Correct spark plug for 1924 Model D Elto Ruddertwin

[Monte NZ]

Could someone please let me know the correct spark plug for my above motor.
The motor came with Champion D-16 plugs, but I’m not sure if these are correct, as they are very sooty after a run.

Thanks in advance.
MonteNZ

[RICHARD A. WHITE]

Try Champion R11’s if you can get them, they run well in my 1925 model C

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[Monte NZ]

Thanks very much Richard for your prompt reply.
I will try and get a couple.
By the way, my motors serial no. is D27342.

Thanks once again.
MonteNZ

[RICHARD A. WHITE]

C23336 is mine

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[garry-in-michigan]

Peter Hunn’s "The Old Outboard Book" lists a page from Champion from 1954 (Page 298 in the third addition) that shows the D model Elto Light Twin (AKA Rudder Twin) using a 7 Champion spark plug. Then on page 300 it gives an update on Champion spark plug numbers. There it wrongly equates the 7 and C7 to a D16. The Champion C7 is a hotter plug than the 7. The latest number for the 7 is Champion 516. The latest number for the C7 is Champion 526. These given numbers are educated guesses by the factory and actual plugs used will depend on load, temperature, humidity. and alditude. At one time the quality of Champion spark plugs made them the standard of the industry. Outsourcing to reduce cost has made this no longer true. Good luck on finding the proper spark plug . . . 😎

[The Boat House]

I’ve never had good luck with Champion’s
including the D-16. I use the AC C-87 in
my Super Eltos if you would like to have
another option.

[garry-in-michigan]

The AC C-87 aligns perfectly with the Champion C-7, which I believe was the original spark plug used. . . 😀

[Monte NZ]

Thanks Garry for the charts and comments and you too Tubs for your information……..much appreciated.

I am down country at present and had hoped to give the motor it’s first lake run since I bought it in 1974! Unfortunately the weather isn’t being being cooperative, with a lot of wind!
I have had it on loan to a museum for the last 25 years and feel that it is long overdue for a good run!

At Richard’s suggestion I tried yesterday to buy two Champion R11 plugs locally, but no luck, so
I will wait until I am back in Auckland and see how I get on there and with the other plug suggestions.

Interesting to note that NGK seems to be the most common plug brand here in NZ. However, I don’t know if there is an equivalent in in their range.

Thanks very much once again. It will be interesting to see how I get on.
MonteNZ

[roalco]

NGK does makes equivalent sized plugs, their A-6, A-7 and A-8 (or AB-6, AB-7, AB-8, if you want a conventional 13/16" hex, rather than 1") are 18mm, 1/2" reach, with 6 the hottest and 8 the coolest in their heat range.

[RICHARD A. WHITE]

I honestly had no idea what my R11’s were for, I just had a pair that fit the motor and ran with them…..LOL
Probably not the best plug for the motor but they look period correct and they work so I will run them.

http://www.richardsoutboardtools.com
classicomctools@gmail.com

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