NGK Surface Discharge Spark Plugs

[ozracer]

Does anyone know what the part number is for NGK surface discharge spark plugs for an NC30 in a 10 heat range? Tried searching but couldn't find anything.

[Cammo]

R847-10.

I got mine NOS from Japan, I don't think NGK make them anymore.

[ozracer]

Thanks Stickshift. I just did a search on google and found a few places in the US that stock them for around US$20 each.

[Cammo]

That's a good price mate.

I need to get a spare set, might check them out.

[CMSMJ1]

Can you tell me the whys and wherefores of these?

is it to allow more combustion chamber and tighter piston to head clearances?

come on...my race bike asked me and I want to know the deal..

[Cammo]

Mark, I think they are less prone to fouling. There may be other advantages but this is the word. Maybe Mr France or other can add comment, as many new 600's also recommend an NGK SD plug for the track.

I'm sure there's more tech to it than that.... it might just be that there's nothing adjustable about them (more consistent): they're made for a certain bike model/purpose.

I've never had any issues with the standard plugs, but when you use the hrc carb setup it's pumping a fair bit of of fuel in the engine at all revs/loads, and the last thing you need are dead plugs at the track!

At the price above they're cheaper than std plugs for me! These are the plugs that are recommended in the 30/35 hrc manuals.

[Neosophist]

I think thats the main benefit.

NGK say on their website.

"Surface Discharge™

Surface discharge spark plugs are used in many fishing boat applications, where alternate high-speed running and very low-speed trolling can cause fouling. The surface discharge plug helps keep the firing end clean under these extreme conditions for continued operation."

Surface and semi-surface discharge firing tips are less sensitive to voltage requirement increases due to gap growth(wear). Note the concave cut on the ground electrodes for even Gap growth (wear). In addition, this type of construction aids in burning away the carbon which can act as a bridge between the center electrode and plug shell. This bridging can cause plug misfire.