spark plug gap

[finsally]

Hi.according to the service and technical booklet,the correct spark plug gap should be 0.8mm (0.03 in) also the Haynes Manual states this.

It seems to me to be a very small gap,the manual can't be wrong!!...why has the gap got to be so small....does everybody adhere to the manual.

Cheers Bob

[boxermania]

You are in the right ball park....anything from 0.030" to 0.032" will work well

[finsally]

Thanks for your reply,I may be wrong but does it not say (0.03) in the manual
Cheers Bob

[boxermania]

Thanks for your reply,I may be wrong but does it not say (0.03) in the manual

0.03 in inches is the same as 0.030"

[Xdot]

I'm using original plugs with the twin electrode. The gap isn't between two flat surfaces as with a traditional sparkplug but is between the outer curve of the inner electrode and the semi-circular shape on the outer electrode. I had trouble both setting and measuring that curved gap with my feeler gauge. I still don't know if it is 'right' but since my bike fires right up each time I suppose it's close enough.

[boxermania]

Xdot, if your bike is the two plug model consider using the Autolite 3923 variants, less expensive and great service.

[Xdot]

Xdot, if your bike is the two plug model consider using the Autolite 3923 variants, less expensive and great service.

2002, Uni-spark engine.

[boxermania]

Xdot

I'm sorry, I didn't myself clear in the earlier post, I meant the two spark plug model rather than the 4 plug model

[Airman]

Xdot, if your bike is the two plug model consider using the Autolite 3923 variants, less expensive and great service.

2002, Uni-spark engine.

I think any auto supply could sell you a sparkplug adjusting tool with the wire type gages that would work well on the NGK BKR7EKC-N .....I guess they're dual ground plugs. I just installed a pair of these and they work well on my `03. You and I are fortunate in some ways not to have the dual plug setup. We never have to worry about the condensers going bad at least.

As for boxermania's recommendation of the Autolite 3923s: I had a pair of them in the bike for at least 30k before one of them developed a stumble at idle. Both were gray and fairly clean when removed last week. I was thinking when I changed them that in spite of the fact that the plug wires looked ok, I know those things break down with time and perhaps I should replace them as well.

[macx]

After reading this thread, I was doing some research on spark plugs, sort of following up on information I had found some time ago incl. stuff like spark jumping more easily from a sharp point or edge than from a blunt or rounded edge, etc.

Now I found additional information saying that if a spark can jump more easily between the center and grounded electrodes that it will do so earlier in the "rise" of spark energy building up and therefore result in a smaller spark kernel.

Also that in a plug with more than 1 grounded electrode the spark will jump following the easiest path so will only jump to one irregardless of the number of grounded electrodes.

http://sparkplugs.com/
http://www.se-r.net/engine/specialty_spark_plugs.html

The information included claims that the specialty sparkplugs (platinum, irridium, etc) primarily have advantages such as lasting longer, helping a weak ignition system because of the lower spark energy required to jump the gap, etc. The last article written by a PH.D cites tests done by Jacobs showing that regular plugs actually made a tad more power on the dyno on an engine with a good system.

Last but not least I found a post in "another BMW forum" (result of a Search) saying that Autolite 3923's were actually the proper heat range for BMW 1100 oilheads while 3922's were the proper heat range for 1150's.

So, having waded thru all that information, I think I'll try the 3922's next time around. Just have about 1500 on a new set of oem type plugs, too expensive to throw away while they're still working OK.

[Ol' Jeffers]

I'm a ol' boy and when I was building British bikes back in the '60s all plug gaps were set
at around 25thou (0.025in) and all points including magnetos at 12 to 15 thou. right across
the board! How times have changed!

[Xdot]

LOL. I used to carry some 400 grit sand paper to clean my points in a 66 Mustang that I drove forever. At one point I carried enough tools to change a valve on the highway. Funny what graduating from college and getting a good job will do for you! Would it be possible to carry enough tools in my saddlebags to swap out a tranny input shaft on the road side?