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Quick "stupid" question about spark plugs

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updara

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Discussion starter · #1 ·
alight, i have a quick, yet may come off as stupid to some, question. But is their any danger of running spark plugs to long? I know after awhile, and lots of use, the gap can widen and become larger, yada yada yada, but is their any danger in running one to long if you just re-gap it? the ngk spark plug in my lawn mower had been in there for 5 years, and i've never taken it out to check the gap. My question is, will running it to long without taking it out and checking the gap hurt anything, if it's still running good? it's running fine, so i don't see a need to pull it out, but will any "odd" thing happen, like say when a spark plug gets old, it loses it's "power" and doesn't fire good enough and stuff like, say carbon, can build up because the plug is old? If you do take one out and re-gap it, and put it back in, will anything bad become of the equipment because the plug is old?

I know some people change their plugs every year or two years, but i can't see a reason for it, other than they just want a new one? If it's running good, why would they take it out and change it? to me it's just a waste of time, wear and tear on the spark plug threads, and waste of money, but is there a reason they do it?
 
#2 ·
I have no idea what engine you have but if it's a Kaw, check your manual that accompanied the engine--if I remember correctly they recommend replacing the plug every 100 hours--that's the best reason. New plugs, air filter, oil filter, oil, blade sharpening/replacement along with any adjustments, were all part of the Preventative Maintenance package our shop provided. I don't recall the recommendations other manufacturers may have.

Certainly you can run a plug as long as you'd like but at a buck 99 each, they're about the cheapest maintenance item you can invest in.
 
#4 ·
updara said:
it loses it's "power" and doesn't fire good enough and stuff like, say carbon, can build up because the plug is old?

That's all that will happen.....

If you do take one out and re-gap it, and put it back in, will anything bad become of the equipment because the plug is old?

No
Click to expand...
If your too lazy to clean or too cheap to replace the plug run it till it quits, Then you'll have to buy one and replace it.

Most change them because they do get to a point of not firing correctly or drop spark completely, They'd rather not be down in the middle of a job.....
 
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Discussion starter · #5 ·
Restrorob said:
If your too lazy to clean or too cheap to replace the plug run it till it quits, Then you'll have to buy one and replace it.

Most change them because they do get to a point of not firing correctly or drop spark completely, They'd rather not be down in the middle of a job.....
Click to expand...
when you say "you'll have to buy one to replace it" are you talking about new plug or new equipment

I always carry around extra plugs with me in the vehicle for back up, so i'm not that worried about getting knocked out in the middle of a job
 
#6 ·
restrorob said:
if your too lazy to clean or too cheap to replace the plug run it till it quits, then you'll have to buy one and replace it.
Click to expand...
......................... ;)
 
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#8 ·
I don't see anything terribly wrong by not replacing it. Now as the plug gets hours on it, you could notice more fuel consumption do to the plug not burning the fuel completely but then you would also notice a drop in power, starting etc. possibly the plug threads could seize in the motor which would be a problem to deal with. I think it's really more of a preventative maintenance thing like said above.
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Discussion starter · #9 ·
exmarkking said:
possibly the plug threads could seize in the motor which would be a problem to deal with.
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Click to expand...
I can agree with that, because i don't use, and will not use anti seize on spark plug threads. on NGk's website it says the coating used on the threads of their plug resist corrosion and will act as a release agent when you take it out. i seen else where that this only works once, so if you take it out, then put it back in, it loses it's "releasing" power. So i guess that would then be a good reason to replace it with just a new one. I pulled the champion outta my chainsaw just a bit ago, because i don't like champion plugs, and put a denso in, and it runs better, so i may/ may not just go ahead and replace them once a year, as others say is a good preventative measure. after all, ben franklin did say an ounce of prevention beats a pound of cure! I was just worried about stripping the threads outta the head. it would be ashamed to ruin a 400 dollar weedeater just by changing a 3 dollar spark plug! lol
 
Discussion starter · #10 ·
On the topic of spark plug threads, has any one here ever stripped the threads and fixed the problem without buying a new head? i got the idea once to use JB weld. lol


I may have to change the plugs in my RX-7 soon, and i'm paranoid of stripping the threads in it, because it would be a MAJOR PITA to find another rotor housing and having to strip down the engine! :realmad:
 
#12 ·
updara said:
On the topic of spark plug threads, has any one here ever stripped the threads and fixed the problem without buying a new head? i got the idea once to use JB
Click to expand...
Most stripped spark plug threads can be repaired using heli-coils, or other inserts made for restoring threads. Some ya can do in-place, others ya gotta pull the head. Not usually a big deal on a lawn mower.

