BSA M21 Sparkplug

[watts]

Hello

What is the correct one, my book says Champion N8.

The previous owner gave me a NGK B6ES is this right?

Any recommendations?

Thank you

Matthew

[Ian C]

From the plugs mentioned, you have an Alloy Head on yours? AFAIK, the Champion N8 was phased out and was replaced by the N5C which has an NGK equivalent of B6ES, so the NGK you have 'should' be ok. Be aware though, that on some plugs the electrode is very near the inlet valve which may hit it and close the gap! Don't ask how I know, but I just fitted an extra copper washer under the other spark plug washer to space it up a bit.

[watts]

Hello Ian

Thanks sounds like a good idea it did cross my mind as I seemed to wind the plug in for ever!

Cheers

Matthew

[maddogmargetts@yahoo.co.u]

Is ES not a long reach? For a cast iron head this is not correct and will bash against the piston. As Ian C suggests you can use an extra spacer. I did  on a previous spark plug and it worked fine.