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Correct Spark Plug Size

Sat Dec 20, 2003 8:01 pm

Can anyone tell me what is the correct size plug to use in the Cub? I had a Champion D16 in one Cub, Champion's site calls for an RD18Y or D18Y. I had an AutoLite 386 in another Cub and AutoLite's site calls for a 3116. The Cub specs call for a .023 gap, but both AutoLite and Champion state a .025 gap for the Cub. :x

Sat Dec 20, 2003 8:50 pm

Most people use Champion "D-21" for all around normal usage.

Sat Dec 20, 2003 11:32 pm

I've heard some people say the current Champions aren't any good, but I've been using Champion D-21 plugs for 15 years on a work cub.

Sun Dec 21, 2003 1:02 am

I don't use them on cars but they very good in my Cub

Sun Dec 21, 2003 4:36 am

I have had Champion D-16 and D-21's in Ellie-Mae. She is now sporting NGK 2245 A-6's and runs better than ever.

Sun Dec 21, 2003 2:39 pm

Anybody besides me using A-C Delco C-86's? That's all I can ever remember having.

Mon Dec 22, 2003 12:44 pm

I have run D15Y champion for 13 years now and never had a problem.

Rudi - are you sure that's not a racing plug - I had a 900 Turbo 'SPG' SAAB that used the same NGK plug.

Mon Dec 22, 2003 2:56 pm

Hey Guys:

Don't forget, the heat range of the plug is more important than the brand. All the plug has to do is light the mixture. If a plug lights the fire, then that's all that is needed.

Remember, a hot plug is recommended when the engine is used very little, for a short time or may be pumping a little oil. A cooler plug is recommended for a clean burning engine that works hard for extended time periods. Sometimes you just have to experiment with different ranges to see what works best for you.

And if I don't get another chance, Merry Christmas and Happy Holidays to each of you.

Mon Dec 22, 2003 4:02 pm

Yo's Dad wrote:Hey Guys:

Don't forget, the heat range of the plug is more important than the brand. All the plug has to do is light the mixture. If a plug lights the fire, then that's all that is needed.


Sonny,

You learned good. I'm proud of you. :lol:

If I remember right, I compared the plug to the fuse on a firecracker. Once it fires reliably, it makes absolutely no difference in the Bang what the fuse is made of. :idea: As far as plugs are concerned it is the heat range, not the make that determines whether it remains in condition to fire reliably.

Mon Dec 22, 2003 6:52 pm

George:

Thanks for the quick lesson, I appreciate it and may have learned something, ifn I can keep it in me head :roll: .

Sooo, a Champion D-16 is a colder plug than the D-21 or the NGK 2245 A-6?

If this is the case, then as Ellie-Mae only gets to frolic after a snowfall, she should be running hot plugs in the winter. As she runs a lot in the summer, then I should change to say the D-16's which were working real well this summer.

Am I getting it :?: :idea: :?:

Mon Dec 22, 2003 7:39 pm

Rudi wrote:George:

Thanks for the quick lesson, I appreciate it and may have learned something, ifn I can keep it in me head :roll: .

Sooo, a Champion D-16 is a colder plug than the D-21 or the NGK 2245 A-6?

If this is the case, then as Ellie-Mae only gets to frolic after a snowfall, she should be running hot plugs in the winter. As she runs a lot in the summer, then I should change to say the D-16's which were working real well this summer.

Am I getting it :?: :idea: :?:


Rudi,

Pretty close. As I understand it, the only reasons not to use the hottest plug possible is at higher temperatures their life is shorter and they can possibly cause pre-ignition. Therefore, I think it best to change to a colder plug only if they burn up prematurely or if there is a spark knock. For most of us the D-21 (or equivalent) will work best all the time, summer or winter.

The D-16 (colder) is a good plug but is more likely to foul than the D-21 (hotter) if the engine is less than perfect. The heat range refers to the relative operating temperature of the plug... not the intensity of the spark. The hotter plugs have the ability to burn off more deposits/oil/carbon... thus remaining cleaner.

Mon Dec 22, 2003 7:41 pm

This is where the old fashion plug testing machine that Nick mention on an earlier post, I've seen brand new plugs start to fail after a 110LBS. Strange but true. :roll:

Mon Dec 22, 2003 9:28 pm

George:

Thanks much. I think I will try the D-21's and see what happens. That is exactly what happened to the D-16's - burned up, toast, crispy critters with no get up and go - it all got up and went.

BTW, that is another tidbit of info to put into Tips and Techniques!

Mon Dec 22, 2003 10:25 pm

Well, after many posts on this thread, I am learning allot here! Since there are some many different brand plugs out there, all with various characteristics, I decided to try a few to see if I can "feel" differt results within my 3 Cubs. I have AutoLite 386 on one, Champion D16 in another, and now I just got a set of AutoLite 3116 (recommended at the AutoLite site for the Cub). Comparing the AutoLite 386 to the 3116, the 3116's firing tip protrudes a bit longer. I would guess that this would better center the spark in the combustion chamber. I'll pull my D16's out and compare them as well and maybe get a set og D21's as well. If the tip protrudes the same, then I would say the difference is only that one is hotter than the other. Just another facsinating aspect to learn with this old iron .... which still applies to newer engines of today! Thanks to all for the posts, thoughts, and advice.

Mon Dec 22, 2003 11:03 pm

I think you will find the D-16s do not have a projected tip. The Champion designation for a projected tip is a Y suffix, as in D-16Y.

Now, going back to the original question, which was probably not the intended question, the correct SIZE plugs are 18mm.
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