I might add, I have to agree with your thread title!!!
 
#13 ·
updara said:
I can agree with that, because i don't use, and will not use anti seize on spark plug threads. on NGk's website it says the coating used on the threads of their plug resist corrosion and will act as a release agent when you take it out.
Click to expand...
Now that is something I didn't know. Back when I started, everything
was cast iron, so all plugs I installed got some kind of lube.
Now a days, I just use Fluid Film. The trick is not to over tighten the plug when you install it.
 
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#15 ·
updara said:
... is their any danger of running spark plugs to long? I know after awhile, and lots of use, the gap can widen and become larger, yada yada yada, but is their any danger in running one to long if you just re-gap it?
Click to expand...
Yes. Spark plug gap is directly related to arc voltage. Increase the gap, and you increase the voltage. Higher voltages mean you're aging your coil and ignition circuits more quickly. This is especially true on a "wasted spark" engine that erodes the plugs twice as fast, and sparks twice as often.

Regapping plugs does not put them back into new condition.
Another thing that is directly related to arc voltage is the sharpness of the electrode. As the gap erodes, the electrode rounds over and gets increasingly domed. When it starts out as a cylinder, the circular edge of that cylinder is sharp enough to keep the voltage relatively low. As the edge rounds over, the voltage increases, even if you maintain the gap to be the same.
 
#17 ·
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#19 ·
updara said:
alight, i have a quick, yet may come off as stupid to some, question. But is their any danger of running spark plugs to long? I know after awhile, and lots of use, the gap can widen and become larger, yada yada yada, but is their any danger in running one to long if you just re-gap it? the ngk spark plug in my lawn mower had been in there for 5 years, and i've never taken it out to check the gap. My question is, will running it to long without taking it out and checking the gap hurt anything, if it's still running good? it's running fine, so i don't see a need to pull it out, but will any "odd" thing happen, like say when a spark plug gets old, it loses it's "power" and doesn't fire good enough and stuff like, say carbon, can build up because the plug is old? If you do take one out and re-gap it, and put it back in, will anything bad become of the equipment because the plug is old?

I know some people change their plugs every year or two years, but i can't see a reason for it, other than they just want a new one? If it's running good, why would they take it out and change it? to me it's just a waste of time, wear and tear on the spark plug threads, and waste of money, but is there a reason they do it?
Click to expand...
So updara,

Just wondering if you feel the same way about changing the oil or the air filter in this mower? I mean if all this discussion and thought so far is over a $2.00 plug, I can only imagine what your thoughts might be on wasting money on an air filter and oil?
 
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#20 ·
BigFish said:
Please, elaborate.........I got time!
Click to expand...
Which part?

Spark plug gap is related to arc voltage? That's easy. An ignition circuit ramps up the voltage off the coil until the breakdown voltage of the fuel/air mixture in the arc gap is exceeded, after which a plasma channel forms between the two surfaces (the arc, aka spark), which forms a conductive path that limits the voltage. Double the distance that conductive path has to travel, and you double the voltage necessary to reach the breakdown voltage.

Quoting this page (because they actually put it quite well):
http://en.wikipedia.org/wiki/Spark_plug
"electrons are emitted where the electrical field strength is greatest; this is from wherever the radius of curvature of the surface is smallest, from a sharp point or edge"

What this means is that the breakdown voltage needed to begin electron transmission through the air (the start of the conductive plasma arc) is lower when the electrode is new and sharp, than when it is worn and rounded.
So a rounded electrode at the same gap will have a higher peak voltage.

These are not the kinds of household voltages you have running to your outlets. You're talking about many thousands of volts. Enough that if it doesn't spark across the plug, it can easily exceed the breakdown voltage of the spark plug wire, or the thin layer of varnish insulating the coil (maybe there was a bubble somewhere in the epoxy potting), or whatever the weakest link happens to be. As it happens, the plasma channel that passes through the insulation forms a carbon conductive path that is permanent (unlike the plasma in the air), which is a common cause of coil and wire failure (short).

The point is that in the high kilovolts, insulators (except maybe the ceramic insulator of the plug itself) don't insulate so well, and don't behave in ways you may expect. Even the ceramic plug insulator can fail. If it gets dirty (say it was contaminated by anti-seize grease, which is largely metallic and conductive) the arc can travel along the outside of the ceramic forming a carbon channel along its surface. That is why the insulator has ribs on it. To increase that path length and make that less likely.
 
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