# SO many sparkplug equivalents



## jimfarwell (Nov 25, 2014)

I wasn't sure where to put this question. It's not automotive, it has to do with small engines...but I suppose it does have automotive overtones, too, so....

Anyway, if any moderator can find a better place for this question, please feel free to move it.

My issue is this: I need to replace the spark plugs on all my small gas-engine equipment at our off-grid property. There are a lot of them -- 4 generators, 2 small mowers, 1 riding mower, 1 log-splitter, 1 band-saw-mill, 2 chainsaws, 1 rototiller, and a partridge in a pear tree. 

We shut the place down for five months every year, mid-Nov to Mid-Apr (...why is a long story, for some other time). All the equipment manuals say to change the spark plugs once a year, and a good time is whenever you are starting to use the equipment. I've ignored that advice with impunity -- I change them every 3 years, and have had no problems. I have a list of all the plugs recommended in the owner's manuals, and I take it to my local auto parts store. Every time, the counter man doesn't have the exact plug models in stock, so he gives me "equivalents". The equvalents have always worked. So, (you may ask) what's my problem? 

Well, just for squats and giggles, I looked up one of the OEM plugs. Just one. The manual for my Generac GP5500 says to get a Champion N9YC *or equivalent*. So I googled "equivalent for Champion N9YC spark plug". Up came a list of 7,286 spark plug model numbers from 314 makers. ...OK, I'm exaggerating...it was 74 models from 10 makers. But that's still a LOT of spark plug models. Shoot, 28 were from Bosch alone.

If you check the specs for a N9YC, it has a thread diameter of 14mm, a thread reach (whatever that is) of 19mm, flat seat type, hex size of 21mm, projected tip, and standard construction. Do they really make 74 different spark plug models, each and every one of which will satisfy all those specs?

And if they really do.....WHY DO THEY DO IT?

And is there any way of determining which of those 74 equivalents is the closest match to the elusive Champion 9NYC?

...Am I alone in the wilderness, the only one who gives a flying f...iduciary?


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## SeniorSitizen (Sep 10, 2012)

An important criteria of your list is thread reach if you want to avoid a knocking sound, possibly a hole in the piston and no spark after the first piston to top dead center or there abouts. I'm betting you get the drift.


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## ron45 (Feb 25, 2014)

I clean/gap the plug/s every year before use.

Going on my sixth year with the same plug for zero turn.

Got the same plugs in my 2008 Low Rider That I plan on replacing this season.


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## Porsche986S (Dec 10, 2017)

My 2 cents from years of DIY wrenching , the three most important areas of concern for a spark plug replacement are:

1.Have to be the correct diameter and thread pitch so they screw in .
2.Have to be the correct thread reach , this is to make sure there is no contact with piston.
3.Has to be the same or very near the correct heat range . Too cold of a plug it will foul easily . Too hot of a plug can cause detonation and piston damage . 

Having said all that with internet shopping at your finger tips with home delivery why not order online the exact plug that the manufacturers installed originally ? That way you are eliminating the " or equivalent " from the equation .


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## papereater (Sep 16, 2016)

I do common sense (which is not so common) plug inspection/cleaning too. They usually last for years. The once a year could be for high usage. The once a year change the plug whether it is bad or not is like the 3000 mile oil change mantra for cars.


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## ukrkoz (Dec 31, 2010)

Confused customer buys lots of wrong parts or parts that do not last and then keeps buying more.
hence the confusion.
As Russians say - you catch better fish in murky water.
Say, you have 10 plugs. Prep 10 plastic bags, take plg out, burn tips clean with propane torch, place in plastic bag and tape to the unit side or mark with Sharpie. 

Spray carb cleaner into plug hole before reinstall and hand crank it few times.
You leave them in, they only oxidize inside, in moist cold chamber. 

My Stihl runs for 6 or 7 years by now on the same plug....


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## lenaitch (Feb 10, 2014)

Why do they do it? Free market competition. There are lots of companies that make 'equivalent' gasoline and dish soap as well.
As mentioned, an equivalent plug needs to have the same characteristics (diameter, reach, heat range, etc.) to function properly and most small engines will run just fine on any of them. Experience may show that some engines run better on one brand than the other but often the use of engine will make that unnoticeable. Some higher performance engines might be sensitive to the internal resistance of the plug but I doubt that is an issue with house use engines.


