Triumphrat

dogtired · 12-20-2009, 07:20 AM

Just went and pulled the plugs out of my '71 Bonnie.

Running a tad rich...

All the books tell me to use a Champion N3 (or equivalent), it has a Boyer, but it is an analogue Boyer, so the N3 should be OK? I ended up with a NGK B8ES which is the correct cross match to a N3.

Pulled the old plugs out and they were NGK BP5ES which cross reference to a Champion N12YC.

The old plugs have possibly an extra half a mm of thread measured by placing the threads against each other in a top to toe position. And as in the pic the old plugs electrode and hookie thing is much more "proud" out of the end of the plug than the N3 Equivalents.

Anyone come up with a possible reason for the P.O. using the different plugs, would there possibly be a mythical performance reason?

I also "gapped" the old plugs with my feeler guages, and they were set at around 30 thou, as opposed to the recommended 25 thou in the manual. The new NGK's are also "factory set" at roughly the same 30 thou gap. I have never had a misfire problem with the old plugs at 30 thou, should I just screw the new plugs in at the same factory setting they came out of the box in, 30 thou?

I am bit worried the above question might have a piece of string answer, or be like an oil thread, (shudder) and have no black and white answer.

Anyone game to answer?

Notes: -
Cross reference page is here I recommend that page for a bookmark. Just use the search function in your browser to find your plug.

Caulky · 12-20-2009, 08:19 AM

Use the correct plugs with the right gap.
The gap (.025"?) ensures your timing is right (if its set correct) AND the duration of the spark for combustion.

JTT · 12-20-2009, 08:24 AM

I'm not sure the "correct" plug (although I believe it is the N3 or B8es), but can tell you that the BP5ES is a considerably hotter plug. Hot enough that I would have concern running it particularly if you ever run the bike hard. NGK numbers work the reverse of Champion ones...NGK- lower number = hotter, Champion - lower number = colder.

The "P" in the BP5ES stands for "projected" meaning it protrudes deeper into the combustion chamber. This allow the spark kernel to be deeper into the gas flow...if you have the clearance...if not the piston hits the head (not a problem for these Brit bikes).

OzBloke · 12-20-2009, 08:28 AM

IMHO, bang em in at 30 thou, and give them a go for 100KM or so. If they play up and miss, regap to 25 thou. If they still play up, go to Champion N3C's. I've had a few probs with NGK's, and stick to Champions now.

I take it your not running suppressor leads or plug caps? If you are, I'd recommend you gap to 25 thou first up.