Spark plugs.

[raindodger]

Hello.
         About a week ago, I tried an experiment.  I had long thought that the basic design of plugs had a flaw.  Let me explain, with a standard plug, the earth electrode is bent over the top of the centre electrode.  This has the effect of shrouding the spark from the charge in the cylinder, also there would be a strong quenching effect on flame propagation.  So, I found 2 plugs in my junk box, same make same heat value and modded them as follows.  With pliers, I twisted the earth electrode sideways and downwards.  In this position, the spark will jump from the side of the centre electrode, to the side of the earth electrode, and be in full 'view' of the charge.  Rather like the old triple electrode Lodge plugs of yore.  I installed the plugs and went for a 10 mile ride.  The bike started easily, but it always does, and ran normally with no noticeable difference in performance.  But, when I returned to base, I noticed that the idling speed was higher and had to adjust the throttle stop  to bring it down.  So, why, was it the mod, or something else?  I changed nothing but the plugs.  The bike continues to run well, so I'll try the mod on the B31 next.
I wait in trepidation to be shot down in flames.
Regards.
Tim.

[bsa-bill]

Hi Raindodger
such plugs can be found on the market already with several side facing contacts, never found them any better than ordinary plugs really.
I understand your theory but I wonder if it matters much to normal riding - perhaps racers will comment, I do recall racers "indexing"? plugs, I think this was to get the spark facing the incoming charge but I could be totally wrong

[morris]

Hi Tim, wont' shoot you down, after all it's your bike and your money at stake...
Just a thought, but so many things have been tried regarding spark plugs It would probably take up all free space on the server to give just an overview...
If it really made a difference, spark plug manufacturers would have been making them that way for a long time now.
I think it's more important to have a strong spark. I noticed on the SA since I converted to electronic ignition it became much more reliable, runs better and is now a first kick starter whether hot or cold.
Which it would probably also have been with a magneto in good order come to think of it. That's why I have sent the old magneto off to be overhauled to do service on the plunger.

[BSA_54A10]

You are not the first one to ponder on this point.
The usual "fix" was to put additional washers under the plug so that the earth strap pointed towards the inlet valve or cylinder wall depending which theory you subscrided to.
This is commonly referred to as "indexing the plugs".
I have always liked the idea of having the earth strap facing the inlet port for cooling reasons.

[Triton Thrasher]

I hope one of your bent electrodes does not fall off.

Here's something else that people do.

[raindodger]

Thanks for the replies, Gents, and for the lack of bullets!  I have been hunting for multi electrode plugs, but cannot find them with 1/2" reach.  I did a club run of 150 odd miles at the weekend and the bike ran really well, no trouble at all, but I'll try TT's mod with a file to see if that makes any difference.  I've got many old plugs in the shed.
Thanks again.
Tim.