Champion plug numbers

[SwedScott]

Hi

When rummaging trough my stock of new old spark plugs I found some Champion plugs marked 16 and some marked 17. Please note that this is old plugs with no prefix. The Champion numbers has changed several times so it’s not easy to keep up. Is any of those suitable for a 1928 TT rep? To my best believe Champion 17 is in the same range as Lodge H1 (and NGK A6) and Champion 16 is like Lodge H3 (and NGK A7), am I right? Old conversion tables isn’t too reliable, so any “hands on” information would be appreciated.

Best regards

Leif

[PaulR]

The Champion plug D16 is still available and equates to NGK A6
Other similar plugs are Lodge CV., KLG M50 in the 18mm sizes
Information is available from our friends at the Green Spark Co
who are on the net and are very helpful… Regards

[BRIAN MARSHALL]

The ‘recreated’ KLG M50 is interesting to Scott owners as it is a longer reach than all the others. KLG were taken over by Smiths Industries in 1927, and Kenelm Lee Guinness committed suicide in 1937. Vintage Bugatti owners were desperate for long reach 18mm plugs, and so Tim Green was able to purchase the KLG tooling from the remains of Smiths Industries, and have a batch of the M50 plugs made. If fitting them to a Scott that has done any mileage on the shorter reach plugs it will be necessary to run an 18mm tap down the plug hole in the cylinder head to clear carbon deposits from the previously unused threads. Apart from the spark being less shrouded, the new plugs will give a slight increase in compression too !
Brian

[SwedScott]

Thanks for the advice!

Just to make sure: is the old Champion 16 the same as the more recent D-16? Champion have had so many changes in their numbers so you get easily confused!
Furthermore I noticed one strange thing. The ferrules that holds the spark plugs seems, on my engine, to be counterbored. Under the 1/2″ thread reach the hole is bigger! So fitting a longer reach plug is no good, after some use you probably not get it out due to carbon buildup!

Best regards

Leif

[Barrie]

The ideal fit is the body of the plug should be flush with the combustion chamber ,
not only will this ensure the threads stay clean, but also the plug gets to and maintains it’s correct temperature.

[SwedScott]

Hi Barrie

Do you think that there will be no carbon buildup in the little space between the plug thread and the hole? The thread in the ferrule is only 1/2″ long, and the rest is just a plain hole until it reaches the combustion chamber. Is it that way it was always made? I have not had a close look at it before, I imagined that there should be a long thread in the ferrule (under the soot). But I had a close look today and it’s like described above.

Best regards
Leif

[Barrie]

I do not run a non detachable head, but a know a man who does and I will be seeing him and others in the week ,I’ll see if I can get an answer.

[Author]

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