Spark plug theory and practice

[fractal]

My lawn mower did not want to start today. Smelled plenty of gas so pulled the plug to take a looksee. It didn't look bad but it didn't look new so I put it back in and tried again. Still didn't start so I replaced the plug. The beast started on the first pull and gave me full power, something I hadn't felt from it in a while.

The plug in it was one that the local mower shop put in when I took the mower in for a service. I had them do a full service on it a couple of years ago when I was busy. I looked it up and it is definately not a proper replacement part. I have replaced the oil twice since then but did not replace the plug.

I have read every site I can find on spark plugs and think I have a basic understanding on how they are rated (the number on american spark, aka champion, plugs get bigger as the plug gets hotter, the number on foreign spark plugs get smaller as the plug get hotter) but what I can't find is ... ok, a J19LM is a "hotter" plug than a J17LM, but by how much? A NGK B2LM is a hotter plug than a BM6A but again, how much? How is the hotness measured.

Also, are the exotic metal plugs really any better than plain old plugs in regular every day use? I can see how they might make sense in heavy duty applications but I can not think of a single spark plug I have ever replaced in the past 30 years that has shown any signs of being "worn out". They have all been perfectly gapped and the tip was always the same shape as new ones. I can buy J19LM's, what briggs and stratton say to use in pretty much every piece of lawn equipment I own, for 1.59, or I can spend 3.78 for a NGK B2LM, or I can spend a bunch more for a gold platinum model. I am frugle but don't mind spending the extra money if I get something tangible for it.

Hope this is the right topic to post this. I did search and was unable to find anything on this subject.

 

[W.T.McGlynn]

Go with B & S plug.
No need to use aything else.

 

[Steve S]

I would use the recommended plug. The heat range is how the plug loses heat the faster the heat loss the cooler the rating, too hot is bad too cold is bad.

 

[Torino]

AH, spark plugs. In reality, NO ONE really knows how the lowly spark plug fires fuel. There are several theories, (1) Thermal--the heat generated during spark does its thing. (2) Fractionation--molecules of metal ripping from the electrodes fire the charge. (3) The famous "ping-pong" effect. One molecule of gasoline FINALLY gets fired, and the resultant bouncing around fires the rest. Weird, YES. Known,NO. We do know that once the fireball exceeds 1/10 in. in diameter, things happen quite fast. AH, theory. Ask you Doctorate friends what gravity and light is, THEN things REALLY get confusing. Best regards, John--Las Vegas. Use what works!!!

 

[Jon]

A good friend once told me that Champion spark plugs are good for only 2 things - Dragsters and lawn mowers. That being said, I love Autolite plugs, hate Bosch, Champion plugs are good, NGK is hit or miss (hit = great, miss = never did work), and Denso seems to be just fine. I want to try those new E3 plugs. I have a motorcycle that requires a special NON resistor plug in a very specific heat range ('81 Honda CB900) and it's very picky about plugs, maybe I'll try E3 there. My other motorcycle is a Yamaha Venture Royale, which is a tourer built around the VMax engine (V4) and ever since putting Iridiums in it 2-3 years ago, it's started and ran perfectly. Otherwise once or even twice a year it would need plugs.

 

[MAJA]

quote:

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Originally posted by fractal:
My lawn mower did not want to start today.....................Still didn't start so I replaced the plug. The beast started on the first pull and gave me full power, something I hadn't felt from it in a while............................I can not think of a single spark plug I have ever replaced in the past 30 years that has shown any signs of being "worn out"..........

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I think you just contradicted yourself, as your original post seems to indicate you HAD a "worn out" plug. I dont think there are any "signs" or visual clues to indicate if a lawn mower plug is bad. Ive had similar experiences where I have pulled my hair out trying to start a mower, only to have it start right up, first pull, after putting in a new plug.
I dont have an answer as to why this happens. Perhaps sitting between mowings too long, or, a reaction to the head material after getting real hot, then real cool, or, moisture getting into the combustion chamber when cooling, as the odds are real good one of the valves will be open as it sits. Then, its a very short path into the engine, to the sparkplug. Maybe someone here can answer that better.
But a new B & S plug cant be too expensive to replace every year, or twice a year, can it?

 

[kenw]

often the mere act of removing and replacing the SAME plug can clear up the real root cause issue:

bad electrical contact at the lead gets reseated and cleaned,

corroded ground point/path (threads) gets cleaned by turning,

gunk on tip gets knocked off,

flooded cylinder dries out, etc, etc etc.....

simply replacing the plug does not mean the plug was bad.

 

[MAJA]

quote:

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Originally posted by Jon:
............I want to try those new E3 plugs...........

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Did you read on of my earlier posts about these new E3 plugs. I think it got "flamed" pretty good.
But I, too, would like to try these new plugs. But it seems JC Whitney is the only source. And their selection is not extensive, or complete. Do you know of another source to get these plugs?

In case you missed my earlier link to an article, here it is:

http://www.autofieldguide.com/articles/020503.html

And if anyone wants to "flame" these plugs, or the article, please go to the earlier posting.

 

[1sttruck]

In the cars I just use the recommended heat range in 'double platinum' Autolites, as single platimum tips seem to exhibit more erosion and the cars aren't used outside of 'typical' operating conditions. The diesel don't need none :^) When I use to drive bikes plugs made a bigger difference. A wrong heat range would foul or sieze an engine. Platimum plugs would last longer as the tips didn't erode as quickly, but regular NGK plugs provided better performance so I just replaced them more often. I haven't changed the plug in the lawn mower ever, I bought used about 12 years ago. A few years back I filed the tip a bit and reset it, and dutifully look at it a couple times a year.