Spark Plugs

While I realize the job that a spark has to do is sorta simple, there must be a lot of complexity associated with them since there are dozens of types of plugs..., or are there (?). My Dad, the real mechanic in the family, was determined to use the one shown in the Owner's Manual. For the 8N that was Champion H-10. Now I cannot even find that plug at NAPA or the other auto box stores, though they all have interchange numbers and several "choices." Some they push as Champions have a symbol on them which is similar to the Champion logo, but it doesn't say Champion anywhere and I suspect they are cheap China copies. Even YT has two plugs for 8N's and other models, one of which seems to replace H-10, 12, 16, and 18; as well as many others. Many here recommend Autolite 437's, which I tried once but they seemed to get carbon chips and deaden a cylinder, but I recognize that could have been happenstance. I am interested in the truth (if there is "truth") about spark plugs, having researched the archives didn't help much. Has all this complexity been overthought and the only thing that is material is the thread size and length to get it in the right place? If heat ranges are important, how does one plug replace dozens of others with multiple heat ranges?

I'm no spark plug scientist, but I found champion h-10 plugs at the local Tractor Supply co. I've read auto lite 437's are better, so that's just what I use. I've got a set of brand new H-10's sitting around somewhere.

Don't over-think this.

It's a low hp, low compression, low rpm 60+ year old flathead engine.

It's not a modern vehicle. The brand of plug you use isn't going to make any difference in performance, IMHO.

I use 437's & H12's in 4 8N's. Can't see any difference. My guess is any modern plug that fits the heat range will be fine.
75 Tips

As Bruce says,don't over think this! The single most important thing in most engines is the reach of the plug so it doesn't hit the piston,the heat range comes into play more in two strokes than it ever will in a flat head design.H-12's or 437's will work just fine,we're only talking about low 20's HP.

Ask the NAPA IDIOT to check stock for Stock #844 Champion, which is another name for a H10.

No matter how long the reach.....it will never contact the piston in an 8N. Perhaps a valve. :wink:

As bruce said. this issue is like horse shoes, hand grenades and thermonuclear weapons.

Close counts.

don't overthink this.

You're right, not overly complicated.
Reach is important though, even on a flathead N engine.
If it is too short and doesn't fill the threaded hole, the remaining
threads will foul with carbon and you may not be able to get the
correct plug in without chasing the threads. What you chase
out may get stuck in a valve. Probably temporarily.

If it is too long and the ends of the threads stick below the head,
they may carbon up and make it difficult to remove the plug
without damage to the threads in the head or leaving chunks
to get caught in valves, etc.

Yes, I'm well aware these could be considered extremes, but
they should be considered. Match the thread length, play with
the heat range as desired. Might help with an oil burner.

Brand? I'm not sure what you're buying from any brand nowadays.
But almost all of the manufacturers have a reference table on
there website for you to view. Assuming they are accurate.

Your window into the world a spark plug lives in.

https://www.ngksparkplugs.com/about-ngk/faqs/spark-plug-faqs/how-do-i-read-a-spark-plug

I will not use a Champion unless it was the desalinated OEM approved plug then I am quire about its origin. If I use them I source them from the OEM dealer not a parts house, it will be the same plug supplied from there OEM malefactor that's handed to there dealer mechanic . I don't use Autolites any more because low bidder got the contract, Autolite sold there sole

Autolites and those damm Bosch plugs are garbage these days.

NGK are Denso are a good there quality is second to none. Across the board NGK/denso a what I find to be the most used OEM spark plug.

Its a lot of work to research what is the original plug and worth the difference in price to get them. Because I work on all makes and don't like to chase a spark plug induced misfit/misfire/quality issue by no means will I suggest close counts. It don't work that way anymore are I may be the only one that inspects spark plugs
new out of the box. I have several sets of new Autolites on the shelf I will not use are sale they are defective new in the box never installed. They may be good enoufh for the bean counters but not good enoufh for the man that has to chase down the issues they cause.

(quoted from post at 07:51:00 06/30/16)
Your window into the world a spark plug lives in.

https://www.ngksparkplugs.com/about-ngk/faqs/spark-plug-faqs/how-do-i-read-a-spark-plug

I will not use a Champion unless it was the desalinated OEM approved plug then I am quire about its origin. If I use them I source them from the OEM dealer not a parts house, it will be the same plug supplied from there OEM malefactor that's handed to there dealer mechanic . I don't use Autolites any more because low bidder got the contract, Autolite sold there sole

Autolites and those damm Bosch plugs are garbage these days.

NGK are Denso are a good there quality is second to none. Across the board NGK/denso a what I find to be the most used OEM spark plug.

Its a lot of work to research what is the original plug and worth the difference in price to get them. Because I work on all makes and don't like to chase a spark plug induced misfit/misfire/quality issue by no means will I suggest close counts. It don't work that way anymore are I may be the only one that inspects spark plugs
new out of the box. I have several sets of new Autolites on the shelf I will not use are sale they are defective new in the box never installed. They may be good enoufh for the bean counters but not good enoufh for the man that has to chase down the issues they cause.

Click to expand...

How do you check the new spark plugs out of the box? Ohmmeter? Spark tester?

Short version , Buddy's truck ran bad after the tune up (autolites) replaced the new plugs with the old one and it ran great . Yep autolite sold there soul . Oreos are moving to Mexico for $4 a day labor but I bet they will sell for the same price .

I never had a problem with a Champion spark plug in any engine in which the engine owner's manual specified Champion spark plugs. I tend use whatever brand of spark plug the engine manual specifies. But then again, I am a firm believer in using OEM parts including filters and lubricants. Our local Case dealer sells Case branded engine oil and Hytran cheaper than our local coop sells allegedly comparable Countrymark product. Motorcraft oil and filters are used in the Ford Vehicles and AC filters and Mr Goodwrench oil goes in the GM vehicles. And I am not going to drive 100 miles to save $5.00 on a 5 gallon bucket of oil nor anything else for that matter.

You could ohm them for what that would be worth most of the time you can see the defect....