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## jimfarwell (Nov 25, 2014)

Porsche986S said:


> My 2 cents from years of DIY wrenching , the three most important areas of concern for a spark plug replacement are:
> 
> 1.Have to be the correct diameter and thread pitch so they screw in .
> 2.Have to be the correct thread reach , this is to make sure there is no contact with piston.
> ...


Thanks. And thanks, too, to SeniorSitizen, who already clued me in on the thread reach. Your advice on heat range is welcome.

You're right, I can (and will) order the correct plugs for each engine. At least for those engines where I have manuals that tell me the preferred plug -- I have a couple of engines with no manual ANYwhere, that likely should be in an industrial museum. If I can't find the OEM's recommendation, I'll pull the plugs and buy the same again...or equivalents (lol). I know I can clean and gap the old ones, but after a while the gaskets get pretty flat and non-resilient -- I figure a new plug every three years is a cheap way to maybe help prolong the life-span of these faithful old friends.

But my original question was more about the abundance of identical (or nearly so) plugs, and why the plug-makers choose to make them. Just idle curiosity.


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## jimfarwell (Nov 25, 2014)

ukrkoz said:


> Confused customer buys lots of wrong parts or parts that do not last and then keeps buying more.
> hence the confusion.
> As Russians say - you catch better fish in murky water.
> Say, you have 10 plugs. Prep 10 plastic bags, take plg out, burn tips clean with propane torch, place in plastic bag and tape to the unit side or mark with Sharpie.
> ...


I was unclear. I DO end-of-season maintenance on all the engines. For each of them, I siphon out the gas tanks, run them until they quit, drain the oil, refill the oil, pull the spark plug and clean it with a wire brush (...though I've never burned them with a torch...might try that, if it helps), then gap it, use a syringe to squirt about 15 cc's of oil into the plug hole, and pull the starter to distribute the oil and lubricate the bore. Every third year, when replacing the plugs, I've also checked valve clearance -- after the first check, when I've frequently needed to adjust the gaps, I've seldom found any further adjustment necessary. But it's a habit now, and doesn't hurt to check. I use ONLY non-alcohol gas. My engines seem to appreciate the small amount of "quality time" I spend with them each autumn. I'm old and slow, I take my time, likely spend an average of an hour per engine. I keep the used oil, mix it with diesel, paint it on my posts before I bury them, extra protection against rot and bugs.

Before I bought our off-grid property, over the years I had several small engines die on me -- lawn mowers, gas weed-whackers, a chainsaw. I was careless about it, had enough cash to just go buy another when needed. But when I realized that I had a dozen pieces of gas powered equipment and a 120-mile round trip to the nearest quality repair shop, I figured I'd better start doing some preventive maintenance, so I started collecting all the info I'd need to get the right oils, plugs, filters, etc. When I first started doing it, ten years back, much of the equipment had come with the property when I bought it -- the engines were already old, and hadn't been much cared for. The first couple of years, it was a day-long chore that I disliked. Now, it's a routine, and sort of relaxing...gets me away from the wife and OTHER chores for a whole, blessed day. A couple of times I had a friend with me, and we'd talk and drink a couple of brews and enjoy each others' company. Good times.


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## ron45 (Feb 25, 2014)

If the spark plugs did good.

The name etc., is usually written on the plug.


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## jimfarwell (Nov 25, 2014)

ron45 said:


> If the spark plugs did good...the name etc., is usually written on the plug.


Thanks...but I already addressed this in post #8, "...If I can't find the OEM's recommendation, I'll pull the plugs and buy the same again...or equivalents (lol)."


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## SeniorSitizen (Sep 10, 2012)

Evidently there's money in plug manufacture and sales or there wouldn't be nearly the number of choices we have as equivalents.

There is 2 examples I've had in my lifetime where supposedly equivalents did not work well. In a 283 cubic inch chevy a ford number equivalent would make one believe he was on the verge of walking home. 

The second was the later in life when the ever so popular NGK plug evolved on the market. In a new 7,042 cubic inch Waukesha natural gas engine those plugs didn't make it 24 hours. I know that first hand because I was back to the location in the middle of the night replacing those NGK with the Champion plugs that had proven themselves for so many years.

If you wonder why your natural gas bill seems ridiculous a set of 12 RM77N plugs now runs in the neighborhood of $300.00. That's cheeeep compared to some plugs Caterpillar require.


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