

I just purchased a four pack of Autolite 3923s on eBay and all four were “preset” to .040! Be sure to check new ones!

[Dingo55]

Morning DR

Only saw your reply just now

Thanks for that

Just gearing up for a 20K kilometer service

Saw Autolite plugs in the local store

Remembered that people on the forum were using them so got the number went back and there they were 3923's on the shelf

After picking myself up off the floor ( you can't buy anything for this bike locally except maybe oil and globes) I grabbed a couple at $5 each 

Bosch fr6ddc cost $20 each

So I figured 4 for the price of one what have I got to loose especially given that many seem to be using or have  used them

Is there any reason not to be using them?

Were you alluding to something in your last paragraph?

Don't know if I have experienced the surging that some speak of

Anything that might be construed as surging seems to disappear after a full service ie new plugs/valve adjustment/throttle syn

 

On the subject of throttle body sync has anybody ever thought if it would be possible to make access available to the adjustment area ie nut and knurled adjuster so that 

adjustment could be carried out more regularly without having to remove the tupperware?

I guess it would be around about the knee guard area

Thanks again

Cheers

Mark    

    

[dirtrider]

Morning Mark 

 

Were you alluding to something in your last paragraph?-- 

 

Just informing, BMW uses the more expensive  dual electrode spark plugs as OEM for a reason. With 2 electrodes, as one electrode wears the spark switches to the other (closer) electrode (usually tends to spark to the closest electrode so the spark keeps switching back & forth) this somewhat improves spark plug life.

 

With your new 3923 single electrode plugs just keep that in mind & don't go too long without checking the electrode gap. (they should still easily go the service recommended miles though).

 

If you remove the spark plugs for inspection it helps spark plug life to swap sides as that changes the sparking direction across the plug's electrode gap & even out the electrode wear. 

 

 

 

 

[Dingo55]

Hi DR

Thanks very much for that

So would you suggest a checking and swap left to right every 10.000 klms and then new ones at 20.000 klms?

Thanks again

Cheers

Mark

[dirtrider]

44 minutes ago, Dingo55 said:

Hi DR

Thanks very much for that

So would you suggest a checking and swap left to right every 10.000 klms and then new ones at 20.000 klms?

Thanks again

Cheers

Mark

Morning Mark

 

If you shop around on-line you can usually find those Autolite 3923 plugs for just over $3.00 each so personally I would just buy ahead then replace them anytime you have them removed after 6,000 miles of use. 

[Michaelr11]

11 hours ago, BABABeemer said:

I just purchased a four pack of Autolite 3923s on eBay and all four were “preset” to .040! Be sure to check new ones!

 

The 3923 plugs are always gapped too wide when you take them out of the box.  I adjust the gap to ,032 and mark the box so I know that they are ready to install.  They are so inexpensive, I just put in new ones at 10-12k miles.